JP7697392B2 - Exhaust purification equipment - Google Patents

Description

The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device that purifies exhaust gas emitted from an internal combustion engine.

In an internal combustion engine, feedback control of the air-fuel ratio is performed based on the output of an exhaust sensor that detects the state of the exhaust gas discharged from the internal combustion engine. If an abnormality occurs in this exhaust sensor, there is a risk that the accuracy of the air-fuel ratio feedback control will decrease, so it is necessary to diagnose the exhaust sensor for abnormalities.

Patent Document 1 discloses an air-fuel ratio detection sensor abnormality diagnosis device that includes a reaction delay determination unit that determines that an abnormality due to a reaction delay has occurred in the air-fuel ratio sensor when a reaction delay condition is satisfied a predetermined number of times, and a sensor abnormality diagnosis unit that diagnoses an abnormality in the air-fuel ratio sensor based on the determination result of the reaction delay determination unit. It is described that the technology described in Patent Document 1 makes it possible to accurately determine that an abnormality has occurred in the air-fuel ratio detection sensor that detects the air-fuel ratio of exhaust gas.

JP 2011-157938 A

The exhaust passage of an internal combustion engine may be equipped with a three-way catalyst that purifies the exhaust gas discharged from the internal combustion engine and a particulate filter that collects particulate matter in the exhaust gas. As particulate matter accumulates inside the particulate filter with use, the resistance to passage increases. Therefore, filter regeneration control is performed to remove the particulate matter collected in the particulate filter by varying the air-fuel ratio.

In this type of filter regeneration control, oxygen is supplied to the particulate filter, which allows the particulate matter trapped in the particulate filter to be burned and removed. Therefore, during filter regeneration control, the air-fuel ratio of the exhaust gas flowing into the particulate filter becomes an oxidizing atmosphere (lean).

On the other hand, when the exhaust is controlled to the lean side due to filter regeneration control, there is a risk of misdiagnosing the exhaust sensor abnormality if an abnormality diagnosis is performed on the exhaust sensor that detects the state value of the exhaust flowing into the particulate filter. In order to prevent such a misdiagnosis of the exhaust sensor abnormality, it is conceivable to not perform the exhaust sensor abnormality diagnosis during filter regeneration control, but in this case, there is a problem that the frequency of detecting an abnormality in the exhaust sensor decreases.

The present invention has been made to solve these problems, and aims to provide an exhaust purification device that increases the frequency with which abnormalities in the exhaust sensor are detected.

The exhaust purification device according to one embodiment includes a three-way catalyst provided in an exhaust passage of an internal combustion engine to purify exhaust gas discharged from the internal combustion engine, a particulate filter provided in an exhaust passage downstream of the three-way catalyst to capture particulate matter in the exhaust gas, an exhaust sensor to detect a state value related to the air-fuel ratio of the exhaust gas that has passed between the three-way catalyst and the particulate filter, and a control unit that, when the amount of accumulated particulate matter captured in the particulate filter is equal to or greater than a predetermined amount, executes filter regeneration control to burn the particulate matter captured in the particulate filter and regenerate the particulate filter by controlling the air-fuel ratio in the exhaust passage and upstream of the three-way catalyst to a value greater than the stoichiometric air-fuel ratio. When a prerequisite condition for diagnosing an abnormality of the exhaust sensor is satisfied, the control unit prohibits the filter regeneration control, and during the period when the filter regeneration control is prohibited, judges an abnormality of the exhaust sensor based on the response time of the exhaust sensor from the start of fuel cut control to stop fuel injection of the internal combustion engine until the state value reaches a predetermined value on the lean side from a specified air-fuel ratio equal to or less than the stoichiometric air-fuel ratio.

The present invention provides an exhaust purification device that increases the frequency with which abnormalities in the exhaust sensor are detected.

1 is a block diagram showing a configuration of an exhaust gas purification device according to a first embodiment; 4 is a flowchart showing a flow of a process for an exhaust sensor OBD executed by an ECU.

First embodiment
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In order to clarify the description, the following description and drawings are appropriately simplified. What is shown in the drawings is only a part of the whole, and in reality, many other configurations that are not shown are included. Furthermore, in the following description, the same or equivalent elements are given the same reference numerals, and duplicated descriptions are omitted.

