US20120031077A1

US20120031077A1 - Pm sensor, pm amount sensing device for exhaust gas, and abnormality detection apparatus for internal combustion engine

Info

Publication number: US20120031077A1
Application number: US13/147,515
Authority: US
Inventors: Keiichiro Aoki
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2009-04-27
Filing date: 2009-04-27
Publication date: 2012-02-09
Also published as: JPWO2010125636A1; DE112009004746T5; WO2010125636A1; JP5196012B2; DE112009004746B4; CN102414551A

Abstract

Provided is a PM sensor capable of sensing the amount of particulate matter, and a PM amount sensing device for exhaust gas. Also provided is an abnormality detection apparatus for an internal combustion engine, which is capable of sensing abnormality of a particulate filter. The PM sensor and the PM amount sensing device are mounted in an exhaust pipe of an internal combustion engine. In the exhaust pipe, installed are an air-fuel ratio sensor, a filter, and an air-fuel ratio sensor in sequence in the direction of the flow of exhaust gas. The filter is a compact filter for trapping fine particles. The ECU has a function of calculating a difference ΔI_Lbetween an output I_L1and an output I_L2. Based on ΔI_L, it is possible to calculate the amount of particulate matter in the exhaust gas that is currently flowing into the filter.

Description

TECHNICAL FIELD

The present invention relates to a PM sensor, a PM amount sensing device for exhaust gas, and an abnormality detection apparatus for an internal combustion engine.

BACKGROUND ART

Conventionally, as disclosed in, for example, Japanese Patent Laid-Open No. 08-284644, there is known an internal combustion engine equipped with a particulate filter for filtering particulate matter in the exhaust gas. Hereinafter, the particulate matter is also referred to simply as “particulates”, or “PM”.
The conventional internal combustion engine described above is equipped with a pressure sensor for detecting a differential pressure of a filter. When exhaust gas containing a large amount of particulates flows into a filter, the amount of particulates in the filter increases accordingly. The differential pressure of the filter also changes following that as well. Therefore, by sensing the differential pressure of the filter, it is possible to sense the amount of particulates in the exhaust gas.
Besides, as the configuration for sensing the amount of particulates, the configurations of Japanese Patent Laid-Open No. 2007-32490 and Japanese Patent Laid-open No. 2008-64621 are well known.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 08-284644
Patent Literature 2: Japanese Patent Laid-Open No. 2007-32490
Patent Literature 3: Japanese Patent Laid-open No. 2008-64621

SUMMARY OF INVENTION

Technical Problem

As exhaust emission regulations have been tightened in recent years, there is a growing need for sensors for sensing the amount of particulates. At the current technological level, however, there is no advent of on-board type PM sensor or PM amount sensing device, which can withstand practical use environments. Thus, there are urgent needs for developments of PM sensors and PM amount sensing devices for sensing the amount of particulates. Moreover, when an abnormality occurs in a particulate filter of an internal combustion engine, an immediate countermeasure needs to be taken. Thus, technological advancements are also desired in the abnormality sensing technique for particulate filters.
The present invention has been made to solve the above described problems, and has an object to provide a PM sensor and a PM amount sensing device for exhaust gas, which are capable of sensing the amount of particulate matter.
It is another object of the present invention to provide an abnormality detection apparatus for an internal combustion engine, which is capable of detecting abnormality of a particulate filter.

