JP2024077201A - Catalyst deterioration diagnostic device for internal combustion engine - Google Patents

Abstract

To early discover deterioration of an oxidation catalyst by diagnosing deterioration of the oxidation catalyst from new viewpoints.SOLUTION: A catalyst deterioration diagnostic device for an internal combustion engine includes: an oxidation catalyst 51 provided in an exhaust passage 30; a diesel particulate filter 52 provided downstream of the oxidation catalyst 51 in the exhaust passage 30; and catalyst deterioration determination means 71 for determining deterioration of the oxidation catalyst 51. During regeneration of the diesel particulate filter 52, on the basis of information on post injection integrated quantity that is integrated quantity of post injection for regenerating the diesel particulate filter 52 and on combustion soot integrated quantity that is integrated quantity of soot burned in the diesel particulate filter 52, the catalyst deterioration determination means 71 determines that the oxidation catalyst has deteriorated when a ratio of the combustion soot integrated quantity to the post injection integrated quantity becomes lower than a predetermined threshold value.SELECTED DRAWING: Figure 1

Description

The present invention relates to a catalyst deterioration diagnosis device for an internal combustion engine equipped with an oxidation catalyst and a diesel particulate filter.

Internal combustion engines such as diesel engines are provided with an exhaust purification device that purifies the exhaust gas discharged from the internal combustion engine. The exhaust purification device is disposed in the exhaust passage of the internal combustion engine and is provided with an oxidation catalyst and a diesel particulate filter (hereinafter abbreviated as "DPF").

For example, diesel fuel, which is used in diesel engines, contains sulfur components, and diesel fuel with high sulfur content may be used. In such cases, it is known that the sulfur components are adsorbed and deposited on the active points on the surface of the oxidation catalyst, causing the purification rate of the oxidation catalyst to decrease or deteriorate.

Patent document 1 discloses a method for diagnosing the deterioration state of such oxidation catalysts.

JP 2016-109070 A

By the way, when soot accumulates in the DPF, a so-called post-injection is performed, and fuel is burned in an oxidation catalyst upstream of the DPF to raise the temperature of the exhaust gas flowing into the DPF, and the high-temperature exhaust gas burns the soot in the diesel particulate filter.

However, when the oxidation catalyst deteriorates, there are concerns that the temperature on the inlet side of the diesel particulate filter will not rise as expected even if post injection is performed during DPF regeneration. If the temperature on the inlet side of the diesel particulate filter does not reach the regeneration temperature, feedback control is performed to make it reach the set regeneration temperature, but an unnecessary increase in the amount of post injection can cause a deterioration in fuel economy.

The purpose of this invention was made in consideration of the above problems, and is to provide a catalyst deterioration diagnosis device for an internal combustion engine that can detect oxidation catalyst deterioration at an early stage by diagnosing the deterioration of the oxidation catalyst caused by the adsorption and accumulation of sulfur components from a new perspective.

The present invention has been made to solve at least part of the above problems, and can be realized in the following aspects or application examples.
The catalyst deterioration diagnosis device for an internal combustion engine according to this application example is a catalyst deterioration diagnosis device for an internal combustion engine comprising an oxidation catalyst that is provided in an exhaust passage in order to purify exhaust gas discharged from the internal combustion engine and oxidizes components in the exhaust gas, a diesel particulate filter that is provided downstream of the oxidation catalyst in the exhaust passage, and catalyst deterioration determination means that determines deterioration of the oxidation catalyst, and the catalyst deterioration determination means determines that the oxidation catalyst has deteriorated when a ratio of the post injection accumulated amount to the post injection accumulated amount becomes lower than a predetermined threshold value during regeneration of the diesel particulate filter, based on information on a post injection accumulated amount, which is an accumulated amount of post injections for regenerating the diesel particulate filter, and a combustion soot accumulated amount, which is an accumulated amount of soot burned in the diesel particulate filter.

This application example makes it possible to diagnose the deterioration of the oxidation catalyst caused by the adsorption and accumulation of sulfur components from a new perspective, enabling early detection of the deterioration of the oxidation catalyst.