First, the configuration of an exhaust gas purification device 1 according to this embodiment will be described with reference to FIG.
Fig. 1 is a block diagram for explaining the configuration of an exhaust gas purification device according to a first embodiment. Fig. 1 shows a main portion of a vehicle 100 related to the exhaust gas purification device 1. In this embodiment, an example will be explained in which the exhaust gas purification device 1 is applied to a vehicle 100 equipped with a gasoline engine.

The internal combustion engine 10 mounted on the vehicle 100 has a cylinder 11, a piston 12, an intake valve 13, an exhaust valve 14, a fuel injection valve 15, and an ignition plug 16. The internal combustion engine 10 is also connected to an intake passage 20 and an exhaust passage 30.

The piston 12 moves up and down inside the cylinder 11. The intake valve 13 is provided at an intake port of the intake passage 20 facing the cylinder 11. The exhaust valve 14 is provided at an exhaust port of the exhaust passage 30 facing the cylinder 11. The fuel injection valve 15 and the spark plug 16 are provided so that their tips face inside the cylinder 11. The fuel injection valve 15 and the spark plug 16 are driven and controlled by a control unit (ECU 50). Furthermore, the internal combustion engine 10 is provided with a water temperature sensor 17 that detects the temperature of the cooling water passing through a cooling water passage formed in the housing of the internal combustion engine 10. The water temperature sensor 17 outputs the detected temperature of the cooling water to the ECU 50 as the engine cooling water temperature.

The intake passage 20 is provided with an air filter 21, an air flow meter 22, and a throttle valve 23. The air filter 21 is disposed at the upstream end of the intake passage 20. An intake air temperature sensor (not shown) that detects the intake air temperature (i.e., outside air temperature) is attached to the air filter 21. An air flow meter 22 is disposed downstream of the air filter 21. The air flow meter 22 is a sensor that detects the amount of intake air flowing through the intake passage 20. The air flow meter 22 outputs the detected amount of intake air to the ECU 50. A throttle valve 23 is disposed downstream of the air flow meter 22. A throttle sensor 24 that detects the throttle opening is disposed near the throttle valve 23. The throttle valve 23 is driven by the ECU 50 to adjust the amount of intake air supplied to the cylinder 11.

In the internal combustion engine 10, when the piston 12 descends, the intake valve 13 opens and air is drawn into the cylinder 11 from the intake passage 20, and fuel is injected from the fuel injection valve 15 to form an air-fuel mixture in the cylinder 11 (intake stroke). When the piston 12 rises again, the intake valve 13 closes and the formed air-fuel mixture is compressed (compression stroke). The compressed air-fuel mixture is ignited by the spark plug 16 and expands, pushing the piston 12 down (expansion stroke). When the piston 12 rises again, the exhaust valve 14 opens and the combustion gas (exhaust) is discharged into the exhaust passage 30 (exhaust stroke).

The exhaust passage 30 is provided with a three-way catalyst 31 and a particulate filter (GPF) 32. The three-way catalyst 31 is a catalyst having oxygen storage and release performance, and purifies the exhaust gas by oxidizing or reducing hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides ( _NOx ) in the exhaust gas discharged from the internal combustion engine 10. For example, the three-way catalyst 31 adsorbs oxygen in the exhaust gas when the exhaust gas is rich, and releases the adsorbed oxygen when the exhaust gas is lean, thereby purifying the HC, CO, _NOx, and the like in the exhaust gas.

A particulate filter 32 is disposed downstream of the three-way catalyst 31. The particulate filter 32 collects particulate matter (PM) contained in the exhaust gas. The PM collected in the particulate filter 32 is burned (oxidized) by oxygen being supplied to the particulate filter 32 when the particulate filter 32 is in a high temperature state.

Also, the particulate filter 32 may be, for example, a filter having an oxygen storage and release function configured by carrying a catalytic component on the surface of a filter carrier. The particulate filter 32 carrying the catalytic component also functions as a three-way catalyst 31, and purifies the exhaust gas by oxidizing or reducing HC, CO, and _NOx in the exhaust gas. By providing the particulate filter 32 with the function of a three-way catalyst in addition to the three-way catalyst 31, the efficiency of purifying the exhaust gas is improved.

