JP6339728B2 - Control device, exhaust purification device for internal combustion engine, and control method for exhaust purification device - Google Patents

Description

The present invention relates to a control device, an exhaust purification device for an internal combustion engine, and a control method for the exhaust purification device.

In some cases, exhaust gas discharged from an internal combustion engine mounted on a vehicle or the like contains nitrogen oxides (NOx). For this reason, for example, as described in Patent Document 1 below, an injection valve is disposed upstream of the selective reduction type NOx catalyst device (SCR), and the ammonia-based solution supplied from the ammonia-based solution supply device is injected into the injection valve. A system for reducing nitrogen oxides in exhaust gas by injecting into the exhaust gas passage is known.

Patent Document 2 below describes a technique in which a NOx sensor for measuring the NOx concentration of an exhaust gas flow of an internal combustion engine is calibrated at a selected operating point. Patent Document 3 below describes a technique for correcting the output of the NOx sensor based on the deviation between the output value of the NOx sensor and a reference output value preset according to the reference operating condition.

JP 2010-196552 A Special Table 2002-539448 JP 2009-127552 A

In the conventional system described in Patent Document 1, a NOx sensor is arranged downstream of the selective reduction type NOx catalyst device, and NOx and NH3 are detected by the NOx sensor, and this detected value is used. Feedback control is performed so that the exhaust gas discharged to the outside does not contain ammonia.

However, when NH3 is detected by a NOx sensor, it is difficult to detect an accurate NH3 concentration. For this reason, it is desirable to arrange an ammonia sensor downstream of the reduction catalyst to detect an accurate NH3 concentration.

On the other hand, when the ammonia sensor is used, if the detected value of the ammonia sensor does not indicate 0 when the actual NH 3 concentration is zero “0”, it is necessary to reset the zero point. In this regard, as described above, Patent Documents 2 and 3 describe techniques for correcting the output of the NOx sensor. However, in a system including a selective reduction type NOx catalyst device (SCR), ammonia generated by injecting an ammonia-based solution from the upstream side of the catalyst is adsorbed on the catalyst. For this reason, whether ammonia exists downstream of the catalyst has a close relationship with the injection control of the ammonia-based solution upstream of the catalyst, and it has been difficult to perform zero point reset in the same manner as the NOx sensor.

Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a zero ammonia sensor in a system including a reduction catalyst that adsorbs a reducing agent and reduces nitrogen oxides. It is an object of the present invention to provide a new and improved control device, an exhaust gas purification device for an internal combustion engine, and a control method for the exhaust gas purification device that can surely initialize the points.

In order to solve the above-described problem, according to an aspect of the present invention, the reducing agent is adsorbed under a condition in which the reducing agent does not flow out downstream of a reduction catalyst that adsorbs the reducing agent and reduces nitrogen oxides in exhaust gas. Based on an output value of the ammonia sensor acquired under the above conditions, an ammonia sensor output acquisition unit that acquires the output of an ammonia sensor provided downstream of the reduction catalyst, And a zero point diagnosis unit that diagnoses the zero point of the ammonia sensor, and a zero point initialization unit that initializes the zero point of the ammonia sensor based on a diagnosis result of the zero point diagnosis unit. Is provided.

The zero point diagnosis unit is based on the output value of the ammonia sensor acquired after the ammonia sensor is started at the time of starting the internal combustion engine and before the injection of the reducing agent to the reduction catalyst is started. The zero point of the ammonia sensor may be diagnosed.

The zero point diagnosis unit may diagnose the zero point of the ammonia sensor based on an output value of the ammonia sensor acquired during normal operation in which the reducing agent is injected into the reduction catalyst. good.

The zero point diagnosis unit may diagnose the zero point of the ammonia sensor based on the output value of the ammonia sensor acquired when the catalyst temperature of the reduction catalyst decreases.

In addition, the reducing agent injection control unit temporarily reduces the amount of the reducing agent injected to the reduction catalyst when the zero point diagnosis unit diagnoses the zero point of the ammonia sensor. May be.

Further, the reducing agent injection control unit determines the amount of the reducing agent injected to the reduction catalyst from a value based on the target adsorption amount of the reduction catalyst during normal operation, which is smaller than the target adsorption amount. The value may be reduced to a value based on.

The reducing agent injection control unit temporarily stops the injection of the reducing agent to the reduction catalyst when the zero point diagnosis of the ammonia sensor is performed by the zero point diagnosis unit. Also good.