According to this invention, by diagnosing the deterioration of the oxidation catalyst from a new perspective, it becomes possible to detect the deterioration of the oxidation catalyst early.

1 is a schematic diagram showing an internal combustion engine, its intake and exhaust systems, and a catalyst deterioration diagnosis device according to an embodiment; 4 is a flowchart illustrating a diagnosis process performed by the catalyst deterioration diagnosis device according to the embodiment. 5A and 5B are diagrams showing judgment thresholds of the catalyst deterioration diagnosis device according to the embodiment, in which FIG. 5A shows judgment thresholds during automatic regeneration, and FIG. 5B shows judgment thresholds during manual regeneration. 4 is a flowchart showing a processing status of a vehicle using a diagnosis by the catalyst deterioration diagnosis device according to the embodiment.

The following describes the embodiments of the present invention with reference to the drawings. The following embodiments are merely examples, and are not intended to exclude the application of various modifications or techniques not explicitly stated in the embodiments. The configurations of the following embodiments can be modified in various ways without departing from the spirit of the embodiments. Furthermore, they can be selected or combined as necessary.

[1. Configuration]
First, the configuration of an intake and exhaust system of an internal combustion engine according to this embodiment will be described with reference to the schematic configuration diagram of Fig. 1. In this embodiment, the internal combustion engine is mounted on a vehicle.
1, the internal combustion engine 1 is a diesel engine and is configured to include a plurality of (for example, four) cylinders 11. However, only one of the cylinders 11 is illustrated here. Each cylinder 11 is equipped with a fuel injection valve 12, which is supplied with pressurized fuel from a common rail 13 and injects fuel into the corresponding cylinder 11 when the valve opens.

A high-pressure pump 14 is connected upstream of the common rail 13. Fuel (here, diesel) in a fuel tank 15 is sucked in and pressurized by the high-pressure pump 14 through a fuel filter 16 and supplied to the common rail 13. The common rail 13 is also provided with a rail pressure sensor 27 that detects the pressure of the fuel discharged from the common rail.

An intake manifold 17 is attached to the intake side of the internal combustion engine 1, and an intake passage 20 is connected to the intake manifold 17. In the intake passage 20, from the upstream side, an air filter 21, an air flow sensor 22 that measures the amount of intake air, a compressor 61 of a turbocharger 60, an intercooler 23, an intake air temperature sensor 24, and a throttle valve 25 are provided, and the downstream end of an EGR (exhaust gas recirculation) passage 40 is joined and connected immediately downstream of the throttle valve 25. In addition, downstream of this joining connection and upstream of the intake manifold 17, an intake manifold pressure sensor 26 that detects the pressure of the intake air entering the intake manifold 17 is provided.

An exhaust manifold 18 is attached to the exhaust side of the internal combustion engine 1, and an exhaust passage 30 is connected to the exhaust manifold 18. The upstream end of an EGR passage 40 is branched off and connected to the exhaust passage 30, and downstream of that is provided a turbine 62 of a turbocharger 60 that is connected coaxially to a compressor 61, and downstream of that are provided an exhaust flap 31 that operates an exhaust brake, a catalytic converter 50, and a muffler (not shown), in this order.
An EGR cooler 41 is disposed in the middle of the EGR passage 40, and an EGR valve 42 is provided immediately upstream of the portion of the EGR passage 40 which joins with the intake passage 20 downstream.

The catalytic converter 50 is provided with an oxidation catalyst (hereinafter also referred to as DOC) 51, a diesel particulate filter (hereinafter also referred to as DPF) 52, and a post-catalyst (hereinafter also referred to as CUC) 53 in this order from the upstream side.
The DOC 51 is configured, for example, by supporting a catalyst layer made of a precious metal such as platinum (Pt) on a honeycomb-type ceramic carrier, and oxidizes carbon monoxide (CO), hydrocarbons (HC), and soluble organic components (hereinafter also referred to as SOF) in particulate matter (hereinafter also referred to as PM) contained in the exhaust gas.