In addition, an exhaust sensor 33 is provided in the exhaust passage 30. The exhaust sensor 33 is disposed between the three-way catalyst 31 and the particulate filter 32, downstream of the three-way catalyst 31 and upstream of the particulate filter 32.

The exhaust sensor 33 is a sensor that detects a state value related to the air-fuel ratio of the exhaust gas that has passed between the three-way catalyst 31 and the particulate filter 32. The exhaust sensor 33 outputs the detected state value to the ECU 50. An air-fuel ratio sensor or an oxygen concentration sensor can be used as the exhaust sensor 33. The air-fuel ratio sensor is a sensor that outputs a linear signal corresponding to the air-fuel ratio of the exhaust gas, and detects the air-fuel ratio (A/F) as the state value. The oxygen concentration sensor is a sensor that outputs a signal corresponding to the oxygen concentration in the gas, and detects the oxygen concentration as the state value.

An exhaust temperature sensor that measures the temperature of the exhaust gas may be provided in the exhaust passage 30 downstream of the three-way catalyst 31 and upstream of the particulate filter 32. The temperature of the three-way catalyst 31 or the particulate filter 32 can be estimated based on the output of the exhaust temperature sensor. Note that even if no exhaust temperature sensor is provided, the temperatures of the three-way catalyst 31 and the particulate filter 32 can also be estimated based on the operating state of the internal combustion engine 10.

The exhaust purification device 1 has an ECU (Electronic Control Unit) 50 as a control unit. The ECU 50 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a storage device. The CPU loads various control programs stored in the ROM and data referenced when executing the various control programs into the RAM to perform calculations.

In addition to the above-mentioned sensors, various sensors that detect the operating state of the internal combustion engine 10, including an accelerator opening sensor and a crank position sensor, are connected to the ECU 50. The ECU 50 receives a signal corresponding to the accelerator opening from the accelerator opening sensor, and calculates the accelerator operation amount and the engine load required of the internal combustion engine 10 based on this signal. The ECU 50 also receives a signal corresponding to the rotation angle of the output shaft of the internal combustion engine 10 from the crank position sensor, and calculates the engine speed of the internal combustion engine 10. The ECU 50 is also connected to various actuators such as the throttle valve 23, fuel injection valve 15, and spark plug 16.

Based on signals input from various sensors, the ECU 50 performs various controls of the internal combustion engine 10, including control of the fuel injection amount of the fuel injection valve 15, control of the ignition timing of the spark plug 16, and control of the throttle opening (amount of intake air) of the throttle valve 23.

During normal operation of the vehicle 100, when a predetermined condition for executing air-fuel ratio feedback control is met, the ECU 50 executes air-fuel ratio feedback control, which feedback controls the air-fuel ratio of the mixture (fuel injection amount and intake air amount) based on the state value of the exhaust sensor 33 so that the air-fuel ratio of the exhaust matches the theoretical air-fuel ratio (stoichiometric), which is the target air-fuel ratio.

In addition, in the fuel injection amount control, when the vehicle 100 is decelerating or coasting, the ECU 50 executes fuel cut control to stop fuel injection of the internal combustion engine 10. During fuel cut control, the ECU 50 supplies air into the cylinder 11 with fuel injection by the fuel injection valve 15 stopped. For example, when the engine speed is equal to or higher than a predetermined speed while the vehicle 100 is running, if the accelerator operation amount becomes zero, fuel cut control is started. The fuel cut control reduces fuel consumption and increases the oxygen concentration in the exhaust gas, allowing the PM captured in the particulate filter 32 to be burned.

The ECU 50 also estimates the amount of PM trapped in the particulate filter 32 (hereinafter, PM accumulation amount). When the ECU 50 estimates the amount of PM accumulation, it may estimate it based on the past engine speed and engine load, or it may estimate it based on the difference between the exhaust pressure upstream of the particulate filter 32 and downstream of the three-way catalyst 31 and the exhaust pressure downstream of the particulate filter 32 (hereinafter, filter pressure difference), and the exhaust flow rate.