In addition, an adsorption amount estimation unit that estimates an adsorption amount of the reducing agent in the reduction catalyst is provided, and the zero point diagnosis unit is configured to perform the diagnostic adsorption in which the adsorption amount is smaller than the target adsorption amount of the reduction catalyst during normal operation. The zero point of the ammonia sensor may be diagnosed based on the output value of the ammonia sensor acquired when the amount is less than the amount.

The zero point diagnosis unit may diagnose the zero point of the ammonia sensor based on an average value of the output values of the ammonia sensor acquired during a specified time.

The zero point initialization unit may initialize the zero point of the ammonia sensor when the output value of the ammonia sensor acquired under the conditions is equal to or greater than a predetermined allowable value.

In order to solve the above problems, according to an aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine including the above-described control device.

In order to solve the above-described problem, according to an aspect of the present invention, the reducing agent is adsorbed by reducing the nitrogen oxide in the exhaust gas by adsorbing the reducing agent, and the reducing agent does not flow out downstream. Based on the step of controlling the injection of the reducing agent, the step of obtaining the output of the ammonia sensor provided downstream of the reduction catalyst, and the output value of the ammonia sensor obtained under the conditions, There is provided a control method for an exhaust gas purification apparatus, comprising: diagnosing a zero point; and initializing a zero point of the ammonia sensor based on a diagnosis result of the zero point.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to initialize the zero point of an ammonia sensor reliably in the system provided with the reduction catalyst which adsorb | sucks a reducing agent and reduces nitrogen oxides.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of an internal combustion engine exhaust purification apparatus and its peripheral configuration according to an embodiment of the present invention. It is the block diagram which represented the process which concerns on the offset diagnosis of the zero point of the ammonia sensor 14, and a zero point reset among the structures of the control apparatus with which the exhaust gas purification device of this embodiment was equipped. It is a flowchart which shows the process of the 1st method of the zero point reset of the ammonia sensor which concerns on this embodiment. It is a flowchart which shows the process of the 1st method of the zero point reset of the ammonia sensor which concerns on this embodiment. It is a characteristic view which shows the relationship between target NH3 adsorption amount and NH3 adsorption amount for diagnosis. It is a flowchart which shows the process of the 2nd method of the zero point reset of the ammonia sensor which concerns on this embodiment. It is a flowchart which shows the process of the 2nd method of the zero point reset of the ammonia sensor which concerns on this embodiment. It is a flowchart which shows the process of the 3rd method of the zero point reset of the ammonia sensor which concerns on this embodiment. It is a flowchart which shows the process of the 3rd method of the zero point reset of the ammonia sensor which concerns on this embodiment.

Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

1. Exhaust Purification Device (1) Overall Configuration FIG. 1 shows an example of the configuration of an exhaust purification device 10 for an internal combustion engine according to one embodiment of the present invention and its surroundings. This exhaust purification device 10 is connected to the exhaust passage 11 of the internal combustion engine 5, and includes a reduction catalyst 20, a reducing agent injection device 30, a control device 60 and the like, and exhaust gas discharged from the internal combustion engine 5. It is configured as a urea SCR system that purifies nitrogen oxide (NOx) therein using a urea aqueous solution as a reducing agent. However, the reducing agent that can be used in the present embodiment is not limited to the urea aqueous solution, and may be any one that generates ammonia, such as ammonia water.

The internal combustion engine 5 is controlled by an ECU (Engine Control Unit) 50. The control device 60 receives control data related to the control of the internal combustion engine 5 from the ECU 50. In the exhaust passage 11, an oxidation catalyst 12 (DOC) is disposed between the internal combustion engine 5 and the reduction catalyst 20. The oxidation catalyst 12 has a function of oxidizing hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas. A known catalyst is appropriately used as the oxidation catalyst 12.

The reduction catalyst 20 used in the exhaust purification device 10 of the present embodiment has a function of adsorbing ammonia generated by the decomposition of the aqueous urea solution injected into the exhaust passage 11 and promoting the reduction reaction between ammonia and NOx. have. Specifically, in the reduction catalyst 20, ammonia (NH3) produced by the decomposition of urea in the urea aqueous solution reacts with NOx, whereby NOx is decomposed into nitrogen (N2) and water (H2O). . A known catalyst is appropriately used as the reduction catalyst 20.

An ammonia sensor (NH 3 sensor) 14 for detecting the ammonia (NH 3) concentration in the exhaust gas is provided on the downstream side of the reduction catalyst 20. Further, a NOx sensor 16 for detecting the NOx concentration in the exhaust gas is provided on the upstream side of the reduction catalyst 20. The sensor signal of the ammonia sensor 14 is transmitted to the control device 60, and the control device 60 calculates the ammonia concentration in the exhaust gas based on this sensor signal. Further, the sensor signal of the NOx sensor 16 is transmitted to the control device 60, and the control device 60 calculates the NOx concentration in the exhaust gas based on this sensor signal. An exhaust temperature sensor 18 that detects the temperature of the exhaust gas is provided upstream of the reduction catalyst 20.