The DPF 52 is made of, for example, a honeycomb-type ceramic carrier, and by alternately closing the upstream and downstream openings of its numerous exhaust gas passages, it captures PM in the exhaust gas while allowing the exhaust gas to flow through the porous walls that form the passages.
The CUC 53 oxidizes and removes the remaining components (HC, CO) that have not been completely treated by the DPF 52 .

In addition, an inlet temperature sensor 32 is provided immediately upstream of the DOC 51 to detect the temperature of the exhaust gas flowing into the DOC 51, and an outlet temperature sensor 33 is provided immediately downstream of the DOC 51 to detect the temperature of the exhaust gas flowing out of the DOC 51. Furthermore, a differential pressure sensor 34 is provided downstream of the outlet temperature sensor 33 to detect the differential pressure between the immediately upstream and immediately downstream of the DPF 52.

Note that the configuration of the exhaust system of the internal combustion engine 1 shown in FIG. 1 is one example, and the configuration of the exhaust system to which the present invention can be applied is not limited to this. For example, the exhaust system may be equipped with a NOx catalyst that purifies NOx in the exhaust gas.

The vehicle is equipped with an ECU (electronic control unit) 7 that controls each part of the internal combustion engine 1. The ECU 7 includes an input/output device (not shown), a storage device (ROM, RAM, etc.) that stores control programs and control maps, a central processing unit (CPU), a timer counter, etc.

The input side of the ECU 7 is connected to the air flow sensor 22, intake air temperature sensor 24, intake manifold pressure sensor 26, rail pressure sensor 27, DOC inlet temperature sensor 32, DOC outlet temperature sensor 33, DPF differential pressure sensor 34, and other sensors (not shown) (e.g., accelerator opening sensor, engine speed sensor, water temperature sensor, outside air temperature sensor, outside air pressure sensor, etc.) and switches (e.g., starter switch, oil level switch, etc.), and detection signals from the sensors and on/off signals from the switches are input.

In addition, the output side of the ECU 7 is connected to the fuel injection valve 12, the fixed-volume high-pressure pump 14, the throttle valve 25, the EGR valve 41, the exhaust flap 31, as well as glow plugs and warning lights (not shown), and the operation of each is controlled based on the input information.
In other words, the ECU 7 sets target values for the fuel injection amount, injection timing, common rail pressure, etc. based on detection information such as the driver's accelerator operation amount (accelerator opening) and engine rotation speed, and operates the internal combustion engine 1 by controlling the drive of the fuel injection valve 12 and adjusting the common rail pressure based on these values.

During operation of the internal combustion engine 1, exhaust gas from the internal combustion engine 1 flows from the exhaust manifold 18 into the exhaust passage 30, passes through the DOC 51, where HC, CO and unburned fuel in the exhaust gas are combusted, and the exhaust gas flows into the DPF 52. In the DPF 52, PM contained in the exhaust gas is trapped as it flows through the walls of the passage, and then excess HC and CO are oxidized and removed in the CUC 53, and the PM is discharged into the atmosphere.
As the PM is trapped, the amount of trapped PM on the DPF 52 gradually increases, but when the internal combustion engine 1 is in a predetermined operating state (for example, an operating state in which the exhaust gas temperature is relatively high), the trapped PM is continuously incinerated and removed by using, as an oxidizing agent, _NO2 generated from NO in the exhaust gas by an oxidation reaction on the upstream DOC 51.

Furthermore, if an operating state in which such continuous regeneration of the DPF 52 cannot be achieved continues, the amount of PM trapped in the DPF 52 will gradually increase and exceed the allowable amount. To avoid this situation, data on parameters related to the amount of trapped PM is constantly monitored, the amount of trapped PM is estimated based on this monitored data, and when the estimated amount of trapped PM reaches the allowable amount (threshold value), forced regeneration (hereinafter also simply referred to as "regeneration") is performed to forcibly incinerate and remove the PM on the DPF 52.