Here, since the engine speed and engine load are related to the amount of PM discharged from the internal combustion engine 10, the amount of PM discharged from the internal combustion engine 10 can be calculated based on the engine speed and engine load. The amount of PM deposition can be calculated by integrating the amount of PM discharged from the internal combustion engine 10. On the other hand, the greater the amount of PM deposition, the greater the filter differential pressure. This filter differential pressure also varies depending on the exhaust flow rate. Therefore, if the relationship between the amount of PM deposition, the filter differential pressure, and the exhaust flow rate is determined in advance by experiment or simulation, the amount of PM deposition can be calculated from the filter differential pressure and the exhaust flow rate. Furthermore, since the amount of PM deposition increases depending on the operating time of the internal combustion engine 10 or the distance traveled by the vehicle 100, the amount of PM deposition can also be easily estimated based on these values.

Then, when the amount of PM accumulation is equal to or greater than a predetermined amount, the ECU 50 executes filter regeneration control to burn PM in order to regenerate the particulate filter 32. Specifically, the ECU 50 appropriately adjusts the fuel injection amount, injection timing or number of injections by the fuel injection valve 15, and the ignition timing or number of ignitions by the spark plug 16, etc., to control (lean control) the air-fuel ratio in the exhaust passage 30 and upstream of the three-way catalyst 31 to a value greater than the theoretical air-fuel ratio. By controlling in this manner, oxygen can be supplied to the particulate filter 32, and the PM trapped in the particulate filter 32 can be burned to regenerate the particulate filter 32. The predetermined amount is the amount of PM accumulation at which it is desirable to perform regeneration of the particulate filter 32. If the predetermined amount is too small, regeneration of the particulate filter 32 will be performed frequently, which may lead to a deterioration in fuel efficiency. On the other hand, if the predetermined amount is too large, there is a concern that the output of the internal combustion engine 10 will decrease due to an increase in exhaust pressure. Taking these factors into consideration, the specified amount is determined in advance through experiments or simulations, etc.

Furthermore, when the exhaust sensor 33 abnormality diagnosis precondition (exhaust sensor OBD precondition) described below is satisfied, the ECU 50 prohibits filter regeneration control, and during the period when filter regeneration control is prohibited, judges whether the exhaust sensor 33 is abnormal (deteriorated responsiveness) based on the response time of the exhaust sensor 33 from the start of fuel cut control until the state value reaches a predetermined value on the lean side from a specified air-fuel ratio below the theoretical air-fuel ratio (stoichiometric).

Then, referring to FIG. 2, the process flow of the exhaust sensor 33 abnormality diagnosis (exhaust sensor OBD) executed by the ECU 50 will be described. FIG. 2 is a flowchart showing the flow of the exhaust sensor OBD process executed by the ECU. The following description will be given taking as an example a case where the exhaust sensor 33 is an air-fuel ratio sensor. Also, in this embodiment, the case where the specified air-fuel ratio is stoichiometric will be described, but the specified air-fuel ratio is not limited to stoichiometric and may be an air-fuel ratio on the rich side.

The process flow shown in FIG. 2 is realized by repeatedly executing a program prestored in the ECU 50 at a predetermined interval while the ECU 50 is powered on (while the ignition switch is on). Alternatively, the process can be realized by constructing some or all of the steps of the program using dedicated hardware.

2 is started during execution of filter regeneration control, the ECU 50 determines whether the exhaust sensor OBD preconditions for executing the exhaust sensor OBD are met (step S1). Specifically, when all of the following conditions (1) to (3) are met, the ECU 50 determines that the exhaust sensor OBD preconditions are met (step S1: YES) and proceeds to step S2.

Condition (1): The engine coolant temperature detected by the water temperature sensor 17 is equal to or higher than a predetermined value (for example, 75° C.).
Condition (2): The state value detected by the exhaust sensor 33 is stoichiometric (for example, 16).
Condition (3): The three-way catalyst 31 is in an active state.

Whether the three-way catalyst 31 is active or not can be determined based on the temperature of the three-way catalyst 31.