(2) Reducing agent injection device The reducing agent injection device 30 is mainly configured by a storage tank 31, a reducing agent injection valve 34, a pump 41, and the like. The storage tank 31 and the pump 41 are connected by a first reducing agent supply passage 57, and the pump 41 and the reducing agent injection valve 34 are connected by a second reducing agent supply passage 58. Among these, the pressure sensor 43 is provided in the second reducing agent supply passage 58. The sensor signal of the pressure sensor 43 is transmitted to the control device 60, and the control device 60 calculates the pressure in the second reducing agent supply passage 58 based on this sensor signal.

Further, a circulation passage 59 that leads to the storage tank 31 is connected to the second reducing agent supply passage 58. The circulation passage 59 is provided with an orifice 45 so as to provide resistance to the flow of the reducing agent returned to the storage tank 31 through the circulation passage 59 and to increase the pressure in the second reducing agent supply passage 58. It has become. As such a reducing agent injection device itself, one having a known configuration can be used.

An electric pump that is driven and controlled by the control device 60 is used as the pump 41. In the present embodiment, the pump 41 is configured such that its output is feedback-controlled so that the pressure in the second reducing agent supply passage 58 detected by the pressure sensor 43 is maintained at a predetermined value. .

The reducing agent injection valve 34 is an electromagnetically driven on / off valve whose opening / closing is controlled by the control device 60, and is fixed to the exhaust passage 11 upstream of the reducing catalyst 20. The reducing agent injection valve 34 is basically energized and controlled while the pressure in the second reducing agent supply passage 58 is maintained at the target value. Specifically, the injection amount of the reducing agent into the exhaust passage 11 is adjusted by setting the valve opening DUTY ratio during a predetermined DUTY cycle according to the command injection amount Q obtained by calculation.

Here, the command injection amount Q of the reducing agent injection valve 34 can be calculated from the following equation (1).
Instructed injection amount Q = (injection amount A corresponding to the current NOx flow rate) + (injection amount B corresponding to the adsorbable amount of the reduction catalyst)
... (1)

In equation (1), the injection amount A corresponding to the current NOx flow rate is the injection amount corresponding to the NOx flow rate in the exhaust gas flowing upstream of the reduction catalyst 20, and in the exhaust gas flowing upstream of the reduction catalyst 20. This is the injection amount necessary to reduce the NOx. The NOx flow rate in the exhaust gas flowing upstream of the reduction catalyst 20 can be obtained by multiplying the exhaust gas flow rate by the NOx concentration calculated from the sensor signal of the NOx sensor 16. The amount injected excessively than the injection amount A corresponding to the NOx flow rate in the exhaust gas corresponds to the amount adsorbed by the reduction catalyst 20 (ammonia adsorption amount) at that time, and the amount injected excessively (injection amount B). ) Is controlled so as to be an amount capable of being adsorbed by the reduction catalyst. In addition, the injection amount B corresponding to the adsorbable amount of the reduction catalyst 20 is calculated from the total adsorption amount (corresponding to a target NH3 adsorption amount described later) that the reduction catalyst 20 can adsorb at the current catalyst temperature. This is an amount calculated from the difference obtained by subtracting the ammonia adsorption amount of the catalyst 20. The amount of adsorption that can be adsorbed by the reduction catalyst 20 is determined in advance from the characteristics of the reduction catalyst 20, and varies depending on the catalyst temperature. The total adsorption amount that can be adsorbed by the reduction catalyst 20 is set to a value of about 80% with respect to the maximum adsorption amount that the reduction catalyst 20 can theoretically adsorb. Thereby, the ammonia adsorption amount of the reduction catalyst 20 is not saturated, and the outflow of ammonia downstream can be suppressed.

The control device 60 calculates the command injection amount Q from the above equation for each predetermined cycle, and controls the injection amount of the reducing agent injection valve 34. The control device 60 calculates the injection amount B corresponding to the amount of catalyst that can be adsorbed for each predetermined cycle, and integrates it with the value of the injection amount B obtained in the previous cycle, so that the control device 60 calculates the injection amount B every predetermined cycle. The ammonia adsorption amount of the reduction catalyst 20 can be acquired.