Solution to Problem

To achieve the above-mentioned purpose, a first aspect of the present invention is a PM sensor, comprising:
an inlet port through which a portion of gas that is drawn from an exhaust path of an internal combustion engine is allowed to flow in;
a filter for filtering particulate matter (PM) in the gas that has flowed in through the inlet port;
a heater attached to the filter and capable of changing the temperature of the filter;
an outlet port through which the gas that has passed through the filter is allowed to flow out to the exhaust path; and
an oxygen concentration sensor element disposed in the outlet port side and adapted to change its output according to an oxygen concentration of the gas that has passed through the filter.
A second aspect of the present invention is the PM sensor according to the first aspect, further comprising
an oxygen concentration sensor element disposed between the inlet port and the filter and adapted to change its output according to an oxygen concentration of gas that has flowed in through the inlet port.
A third aspect of the present invention is the PM sensor according to the second aspect, wherein
the oxygen concentration sensor element of the outlet port side and the oxygen concentration sensor element of the inlet port side are air-fuel ratio sensor elements.
A fourth aspect of the present invention is the PM sensor according to the third aspect, wherein
the air-fuel ratio sensor element includes a heater and upon being activated, is heated to a predetermined temperature by the heater, and
the filter and the air-fuel ratio sensor element are spaced apart such that the filter comes to a level of temperature at which particulate matter in the filter is not removed when the temperature of the air-fuel ratio sensor element is at the predetermined temperature.
To achieve the above-mentioned purpose, a fifth aspect of the present invention is a PM amount sensing device for exhaust gas, comprising:
a filter provided in an exhaust path of an internal combustion engine and for filtering particulate matter (PM) in exhaust gas that flows through the exhaust path;
an oxygen concentration sensor element disposed in a downstream of the filter in the exhaust path, and adapted to change its output according to an oxygen concentration of the gas that has passed through the filter;
a heater attached to the filter;
heating control means for controlling the heater such that the filter is heated until particulate matter in the filter is removed;
temperature reduction control means for controlling the heater such that a temperature of the filter is not higher than a temperature at which particulate matter in the filter is not removed, after the control of the heating control means;
acquisition means for acquiring an output of the oxygen concentration sensor element after a temperature of the filter becomes not higher than the temperature; and
calculation means for calculating an amount of particulate matter in the exhaust gas based on the output acquired by the acquisition means.
A sixth aspect of the present invention is the PM amount sensing device for exhaust gas according to the fifth aspect, wherein
the acquisition means includes means for acquiring an output of the oxygen concentration sensor element when a predetermined time period has elapsed after a temperature of the filter has become not higher than the temperature, and calculating an integrated value of an amount of exhaust gas that has flowed into the filter before an acquisition timing of the output by the acquisition means after a temperature of the filter has become not higher than the temperature, and
the calculation means calculates an amount of particulate matter in the exhaust gas per unit time and per unit volume based on the output acquired by the acquisition means, the predetermined time, and the integrated value.
A seventh aspect of the present invention is the PM amount sensing device for exhaust gas according to the fifth aspect or the sixth aspect, further comprising
an oxygen concentration sensor element disposed in an upstream of the filter in the exhaust path, and capable of changing its output according to an oxygen concentration of exhaust gas that flows into the filter, wherein
the calculation means calculates an amount of particulate matter in the exhaust gas based on a difference between an output of the oxygen concentration sensor element of the upstream side of the filter and an output of the oxygen concentration sensor element of the downstream side of the filter.
An eighth aspect of the present invention is the PM amount sensing device for exhaust gas according to the seventh aspect, wherein
the oxygen concentration sensor element of the downstream side of the filter and the oxygen concentration sensor element of the upstream side of the filter are air-fuel ratio sensor elements.