On the other hand, if at least one of the exhaust sensor OBD preconditions is not met, the ECU 50 determines that the exhaust sensor OBD precondition is not met (step S1: NO) and returns the process to step S1 (RETURN).

If the exhaust sensor OBD precondition is met in step S1, the ECU 50 prohibits filter regeneration control (step S2). The ECU 50 sets a regeneration control prohibition request flag to ON. The regeneration control prohibition request flag is a flag that is set to ON when filter regeneration control is prohibited and is set to OFF when filter regeneration control is not prohibited. When the regeneration control prohibition request flag is set to ON, the air-fuel ratio control associated with the filter regeneration control is stopped.

Then, the ECU 50 determines whether or not fuel cut control is being executed (step S3). This determination is made based on the state of the fuel cut flag. The fuel cut flag is a flag that is set ON when fuel cut control is being executed and is set OFF when fuel cut control is not being executed. Here, the ECU 50 executes fuel cut control when the accelerator operation amount becomes zero while the vehicle 100 is running and the engine speed is equal to or higher than a predetermined speed. On the other hand, if the accelerator operation amount increases while fuel cut control is being executed, the ECU 50 stops the fuel cut control and resumes fuel injection.

If fuel cut control is being executed (step S3: YES), proceed to step S4. If fuel cut control is not being executed (step S3: NO), return to step S1.

If fuel cut control is being executed, the ECU 50 determines whether the state value of the exhaust sensor 33 before the fuel cut control is started is stoichiometric (prescribed air-fuel ratio) (step S4). If the state value of the exhaust sensor 33 before the fuel cut control is started is stoichiometric (step S4: YES), the process proceeds to step S5. If the state value of the exhaust sensor 33 before the fuel cut control is started is not stoichiometric (step S4: NO), the process skips steps S5 and S6 and ends the process flow shown in FIG. 2.

If the state value of the exhaust sensor 33 before the fuel cut control starts is stoichiometric, the ECU 50 measures the response time of the exhaust sensor 33 (step S5). Specifically, when the fuel cut control starts, the state value of the exhaust sensor 33 changes to the lean side due to the stop of fuel injection. Therefore, the ECU 50 measures the time required for the state value of the exhaust sensor 33 to change from stoichiometric to a lean state value (e.g., 18), which is a predetermined value leaner than stoichiometric, as the response time of the exhaust sensor 33. Note that the stoichiometric and lean state values are set appropriately depending on the internal combustion engine 10 and the properties of the fuel.

Then, the ECU 50 performs a process to determine whether the exhaust sensor 33 is normal or abnormal (step S6). Specifically, if the response time measured in step S5 is equal to or less than a preset reference response time, it determines that the exhaust sensor 33 is normal (normal determination) and keeps the abnormality flag OFF. On the other hand, if the measured response time exceeds the preset reference response time, it determines that an abnormality has occurred in the exhaust sensor 33 (abnormal determination) and sets the abnormality flag ON.

The standard response time is set appropriately depending on the exhaust sensor 33 that is the target of the abnormality diagnosis. When an abnormality occurs in the exhaust sensor 33, a failure flag may be stored internally as necessary, or an abnormality lamp may be turned on to notify the driver.

The ECU 50 stores the results of the abnormality diagnosis in the memory of the ECU 50 as necessary. In this manner, a series of processing flows for the exhaust sensor OBD is carried out. If there is a history of a normal/abnormal determination, the next processing cycle is not executed.

In this manner, in a configuration in which a three-way catalyst 31 and a particulate filter 32 are provided in the exhaust passage 30, and an exhaust sensor 33 is provided between the three-way catalyst 31 and the particulate filter 32, filter regeneration control is performed when the amount of PM accumulation increases.

During filter regeneration control, the temperature of the particulate filter 32 is controlled to a temperature at which the particulate matter trapped in the particulate filter 32 can be burned or higher, and the air-fuel ratio of the exhaust gas flowing into the particulate filter 32 is controlled to the lean side. Therefore, if filter regeneration control and abnormality diagnosis of the exhaust sensor 33 are performed simultaneously, even if the exhaust sensor 33 is operating normally, if the state value indicates a lean state due to the filter regeneration control, there is a risk of misdiagnosing an abnormality of the exhaust sensor 33. In order to prevent such a misdiagnosis of an abnormality of the exhaust sensor 33, it is possible to consider not performing abnormality diagnosis of the exhaust sensor 33 during filter regeneration control, but in this case, the frequency of detecting an abnormality of the exhaust sensor 33 decreases.