2. Specific Method for Ammonia Sensor Zero Point Reset Next, the offset diagnosis for detecting the zero point drift of the sensor signal of the ammonia sensor 14 will be described in detail. The control device 60 determines whether ammonia (NH 3) is contained in the exhaust gas based on the output signal of the ammonia sensor 14. And when ammonia (NH3) is contained in exhaust gas, by reducing the injection amount of the reducing agent injection valve 34, ammonia is suppressed from being released into the atmosphere through the reduction catalyst 20.

It is assumed that the NH3 concentration detected from the ammonia sensor 14 is offset from the original NH3 concentration value. For this reason, in order to detect the exact NH3 concentration in the exhaust gas, the zero point reset of the ammonia sensor 14 is performed. The zero point reset is to reset the NH3 concentration detected from the ammonia sensor 14 to zero “0” in a state where NH3 is not contained in the exhaust gas. Thereby, after the zero point reset is performed, it is possible to detect the correct NH 3 concentration from the output signal of the ammonia sensor 14.

The zero point reset of the ammonia sensor 14 is performed in a situation where NH 3 does not flow out downstream of the reduction catalyst 20. Specifically, the following first to third methods cause a situation in which NH3 does not flow downstream of the reduction catalyst 20, and the zero point offset diagnosis of the ammonia sensor 14 is performed. If the zero point of the ammonia sensor 14 is offset as a result of the offset diagnosis, the zero point is reset.

In the first method, the zero point offset diagnosis is performed after the ammonia sensor 14 is started when the internal combustion engine 5 is started and before the injection of the reducing agent from the reducing agent injection valve 34 is started. While the injection from the reducing agent injection valve 34 is not started, the ammonia NH 3 does not flow into the exhaust passage 11, so basically the ammonia NH 3 does not flow downstream of the reduction catalyst 20. For this reason, the offset diagnosis of the zero point of the output of the ammonia sensor 14 can be performed. Note that while the injection from the reducing agent injection valve 34 is not performed, NOx contained in the exhaust gas is reduced by the ammonia already adsorbed by the reduction catalyst 20.

When the internal combustion engine 5 is started, the injection of the reducing agent from the reducing agent injection valve 34 is started after the exhaust gas in the exhaust passage 11 rises to a temperature at which the reducing agent can be decomposed. Therefore, since the reducing agent is not injected into the exhaust passage 11 after the internal combustion engine 5 is started and before the exhaust temperature rises to a temperature at which the reducing agent can be decomposed, the zero point offset diagnosis of the ammonia sensor 14 is performed. Can do.

In the first method, preferably, the zero point offset diagnosis is performed when the ammonia adsorption amount of the reduction catalyst 20 is equal to or less than a predetermined value. Thereby, it is possible to reliably prevent ammonia from flowing out downstream of the reduction catalyst 20, and it is possible to perform the offset diagnosis of the zero point with higher accuracy.

In the second method, when the reducing agent is injected from the reducing agent injection valve 34 in a normal operation state, the amount of adsorption of ammonia in the reduction catalyst 20 is small and ammonia does not flow downstream of the reduction catalyst 20. Perform zero point offset diagnosis with.

In the second method, preferably, the offset diagnosis is performed by reducing the injection amount of the reducing agent from the normal time. Thereby, it is possible to reliably prevent ammonia from flowing out downstream of the reduction catalyst 20, and it is possible to perform the offset diagnosis of the zero point with higher accuracy.

In the third method, the zero point offset diagnosis is performed when the temperature of the reduction catalyst 20 transitions from a high temperature to a low temperature. When the temperature of the reduction catalyst 20 transitions from a high temperature to a low temperature, the amount of ammonia that can be adsorbed by the reduction catalyst 20 increases, so that the ammonia is suppressed from flowing downstream of the reduction catalyst 20. Therefore, by performing the zero point offset diagnosis at the timing when the temperature of the reduction catalyst 20 transitions from the high temperature to the low temperature, ammonia does not flow downstream of the reduction catalyst 20, and the zero point offset diagnosis can be performed.

Also in the third method, preferably, the offset diagnosis is performed by reducing the injection amount of the reducing agent from the normal time. Thereby, it is possible to reliably prevent ammonia from flowing out downstream of the reduction catalyst 20, and it is possible to perform the offset diagnosis of the zero point with higher accuracy.

If the zero point of the ammonia sensor 14 is shifted as a result of the zero point offset diagnosis, the zero point is reset. Thereby, the ammonia sensor 14 that has performed the zero point reset can accurately detect the ammonia concentration downstream of the reduction catalyst 20. Therefore, the reducing agent injection amount from the reducing agent injection valve 34 can be feedback-controlled with high accuracy based on the ammonia concentration obtained from the output signal of the ammonia sensor 14.