A ninth aspect of the present invention is the PM amount sensing device for exhaust gas according to the eighth aspect, further comprising
calibration means for calibrating an output deviation between the air-fuel ratio sensor of the downstream side of the filter and the air-fuel ratio sensor of the upstream side of the filter.
To achieve the above-mentioned purpose, a tenth aspect of the present invention is a PM amount sensing device for exhaust gas, comprising:
a filter provided in an exhaust path of an internal combustion engine and for filtering particulate matter (PM) in exhaust gas that flows through the exhaust path;
a heater attached to the filter;
temperature reduction control means for controlling the heater such that a temperature of the filter is not higher than a temperature at which particulate matter in the filter is not removed;
heating control means for controlling the heater such that a temperature of the filter becomes not lower than a temperature at which particulate matter in the filter is removed, after a predetermined period has elapsed since a temperature of the filter becomes not higher than the temperature through the control by the temperature reduction control means;
electric energy sensing means for sensing electric energy consumption consumed by the heater for removing particulate matter in the filter when the control by the heating control means is being performed;
calculation means for calculating an amount of particulate matter of the exhaust gas based on the electric energy consumption sensed by the electric energy sensing means.
An eleventh aspect of the present invention is the PM amount sensing device for exhaust gas according to the tenth aspect, wherein
the electric energy sensing means comprises:
determination means for determining whether or not particulate matter in the filter is removed after a start of the control by the heating control means;
electric energy calculation means for calculating electric energy consumption of the heater during a period from a start of the control by the heating control means until it is determined that the particulate matter in the filter is removed; and
calculation means for calculating the electric energy consumption consumed by the heater for removing particulate matter in the filter, based on the electric energy consumption calculated by the electric energy calculation means.
A twelfth aspect of the present invention is the PM amount sensing device for exhaust gas according to the eleventh aspect, comprising:
an upstream side oxygen concentration sensor disposed in an upstream of the filter in the exhaust path, and adapted to change its output according to an oxygen concentration of gas that flows into the filter; and
a downstream side oxygen concentration sensor disposed in a downstream of the filter in the exhaust path, and adapted to change its output according to an oxygen concentration of gas that flows out from the filter, wherein
the determination means determines whether or not the particulate matter in the filter is removed based on a difference between an output of the upstream side oxygen concentration sensor and an output of the downstream side oxygen concentration sensor.
To achieve the above-mentioned purpose, a thirteenth aspect of the present invention is an abnormality detection apparatus for an internal combustion engine, comprising:
an oxygen concentration sensor disposed in a downstream of a particulate filter provided in an exhaust path of the internal combustion engine, and adapted to change its output according to an oxygen concentration of gas that flows out from the particulate filter;
heating means for heating the particulate filter so as to regenerate the particulate filter; and
detection means for detecting an abnormality of the particulate filter based on an output of the oxygen concentration sensor of the downstream after the regeneration of the particulate filter.
The abnormality detection apparatus for an internal combustion engine according to the thirteenth aspect, further comprising
an oxygen concentration sensor disposed in an upstream of the particulate filter and adapted to change its output according to an oxygen concentration in exhaust gas, wherein
the detection means detects an abnormality of the particulate filter based on a difference between an output of the oxygen concentration sensor of the upstream and an output of the oxygen concentration sensor of the downstream.
The abnormality detection apparatus for an internal combustion engine according to the fourteenth aspect, wherein
the oxygen concentration sensor disposed in each of the upstream and the downstream of the particulate filter respectively is an air-fuel ratio sensor.