This PM collection amount can be estimated, for example, by having the ECU 7 successively calculate and accumulate the amount of PM collected in the DPF 52 based on the operating state of the internal combustion engine 1. When this PM accumulation value reaches or exceeds a PM amount threshold set based on the allowable amount of the DPF 52, it is estimated that the PM collection amount is approaching the allowable amount, and forced regeneration is performed.

In addition, in this embodiment, in parallel with this, the differential pressure sensor 34 detects the differential pressure before and after the DPF 52 (pressure loss in the DPF 52), which rises as the amount of PM trapped increases, and when the differential pressure before and after this differential pressure reaches or exceeds a predetermined differential pressure threshold, forced regeneration is performed to forcibly incinerate and remove the PM on the DPF 52.

In addition to the above, in this embodiment, when the cumulative operating time of the internal combustion engine 1 after the previous regeneration reaches or exceeds a predetermined time, a forced regeneration is performed to forcibly incinerate and remove the PM on the DPF 52. In other words, forced regeneration is performed when any of the following is true: the PM integrated value reaches or exceeds the PM amount threshold, the differential pressure before and after the DPF 52 reaches or exceeds the differential pressure threshold, or the cumulative operating time of the internal combustion engine 1 after the forced regeneration reaches or exceeds a predetermined time.

In this embodiment, post (so-called late post) injection is used for forced regeneration. Post injection is performed after main injection to supply unburned fuel to the DOC 51, and the heat generated when the unburned fuel undergoes an oxidation reaction on the DOC 51 raises the temperature of the downstream DPF 52 to a target temperature (a temperature at which PM can be burned and removed), thereby burning and removing the PM. Note that forced regeneration is performed by estimating the gas temperature of the DPF 52 from the outlet temperature Tout detected by the outlet temperature sensor 33, and bringing this gas temperature close to the target temperature.

This forced regeneration of the DPF 52 is performed automatically while the vehicle is running (automatic regeneration), but it can also be performed manually while the vehicle is stopped (manual regeneration) by operating a manual regeneration switch (not shown) equipped on the vehicle when the vehicle is stopped.

The temperature rise of the DPF 52 during forced regeneration depends on the oxidation function of the DOC 51, and deterioration of the DOC 51 leads directly to the inability to execute forced regeneration, and ultimately to a decline in exhaust gas purification performance and driving performance. Therefore, in the vehicle of this embodiment, a catalyst deterioration determination unit (catalyst deterioration determination means) 71 provided in the ECU 7 performs deterioration diagnosis of the DOC 51 during forced regeneration (during automatic regeneration and manual regeneration). Details of the deterioration diagnosis of the DOC 51 by the catalyst deterioration determination unit 71 are described below.

In this embodiment, the catalyst deterioration determination unit 71 performs deterioration diagnosis of the DOC 51 by two diagnosis methods.
The first diagnostic method (method 1) is a well-known deterioration diagnosis based on the temperature rise state of the DPF 52 due to post injection. That is, if the outlet temperature Tout of the DOC 51 (= the inlet temperature of the DPF 52) detected by the outlet temperature sensor 33 does not rise to or exceed a predetermined temperature threshold even after post injection is performed for a predetermined time (or a predetermined period), the catalyst deterioration determination unit 71 diagnoses that the DOC 51 is degraded as the DOC 51 is not functioning sufficiently.

The second diagnostic method (Method 2) is a diagnostic method specific to this case, and is a deterioration diagnosis based on the ratio of the accumulated amount of combustion soot to the accumulated amount of post-injection. This deterioration diagnosis will be explained in detail with reference to Figure 2.

As shown in FIG. 2, when forced regeneration of the DPF 52 begins, the catalyst deterioration determination unit 71 performs the following processes. First, it calculates the post injection cumulative amount Ap, which is the cumulative amount of post injections to regenerate the DPF 52 (step SS10). During regeneration of the DPF 52, the post injection amount for each cycle is set according to the operating state of the internal combustion engine 1, and by accumulating this, it is possible to calculate the post injection cumulative amount Ap.