In contrast, the exhaust purification device 1 of this embodiment includes a three-way catalyst 31 that is provided in the exhaust passage 30 of the internal combustion engine 10 and purifies the exhaust gas discharged from the internal combustion engine 10, a particulate filter 32 that is provided in the exhaust passage 30 downstream of the three-way catalyst 31 and captures particulate matter in the exhaust, an exhaust sensor 33 that detects a state value related to the air-fuel ratio of the exhaust gas that has passed between the three-way catalyst 31 and the particulate filter 32, and a control unit that performs filter regeneration control to burn the particulate matter captured in the particulate filter 32 and regenerate the particulate filter 32 by controlling the air-fuel ratio in the exhaust passage 30 and upstream of the three-way catalyst 31 to a value greater than the theoretical air-fuel ratio when the amount of particulate matter accumulated in the particulate filter 32 is equal to or greater than a predetermined amount. Then, when the prerequisite for diagnosing the abnormality of the exhaust sensor 33 is met, the control unit prohibits filter regeneration control, and during the period when the filter regeneration control is prohibited, judges whether the exhaust sensor 33 is abnormal based on the response time of the exhaust sensor 33 from the start of fuel cut control that stops fuel injection of the internal combustion engine 10 until the state value reaches a predetermined value on the lean side from a specified air-fuel ratio that is equal to or lower than the theoretical air-fuel ratio.

In the exhaust purification device 1 configured in this manner, filter regeneration control is stopped when the prerequisites for performing an abnormality diagnosis of the exhaust sensor 33 are met. As a result, an abnormality diagnosis of the exhaust sensor 33 is performed from a state in which the filter regeneration control is stopped, so that it is possible to increase the frequency of detecting an abnormality in the exhaust sensor 33 while suppressing erroneous diagnosis of an abnormality in the exhaust sensor 33.

As described above, the exhaust purification device 1 according to this embodiment can increase the frequency with which an abnormality in the exhaust sensor 33 is detected. As a result, the accuracy of abnormality diagnosis of the exhaust sensor 33 is improved.

Reference Signs List 1 exhaust gas purification device 10 internal combustion engine 11 cylinder 12 piston 13 intake valve 14 exhaust valve 15 fuel injection valve 16 spark plug 17 water temperature sensor 20 intake passage 21 air filter 22 air flow meter 23 throttle valve 24 throttle sensor 30 exhaust passage 31 three-way catalyst 32 particulate filter 33 exhaust sensor 50 ECU
100 vehicles

Claims (1)

a three-way catalyst provided in an exhaust passage of an internal combustion engine and configured to purify exhaust gas discharged from the internal combustion engine;
a particulate filter provided in the exhaust passage downstream of the three-way catalyst and configured to collect particulate matter in the exhaust gas;
an exhaust sensor that detects a state value related to an air-fuel ratio of the exhaust gas that has passed between the three-way catalyst and the particulate filter;
a control unit that executes a filter regeneration control for burning the particulate matter trapped in the particulate filter by controlling an air-fuel ratio in the exhaust passage and upstream of the three-way catalyst to a value greater than a stoichiometric air-fuel ratio when a deposition amount of the particulate matter trapped in the particulate filter is equal to or greater than a predetermined amount, thereby regenerating the particulate filter;
having
The control unit is
prohibiting the filter regeneration control when a prerequisite for diagnosing an abnormality of the exhaust sensor is satisfied;
during execution of a fuel cut control for stopping fuel injection of the internal combustion engine, if the state value of the exhaust sensor before the start of the fuel cut control is a specified air-fuel ratio that is equal to or lower than a theoretical air-fuel ratio, during a period in which the filter regeneration control is prohibited, an abnormality of the exhaust sensor is determined based on a response time of the exhaust sensor from the start of the fuel cut control until the state value reaches a predetermined value on the lean side from the specified air-fuel ratio;
Exhaust purification device.

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