Advantageous Effects of Invention

According to a first aspect of the present invention, an oxygen concentration sensor element exhibits an output with lower oxygen concentration as the amount of particulates in a filter increases. Based on the output of the oxygen concentration sensor element, it is possible to detect the amount of particulates in the gas that flows into the filter. Further, since the particulates in the filter can be removed by heating with a heater, it is possible to repeatedly perform the sensing of the amount of particulates.
According to a second aspect of the present invention, an oxygen concentration sensor element is provided in each of the upstream side of filter and the downstream side of filter. The difference between the outputs of these oxygen concentration sensor elements correspond with high precision to the amount of particulates in the filter. Thus, based on the difference between the outputs of these oxygen concentration sensor elements, it is possible to sense with high precision the amount of particulates in the gas that flows into the filter.
According to a third aspect of the present invention, an air-fuel ratio sensor element is used as the oxygen concentration sensor element in the first and second aspects of the present invention. The air-fuel ratio sensor has a proven track record as the sensor for sensing the oxygen concentration of exhaust gas. By using an air-fuel ratio sensor element, it is possible to sense the amount of particulates in the exhaust gas with high reliability.
According to a fourth aspect of the present invention, the following effects can be obtained. The air-fuel ratio sensor generally operates while being heated to a predetermined activation temperature. On the other hand, when the temperature of the filter rises to not lower than a specific temperature, particulates will burn off without being accumulated in the filter. According to the fourth aspect of the present invention, it is ensured that the filter can hold particulates even while the temperature of the air-fuel ratio sensor is at the activation temperature. As a result, it is possible to sense the amount of particulates in the exhaust gas even while the air-fuel ratio sensor is at the activation temperature.
According to a fifth aspect of the present invention, after the filter is heated to a sufficiently high temperature, a heater is controlled such that the temperature of the filter is lowered to a level at which particulates can be trapped. After the heater control, particulates go on being trapped in the filter, and the output of the oxygen concentration sensor element is acquired. The greater the amount of particulates in the filter, the lower the oxygen concentration in the gas in the downstream of filter becomes, and the output of the oxygen concentration sensor element exhibits a lower oxygen concentration value. Therefore, based on the output of the oxygen concentration sensor element, it is possible to calculate the amount of particulates in the gas that flows into the filter. This allows the sensing of the amount of particulates in the exhaust gas.
According to a sixth aspect of the present invention, it is possible to calculate the amount of particulates in the exhaust gas per unit time and per unit volume.
According to a seventh aspect of the present invention, an oxygen concentration sensor element is provided in each of the upstream side of filter and the downstream side of filter. The difference between the outputs of these oxygen concentration sensor elements corresponds with high precision to the amount of particulates in the filter. Thus, based on the difference between the outputs of these oxygen concentration sensor elements, it is possible to sense with high precision the amount of particulates in the gas that flows into the filter.
According to an eighth aspect of the present invention, an air-fuel ratio sensor element is used as the oxygen concentration sensor element. The air-fuel ratio sensor has a proven track record as the sensor for sensing the oxygen concentration of exhaust gas. Thus, by using an air-fuel ratio sensor element, it is possible to sense the amount of particulates in the exhaust gas with high reliability.
According to a ninth aspect of the present invention, the output discrepancy among a plurality of air-fuel ratio sensors can be calibrated. This makes it possible to perform the sensing of the amount of particulates with a higher precision.
According to a tenth aspect of the present invention, it is possible to sense the amount of particulates. The greater the amount of particulates in the exhaust gas, the greater the amount of particulates to be trapped in the filter per unit time becomes. The greater the amount of particulates in the filter, the greater the electric energy consumption of heater needed to remove the particulates in the filter becomes. Therefore, it is possible to calculate the amount of particulates in the gas that flows into the filter based on the electric energy consumption of heater.
According to an eleventh aspect of the present invention, it is possible to accurately calculate the electric energy consumption that has been consumed at the heater until the particulates in the filter has been removed.
According to a twelfth aspect of the present invention, it is possible to determine with high precision whether or not the particulates in the filter are removed.
According to a thirteenth aspect of the present invention, an oxygen concentration sensor is provided in the downstream of a particulate filter. If the particulate filter is in a condition to be able to normally trap particulates, the particulates will go on accumulating in the filter so that the effect of the accumulation of particulates should manifest itself in the output of the oxygen concentration sensor. Therefore, based on the output of the oxygen concentration sensor, it is possible to detect abnormality of the particulate filter.
According to a fourteenth aspect of the present invention, an oxygen concentration sensor element is provided in each of the upstream and downstream of a particulate filter. The difference between the outputs of these oxygen concentration sensor elements corresponds with high precision to the amount of particulates in the particulate filter. Based on the difference between the outputs of these oxygen concentration sensor elements, it is possible to detect abnormality of the particulate filter with high reliability.
According to a fifteenth aspect of the present invention, an air-fuel ratio sensor is used as the oxygen concentration sensor in the fourteenth aspect of the present invention. The air-fuel ratio sensor has a proven track record as the sensor for sensing the oxygen concentration of exhaust gas. By using the air-fuel ratio sensor, it is possible to detect the abnormality of particulate filter with high reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram to show the configuration of a PM sensor and PM amount sensing device for exhaust gas according to Embodiment 1 of the present invention.

FIG. 2 is a diagram to show the view of the configuration of FIG. 1 seen from the direction of arrow A.

FIG. 3 is a time chart to illustrate the operation of sensing the amount of PM relating to Embodiment 1.

FIG. 4 is a flowchart of a routine performed by ECU 50 in Embodiment 1.

FIG. 5 is a diagram to show an example of the map of the correlation line between the value of ΔI_Land the amount of particulates (the amount of PM).

FIG. 6 is a flowchart of a routine performed by ECU 50 in Embodiment 2 according to the present invention.

FIG. 7 is a diagram to show the configuration of an abnormality detection apparatus of an internal combustion engine relating to Embodiment 3 of the present invention.

FIG. 8 is a flowchart of a routine performed by ECU 50 in Embodiment 3 according to the present invention.

REFERENCE SIGNS LIST

2 an internal combustion engine
10 an exhaust pipe
20 a partition
22, 24 an air-fuel ratio sensor (A/F sensor)
30 a filter
34 a heater control part
50 ECU (Electronic Control Unit)
130 DPF