2. FIG. 2 is a functional block diagram showing processing relating to zero point offset diagnosis and zero point reset of the ammonia sensor 14 in the configuration of the control device 60 provided in the exhaust purification device 10 of the present embodiment. It is a thing. The control device 60 includes an ammonia sensor output acquisition unit 62, a zero point diagnosis unit 64, a zero point initialization unit 66, an exhaust temperature acquisition unit 68, a reducing agent injection control unit 70, a determination unit 72, and an adsorption amount estimation unit 72. Configured. The control device 60 is mainly configured by a microcomputer having a known configuration, and each component is realized by execution of a program by the microcomputer.

In addition, the control device 60 includes a storage unit (not shown). The storage unit stores calculation results for each component, a data map prepared in advance, and the like. The storage unit is composed of a volatile memory (RAM: Random Access Memory) or a nonvolatile memory.

The ammonia sensor output acquisition unit 62 acquires the output of the ammonia sensor 14 provided downstream of the reduction catalyst 20. The zero point diagnosis unit 64 diagnoses the zero point of the ammonia sensor 14 based on the output value of the ammonia sensor 14 acquired under the condition that the reducing agent does not flow downstream of the reduction catalyst 20. The zero point initialization unit 66 initializes (resets) the zero point of the ammonia sensor 14 based on the diagnosis result of the zero point diagnosis unit 64. The exhaust temperature acquisition unit 68 acquires the temperature of the exhaust gas flowing through the exhaust passage 11 from the output of the exhaust temperature sensor 18. The reducing agent injection control unit 70 controls the injection of the reducing agent from the reducing agent injection valve 34 based on the instruction injection amount Q according to the above-described equation (1). Further, when performing the zero point offset diagnosis, the reducing agent injection control unit 70 performs control to reduce the injection amount and stop the injection as described later. The adsorption amount estimation unit 72 estimates the ammonia adsorption amount in the reduction catalyst 20 by integrating the injection amount B corresponding to the adsorbable amount of the above-described equation (1).

Next, specific processing performed by the control device 60 for each of the first to third methods described above will be described. 3 and 4 are flowcharts showing the processing of the first method. First, in step S10 of FIG. 3, the value of the ammonia sensor 14 is read. In the next step S12, it is determined whether or not the ammonia sensor 14 can be activated. If the ammonia sensor 14 can be activated, the process proceeds to the next step S14. On the other hand, if the ammonia sensor 14 cannot be activated, the process waits in step S12.

In step S14, the ammonia sensor 14 is activated. In the next step S16, it is determined whether or not the activation of the ammonia sensor 14 is completed. If the activation is completed, the process proceeds to the next step S18. On the other hand, when the activation of the ammonia sensor 14 is not completed, the process waits in step S16.

In step S <b> 18, it is determined whether urea water can be injected from the reducing agent injection valve 34. When the urea water can be injected, the process proceeds to the next step S20, where the reducing agent is injected from the reducing agent injection valve 34 and the normal operation is performed. Here, whether or not urea water can be injected is determined based on whether or not the exhaust temperature has reached a temperature at which urea water can be decomposed.

If the urea water injection from the reducing agent injection valve 34 is not possible in step S18, the process proceeds to step S22 in FIG. In step S22, it is determined whether or not the estimated NH3 adsorption amount of the reduction catalyst 20 is smaller than the diagnostic NH3 adsorption amount. If the estimated NH3 adsorption amount is smaller than the diagnostic NH3 adsorption amount, the process proceeds to step S24. Here, the estimated NH3 adsorption amount can be obtained by integrating the injection amount B corresponding to the adsorbable amount of the above-described equation (1), and the previous integration result for each injection amount calculation in each duty cycle. In this case, the present adsorbable amount equivalent amount B is integrated and stored in the memory. The diagnostic NH3 adsorption amount is a value set in advance according to the catalyst temperature. On the other hand, if the estimated NH3 adsorption amount is greater than or equal to the diagnostic NH3 adsorption amount, the process returns to step S18.