In parallel with the post-injection cumulative amount Ap, the cumulative amount of burned soot As, which is the cumulative amount of soot burned in the DPF 52, is calculated (step SS20). Since the amount of burned soot depends on the filter temperature, gas flow rate, oxygen flow rate, excess air ratio (λ), etc., the amount of burned soot in each cycle can be calculated based on these data, and the cumulative amount of burned soot As can be calculated by accumulating these.

Next, the ratio R (=As/Ap) of the accumulated amount of combustion soot As to the accumulated amount of post injection Ap is calculated (step SS30). The calculated ratio R is then compared with a predetermined threshold value Rs set in advance to determine whether the ratio R is lower than the threshold value Rs (step SS40). As a result, when the ratio R is lower than the threshold value Rs, it is determined that the DOC 51 has deteriorated (step SS50). On the other hand, when the ratio R is not lower than the threshold value Rs, it is determined that the DOC 51 is normal (step SS60).
This process is repeated at a predetermined interval during forced regeneration.

However, in this embodiment, the threshold value Rs is set to a different value during automatic regeneration and during manual regeneration, which will be described with reference to FIG.
In Fig. 3, the horizontal axis represents the post injection integrated amount Ap and the regeneration time (post injection time), and the vertical axis represents the combustion soot integrated amount As, and the slope S of the straight line in the figure represents the ratio R. Fig. 3(a) explains the threshold value Rs1 during automatic regeneration, and Fig. 3(b) explains the threshold value Rs2 during manual regeneration.

As shown in Figures 3(a) and (b), when the soot in the DPF 52 is completely combusted by forced regeneration, the slope S is at its maximum, but in actual forced regeneration, the theoretical perfect combustion is not reached and the slope is generally smaller than that of complete combustion. This slope depends on the conditions during regeneration; if the conditions are good, the slope approaches the slope of complete combustion, but the worse the conditions are, the smaller the slope becomes and the further it moves away from the slope of complete combustion. The conditions that cause this include the operating state of the internal combustion engine 1; if the operating state of the internal combustion engine 1 is stable, the slope S tends to be large, and if the operating state of the internal combustion engine 1 changes, the slope S tends to be small. The conditions also include the performance of the DOC 51, and the slope S becomes small as the DOC 51 deteriorates.

Automatic regeneration is performed under various operating conditions of the internal combustion engine 1 while the engine is running, and therefore may be in poor conditions, whereas manual regeneration is performed while the engine is stopped and therefore is performed in relatively stable and good conditions. For this reason, as shown in Fig. 3(b), the slope S (= S1) during automatic regeneration tends to be smaller than the slope S (= S2) during manual regeneration, and even if the DOC 51 deteriorates, the slope S during automatic regeneration is smaller than the slope S during manual regeneration.
3A and 3B, the threshold value Rs1 during automatic regeneration is set to a value different from the threshold value Rs2 during manual regeneration, thereby reducing the risk of false detection during automatic regeneration.

In the deterioration diagnosis device, the deterioration determination of the DOC 51 by the catalyst deterioration determination unit 71 is utilized to perform a diagnosis process for the vehicle as shown in FIG.
That is, when the DPF automatic regeneration is started, the deterioration diagnosis of the DOC 51 is performed using the above-mentioned first method (method 1) and second method (method 2) (step S10). In this case, in method 2, the threshold value Rs1 during automatic regeneration is used. If deterioration is not judged in either method 1 or method 2, the DOC 51 is judged to be normal (not deteriorated), and if it is before the end of automatic regeneration, automatic regeneration is continued, and if it is the automatic regeneration end timing, automatic regeneration is completed (step S20). On the other hand, if deterioration is judged in either method 1 or method 2, the DOC 51 is judged to be deteriorated, and automatic regeneration is prohibited (step S30).