DESCRIPTION OF EMBODIMENTS

Embodiment

1

Configuration of Embodiment 1

FIG. 1 is a diagram to show the configuration of a PM sensor and PM amount sensing device for exhaust gas according to Embodiment 1 of the present invention. FIG. 2 is a diagram to show the view of the configuration of FIG. 1 seen from the direction of arrow A. The PM sensor and the PM amount sensing device for exhaust gas according to Embodiment 1 are suitable for internal combustion engines of vehicles.
The PM sensor and the PM amount sensing device according to Embodiment 1 are mounted on an exhaust pipe 10 of an internal combustion engine 2. There is no limitation on the number and type of cylinders of the internal combustion engine 2. It is noted that the internal combustion engine 2 of FIG. 1 is schematically shown for the sake of convenience. In the exhaust pipe 10, installed are an air-fuel ratio sensor 22, a filter 30, and an air-fuel ratio sensor 24 in sequence in the direction of the flow of exhaust gas. In the following description below, for the sake of simplicity, the air-fuel ratio sensor is also referred to as “A/F sensor.” In Embodiment 1, a partition 20 shown in FIG. 1 is provided. The partition 20 opens into the left side on the page and the right side on the page of FIG. 1. Exhaust gas flows from the left side on the page of FIG. 1 to the right side on the page of FIG. 1 through the inside of the partition 20.
The filter 30 is a compact filter for trapping fine particles. The filter 30 is a small-sized version of the so-called diesel particulate filter (DPF). Hereinafter, particulate matter (PM) is also referred to simply as “particulates” or “PM”.
A part of the exhaust gas flowing in the exhaust pipe 10 of the internal combustion engine 2 flows into the filter 30. The filter 30 can filter particulates in the exhaust gas that flows thereinto. According to this, the particulates go on accumulating within the filter 30. As a result, the filter 30 can capture and collect (that is, trap) particulates.
The filter 30 can be formed by imitating the material and specific configuration of a DPF, and making its outer shape smaller than that of the DPF. The detailed structure of the filter 30 needs not necessarily be the same as or analogous to the DPF. As shown in FIG. 2, the outer-shape dimension of the filter 30 is smaller compared to the inner diameter of the exhaust pipe 10. Therefore, a portion of the exhaust gas flows into the filter 30, and the remaining gas goes on flowing to the downstream of the exhaust pipe 10 without flowing into the filter 30.
A/ F sensors 22 and 24 are A/F sensors of limiting current type. The A/F sensor of limiting current type exhibits a different limiting current value according to the oxygen concentration of the atmosphere, in other words, the oxygen concentration of the gas to be detected. The limiting current value proportionally varies according to the oxygen concentration. Therefore, the A/F sensor 22 changes its output according to the oxygen concentration of the exhaust gas in the upstream of the filter 30. Moreover, the A/F sensor 24 changes its output according to the oxygen concentration of the exhaust gas in the downstream of the filter 30 as well.
The A/ F sensors 22 and 24 each includes an outer electrode that is exposed to the gas to be detected, that is, the exhaust gas, an inner electrode which is exposed to the atmosphere, and an oxygen-ion conducting electrolyte interposed between the outer electrode and the inner electrode. The oxygen-ion conducting electrolyte favorably utilizes, for example, ZrO₂which has a high reliability. Since there is not particular limitation on the specific configurations of the A/ F sensors 22 and 24, further description thereof will be omitted.
The A/ F sensors 22 and 24 are heated to a predetermined activation temperature by a built-in heater, and thereafter perform the sensing of air-fuel ratio at the activation temperature. As shown in FIG. 1, the filter 30 and the A/ F sensor 22 or 24 are spaced apart by a predetermined distance. The distance between the filter 30 and the A/ F sensor 22 or 24 is large enough such that particulates can be present without being burnt within the filter 30 even when the A/ F sensors 22 and 24 are at the activation temperature.
The filter 30 includes a heater 32 which is a compact heater. The heater 32 connects to a heater control part 34. The heater 32 can keep the inside of the filter 30 at a high temperature so that particulates within the filter 30 can be removed. This makes it possible to reduce the amount of particulates in the filter 30 to be zero, thereby performing the regeneration of the filter 30 (regeneration of trapping capability).
In Embodiment 1, an ECU (Electronic Control Unit) 50 connects to the A/ F sensors 22 and 24, and the heater control part 34. The ECU 50 can acquire the outputs of the A/ F sensors 22 and 24, respectively. Hereinafter, for the sake of convenience, the limiting current value of the A/F sensor 22 is also referred to as an output current value I_L1, or an output I_L1; and the limiting current value of the A/F sensor 24 is referred to as an output current value I_L2, or an output I_L2. Moreover, in Embodiment 1, the ECU 50 prestores the arithmetic processing to calculate the difference between the output I_L1and the output I_L2. Hereinafter, the difference between the output I_L1and the output I_L2is also referred to as ΔI_L.
Moreover, the ECU 50 can provide the heater control part 34 with a control signal to perform on-off control of the heater 32 and regulation of its heat generation rate.
It is noted that in Embodiment 1, although not illustrated, the ECU 50 also connects to a sensor (for example, an intake pressure sensor or an air flow meter) for measuring the amount of intake air of the internal combustion engine 2, which is located in the upstream of the exhaust pipe 10. The ECU 50 can measure an intake air amount Ga of the internal combustion engine 2 based on the output of the above described sensor. In Embodiment 1, the ECU 50 stores the routine to calculate an exhaust gas amount Gexh based on the intake air amount Ga.