FIG. 5 is a characteristic diagram showing the relationship between the target NH3 adsorption amount and the diagnostic NH3 adsorption amount. In FIG. 4, the horizontal axis represents the catalyst temperature of the reduction catalyst 20, and the vertical axis represents the NH 3 adsorption amount of the reduction catalyst 20. The ammonia adsorption amount of the reduction catalyst 20 changes according to the catalyst temperature, and the ammonia adsorption amount increases as the catalyst temperature decreases. Therefore, as shown in FIG. 4, the target NH3 adsorption amount is set to increase as the catalyst temperature decreases. During normal operation, injection from the reducing agent injection valve 34 is performed based on the catalyst temperature of the reduction catalyst 20 so that the ammonia adsorption amount of the reduction catalyst 20 becomes the target NH3 adsorption amount. As described above, the target NH3 adsorption amount is set to about 80% of the amount that the reduction catalyst 20 can adsorb at each temperature.

As shown in FIG. 5, the diagnostic NH3 adsorption amount is set to a value smaller than the target NH3 adsorption amount, and is set so that the difference from the target NH3 adsorption amount increases as the catalyst temperature decreases. The diagnostic NH3 adsorption amount is set to a value at which the outflow of ammonia downstream of the reduction catalyst 20 becomes zero when the ammonia adsorption amount of the reduction catalyst 20 is smaller than the diagnostic NH3 adsorption amount. Therefore, when the ammonia adsorption amount is smaller than the diagnostic NH3 adsorption amount, the zero point reset of the ammonia sensor 14 is performed, so that the output of the ammonia sensor 14 is reset to “0” in a situation where ammonia is not detected. Point reset can be performed with high accuracy.

Returning to FIG. 4, in step S24, the output value of the ammonia sensor 14 is integrated. In the next step S26, it is determined whether or not the specified time has elapsed. If the specified time has elapsed, the process proceeds to step S28, where the integrated value of the output of the ammonia sensor 14 is averaged over the specified time, and the average NH3 Calculate the concentration. On the other hand, if the specified time has not elapsed, the process returns to step S18.

In step S30, it is determined whether or not the average NH3 concentration is smaller than a predetermined tolerance (tolerance). If the average NH3 concentration is smaller than the tolerance, normal operation is performed in step S32. On the other hand, if the average NH3 concentration is greater than or equal to tolerance in step S30, the process proceeds to step S34, and zero point adjustment is performed based on the average NH3 concentration. Specifically, the zero point is reset so that the average NH 3 concentration value becomes “0”. After step S30, the process proceeds to step S32, and normal operation is performed based on the sensor value for which zero point adjustment has been performed.

The tolerance value is determined by the detection error of the ammonia sensor 14 itself. In step S30, when the average NH3 concentration is smaller than the tolerance, it is considered that a shift from the zero value is caused by the detection error of the ammonia sensor 14 itself, so the zero point adjustment in step S34 is not performed.

As described above, according to the processing of FIGS. 3 and 4, when the estimated NH3 adsorption amount is smaller than the diagnostic NH3 adsorption amount immediately after the start of the ammonia sensor 14, such as immediately after the internal combustion engine 5 is started, the ammonia sensor The average NH3 concentration is calculated from the 14 output values. Here, when the estimated NH 3 adsorption amount is smaller than the diagnostic NH 3 adsorption amount, a sufficient amount of ammonia is not adsorbed on the reduction catalyst 20, and ammonia does not flow downstream of the reduction catalyst 20. Therefore, by resetting the average NH3 concentration calculated under the condition that ammonia does not flow out downstream of the reduction catalyst 20 to 0, the zero point can be reset with high accuracy.

6 and 7 are flowcharts showing the processing of the second method. First, in step S40 in FIG. 6, the value of the ammonia sensor 14 is read. In the next step S42, it is determined whether or not the catalyst temperature of the reduction catalyst 20 is higher than 200 ° C. If the catalyst temperature is higher than 200 ° C, the process proceeds to step S44. On the other hand, when the catalyst temperature is 200 ° C. or lower, the process waits in step S42. The significance of determining whether or not the catalyst temperature is higher than 200 ° C. is to determine whether or not the reduction catalyst 20 is in an activated state and is capable of performing urea water injection control. . That is, when the diagnosis becomes unnecessary in the next step S44, normal operation is performed, and urea water injection control is performed because the catalyst temperature is higher than 200 ° C.

In step S44, it is determined whether or not the zero point offset diagnosis of the ammonia sensor 14 is necessary. When the zero point offset diagnosis is performed, the process proceeds to step S46. On the other hand, when the zero point offset diagnosis is not performed, the process proceeds to step S48, and the normal operation is performed.

At the time of determination in step S44, for example, when the total travel distance or total travel time of the vehicle on which the exhaust gas purification device 10 is mounted reaches a predetermined value, or when a specified time has elapsed during operation of the vehicle. It is determined that zero point offset diagnosis is performed.