In this embodiment, when automatic regeneration is prohibited, there is a possibility of performing manual regeneration. When the conditions for manual regeneration are met and manual DPF regeneration is started, the deterioration diagnosis of the DOC 51 is performed using the above-mentioned first method (method 1) and second method (method 2) in the same manner as described above (step S40). In this case, method 2 uses the threshold value Rs2 during manual regeneration. If neither method 1 nor method 2 determines that the DOC 51 is deteriorated, the DOC 51 is determined to be normal (not deteriorated), and if it is before the end of manual regeneration, manual regeneration is continued, and if it is the timing to end manual regeneration, manual regeneration is completed (step S50). After that, the error during automatic regeneration is cleared (step S60), and automatic regeneration is permitted (step S70). On the other hand, if deterioration is determined by either method 1 or method 2, the DOC 51 is determined to be deteriorated, manual regeneration is prohibited, and a warning lamp is turned on (step S80). Then, if the deterioration is reached, in this embodiment, the DOC 51 is guided to a maintenance shop and repairs are performed (step S90). Then, the above steps S60 and S70 are performed.

[2. Actions and Effects]
The catalyst deterioration diagnosis device for an internal combustion engine in this embodiment is configured as described above, and as such, in addition to the well-known diagnosis method (Method 1), a deterioration diagnosis method (Method 2) based on the ratio of the accumulated amount of combustion soot to the accumulated amount of post injection, which is different from Method 1, is used to perform deterioration diagnosis of the DOC 51. This makes it possible to more quickly detect deterioration of the DOC 51, quickly perform deterioration response processing for the DOC 51, and suppress the implementation of inefficient post injection, thereby suppressing deterioration of fuel efficiency.

In addition, in this embodiment, the threshold value Rs1 for automatic regeneration is used during automatic regeneration, and the threshold value Rs2 for manual regeneration is used during manual regeneration to perform deterioration diagnosis of the DOC51, allowing for accurate diagnosis.

[3. Other]
Although the embodiment has been described above, this embodiment is merely an example, and the catalyst deterioration diagnosis device for an internal combustion engine of the present invention is not limited to the embodiment.
For example, in the above embodiment, the methods 1 and 2 are used in combination, but only the method 2 according to the present invention may be implemented.

1 Internal combustion engine 7 ECU (electronic control unit)
REFERENCE SIGNS LIST 11 cylinder 12 fuel injection valve 13 common rail 14 high-pressure pump 15 fuel tank 16 fuel filter 17 intake manifold 18 exhaust manifold 20 intake passage 21 air filter 22 air flow sensor 23 intercooler 24 intake air temperature sensor 25 throttle valve 26 intake manifold pressure sensor 27 rail pressure sensor 30 exhaust passage 31 exhaust flap 32 DOC inlet temperature sensor 33 DOC outlet temperature sensor 34 DPF differential pressure sensor 40 EGR (exhaust gas recirculation) passage 41 EGR cooler 42 EGR valve 50 catalytic converter 51 oxidation catalyst (DOC)
52 Diesel Particulate Filter (DPF)
53 Rear catalyst (CUC)
60 Turbocharger 61 Compressor of turbocharger 60 62 Turbine of turbocharger 60 71 Catalyst deterioration determination unit (catalyst deterioration determination means)

Claims (1)

A catalyst deterioration diagnosis device for an internal combustion engine, comprising: an oxidation catalyst that is provided in an exhaust passage to purify exhaust gas discharged from an internal combustion engine and oxidizes components in the exhaust gas; a diesel particulate filter that is provided downstream of the oxidation catalyst in the exhaust passage; and catalyst deterioration determination means that determines deterioration of the oxidation catalyst,
The catalyst deterioration determination means is a catalyst deterioration diagnosis device for an internal combustion engine that determines that the oxidation catalyst is deteriorated when a ratio of a post injection integrated amount, which is an integrated amount of post injections for regenerating the diesel particulate filter, to a combustion soot integrated amount, which is an integrated amount of soot burned in the diesel particulate filter, becomes lower than a predetermined threshold value during regeneration of the diesel particulate filter.

Images