In step S46, the urea water injection from the reducing agent injection valve 34 is stopped. As a result, NOx in the exhaust gas is reduced by the ammonia adsorbed on the reduction catalyst 20, and the amount of ammonia adsorbed on the reduction catalyst 20 decreases. In step S46, the injection amount may be decreased without completely stopping the injection. For example, the injection amount may be reduced to a normal level of about 60 to 70%. Thus, it is possible to reduce the amount of ammonia adsorbed on the reduction catalyst 20 even when the injection amount is reduced.

In the next step S50, it is determined whether or not the estimated NH3 adsorption amount of the reduction catalyst 20 is smaller than the diagnostic NH3 adsorption amount. If the estimated NH3 adsorption amount is smaller than the diagnostic NH3 adsorption amount, step S52 in FIG. Proceed to

In step S52, injection of urea water is started by injection control based on the diagnostic NH3 adsorption amount. That is, the reducing agent is injected from the reducing agent injection valve 34 so that the ammonia adsorption amount of the reduction catalyst 20 becomes the NH3 adsorption amount for diagnosis. In the next step S54, the output value of the ammonia sensor 14 is integrated. In the next step S56, it is determined whether or not the specified time has passed. If the specified time has passed, the process proceeds to step S58, and the integrated value of the output of the ammonia sensor 14 is averaged over the specified time to obtain an average NH3 concentration. Is calculated. On the other hand, if the specified time has not elapsed, the process waits in step S56.

In step S60, it is determined whether or not the average NH3 concentration is smaller than a predetermined tolerance. If the average NH3 concentration is smaller than the tolerance, normal operation is performed in step S62. On the other hand, if the average NH3 concentration is greater than or equal to tolerance in step S60, the process proceeds to step S64, and zero point adjustment is performed based on the average NH3 concentration.

As described above, according to the processing of FIGS. 6 and 7, when the catalyst temperature exceeds 200 ° C. during the operation of the internal combustion engine 5, the injection from the reducing agent injection valve 34 is stopped or reduced and estimated. When the NH3 adsorption amount becomes smaller than the diagnostic NH3 adsorption amount, the reducing agent is injected so that the ammonia adsorption amount of the reduction catalyst 20 becomes the diagnostic NH3 adsorption amount. Here, by performing injection with the NH3 amount for diagnosis used as the target ammonia adsorption amount of the reduction catalyst 20, a sufficient amount of ammonia is not adsorbed on the reduction catalyst 20, and ammonia flows out downstream of the reduction catalyst 20. There is nothing to do. Therefore, by resetting the average NH3 concentration calculated under the condition that ammonia does not flow out downstream of the reduction catalyst 20 to 0, the zero point can be reset with high accuracy.

6 and 7 are preferably performed in a temperature range in which ammonia does not flow downstream of the reduction catalyst 20 even when a temperature change occurs. For example, the catalyst temperature is about 200 ° C. to 300 ° C. It is desirable to implement in the range. Thereby, when the catalyst temperature becomes higher, it is possible to prevent the ammonia adsorption amount of the reduction catalyst 20 from decreasing and the ammonia from flowing downstream of the reduction catalyst 20.

8 and 9 are flowcharts showing the third method. First, in step S70 in FIG. 8, the value of the ammonia sensor 14 is read. In the next step S72, it is determined whether or not the catalyst temperature of the reduction catalyst 20 is higher than 400 ° C. If the catalyst temperature is higher than 400 ° C, the process proceeds to step S74. On the other hand, when the catalyst temperature is equal to or lower than 400 ° C., the process proceeds to step S78 to perform normal operation.

In step S74, it is determined whether or not the zero point offset diagnosis of the ammonia sensor 14 is necessary. When the zero point offset diagnosis is performed, the process proceeds to step S76. On the other hand, when the zero point offset diagnosis is not performed, the process proceeds to step S78 and normal operation is performed. This determination can be made in the same manner as in the second method.

In step S76, it is determined whether or not the temperature of the reduction catalyst 20 has decreased. If the temperature of the reduction catalyst 20 has decreased, the process proceeds to step S78. On the other hand, if the temperature of the reduction catalyst 20 has not decreased, the process stands by in step S76.

In step S78, injection is performed by switching the target value of the injection amount from the reducing agent injection valve 34 from the normal target NH3 adsorption amount to the diagnostic NH3 adsorption amount. As a result, as shown in FIG. 5, in the case of a normal target NH3 adsorption amount, the injection amount is greatly increased as the catalyst temperature decreases, but by switching the target value to the diagnostic NH3 adsorption amount, The increase in the injection amount accompanying the decrease in temperature is alleviated. Therefore, it is possible to reliably prevent ammonia from flowing out downstream of the reduction catalyst 20.

After step S78, the process proceeds to step S80 in FIG. 9, and the output value of the ammonia sensor 14 is integrated. In the next step S82, it is determined whether or not the specified time has passed. If the specified time has passed, the process proceeds to step S84, and the integrated value of the output of the ammonia sensor 14 is averaged over the specified time to obtain an average NH3 concentration. Is calculated. On the other hand, if the specified time has not elapsed, the process waits in step S82.

In step S86, it is determined whether or not the average NH3 concentration is smaller than tolerance. If the average NH3 concentration is smaller than tolerance, normal operation is performed in step S88. On the other hand, if the average NH3 concentration is greater than or equal to tolerance in step S86, the process proceeds to step S90, and zero point adjustment based on the average NH3 concentration is performed.

As described above, according to the processing of FIGS. 8 and 9, when the catalyst temperature exceeds 400 ° C. and the temperature of the reduction catalyst 20 is decreased, the injection amount from the reducing agent injection valve 34. The target value is switched from the normal target NH3 adsorption amount to the diagnostic NH3 adsorption amount, and injection is performed. As a result, the ammonia adsorption amount of the reduction catalyst 20 increases due to a decrease in temperature, so that ammonia can be prevented from flowing downstream of the reduction catalyst 20, and the normal target NH3 adsorption amount is switched to the diagnostic NH3 adsorption amount. Therefore, it is possible to reliably prevent ammonia from flowing out downstream of the reduction catalyst 20.

As described above, according to the present embodiment, since the zero point diagnosis of the ammonia sensor 14 is performed under the condition where ammonia does not flow out downstream of the reduction catalyst 20, the zero point diagnosis of the ammonia sensor can be accurately performed. It becomes possible.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Exhaust gas purification apparatus 20 Reduction catalyst 34 Reducing agent injection valve 60 Control apparatus 62 Ammonia sensor output acquisition part 64 Zero point diagnostic part 66 Zero point initialization part 70 Reducing agent injection control part 72 Adsorption amount estimation part

Claims (5)

A reducing agent injection control unit that controls injection of the reducing agent under a condition in which the reducing agent does not flow downstream of a reduction catalyst that adsorbs the reducing agent and reduces nitrogen oxides in the exhaust gas;
An ammonia sensor output acquisition unit for acquiring an output of an ammonia sensor provided downstream of the reduction catalyst;
Based on the output value of the ammonia sensor acquired under the conditions, a zero point diagnosis unit that diagnoses the zero point of the ammonia sensor;
Based on the diagnosis result of the zero point diagnosis unit, a zero point initialization unit that initializes the zero point of the ammonia sensor;
An adsorption amount estimation unit for estimating the amount of adsorption of the reducing agent in the reduction catalyst;
With
The zero point diagnosis unit is configured to reduce the adsorption amount during normal operation until the start of the injection of the reducing agent to the reduction catalyst after the ammonia sensor is started when the internal combustion engine is started. A control device for diagnosing the zero point of the ammonia sensor based on the acquired output value of the ammonia sensor when the amount is less than the target adsorption amount less than the target adsorption amount.   The control according to claim 1, wherein the zero point diagnosis unit diagnoses a zero point of the ammonia sensor based on an average value of the output values of the ammonia sensor acquired during a specified time. apparatus.   The zero point initialization unit initializes the zero point of the ammonia sensor when the output value of the ammonia sensor acquired under the conditions is equal to or greater than a predetermined allowable value. 2. The control device according to 2.   An exhaust emission control device for an internal combustion engine, comprising the control device according to claim 1. Controlling injection of the reducing agent under conditions where the reducing agent does not flow downstream of a reduction catalyst that adsorbs the reducing agent to reduce nitrogen oxides in the exhaust gas; and
Obtaining an output of an ammonia sensor provided downstream of the reduction catalyst;
Diagnosing the zero point of the ammonia sensor based on the output value of the ammonia sensor acquired under the conditions;
Initializing the zero point of the ammonia sensor based on the diagnostic result of the zero point;
Estimating the amount of adsorption of the reducing agent on the reduction catalyst;
With
In the step of diagnosing the zero point, after the ammonia sensor is started at the time of starting the internal combustion engine, the amount of adsorption is the time during normal operation until the injection of the reducing agent to the reduction catalyst is started. An exhaust purification device characterized by diagnosing the zero point of the ammonia sensor based on the acquired output value of the ammonia sensor when the amount is less than the target adsorption amount of the reduction catalyst and less than the target adsorption amount. Control method.

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