[Operation of Embodiment 1]

(PM Detection Principle Relating to Embodiment 1)

Having continued diligent research, the present inventors came up with the idea of a method for sensing the amount of particulates based a novel detection principle which has been unknown. That is, when particulates are filtered by a compact filter like the filter 30, the diffusion distance of the gas (oxygen: O₂) that passes through inside the compact filter varies.
The greater the amount of particulates in the filter, the longer the diffusion distance of the gas that passes through the compact filter becomes. The amount of O₂that can pass through the compact filter decreases as the amount of particulates in the filter increases; and as a result of that, the oxygen concentration in the downstream of the compact filter goes on declining. Therefore, it is possible to sense the amount of particulates in the gas that flows into the compact filter based on the oxygen concentration in the downstream of the compact filter.
In the above described series of phenomena, the compact filter plays the same role as that of a diffusion-controlled layer in a limiting current type A/F sensor. When the limiting current type A/F sensor is disposed in the downstream of the compact filter, the diffusion distance of oxygen in a layer which is the total of the compact filter and the diffusion-controlled layer of the limiting current type A/F sensor, increases as the amount of particulates in the filter increases. As a result of that, as the amount of particulates within the filter increases, the limiting current value of the limiting current type A/F sensor in the downstream goes on declining.
When a limiting current type A/F sensor is disposed respectively in the upstream and the downstream of the compact filter, as the amount of particulates in the filter increases, the difference between the outputs of the limiting current type A/F sensors of the upstream and the downstream increases. Therefore, it is possible to sense the amount of particulates in the gas that flows into the compact filter based on the difference between the outputs of the limiting current type A/F sensors of the upstream and the downstream.

(Specific Operation of Embodiment 1)

When exhaust gas having a certain air-fuel ratio and a certain amount of particulates flows into the filter 30, the A/F sensor 22 exhibits a specific output corresponding to the air-fuel ratio. On the other hand, the output of the A/F sensor 24 varies according to the amount of particulates in the filter 30 as described above. As a result of the exhaust gas continually flowing into the filter 30, the amount of particulates in the filter 30 increases. As the amount of particulates in the filter 30 increases, the oxygen concentration of the atmosphere of the A/F sensor 24 declines, and thereby I_L2declines. As a result of this, since the output I_L2goes on declining while the output I_L1stays constant, ΔI_Lincreases.
Under the condition of the same time period and the same flow rate of exhaust gas, the greater the amount of particulates contained in the exhaust gas, the further ΔI_Lincreases. Therefore, based on ΔI_L, it is possible to calculate the amount of particulates of the exhaust gas that currently flows into the filter 30. According to this, the amount of particulates generated in the internal combustion engine 2 can be sensed.
The method for sensing the amount of PM of Embodiment 1 will be described more specifically using FIG. 3. FIG. 3 is a time chart to illustrate the operation of sensing the amount of PM relating to Embodiment 1. In the operation of sensing the amount of PM of Embodiment 1, three steps of A, B, and C are repeatedly performed. In Embodiment 1, it is supposed that the A/ F sensors 22 and 24 are kept constant at the activation temperature.
In step A, first, a control signal is sent to the heater control part 34 from the ECU 50 so that the heating of the heater 32 is performed. The heating of the heater 32 will result in that the particulates in the filter 30 is removed (burnt) and the particulates in the filter temporarily becomes zero. Moreover, in Embodiment 1, in order to eliminate the discrepancy of output (output deviation) between the A/F sensor 22 and the A/F sensor 24, a zero-point correction of output is also performed in step A. This zero-point correction of output allows that ΔI_Lindicates with high precision a value corresponding to the amount of particulates in the filter 30.
In step B, the heater 32 is turned off. This will cause the temperature of the filter 30 to be lowered so that particulates start to be accumulated in the filter 30. In step B, such a state is maintained turning into a standby state until a predetermined time period has elapsed.
In step C, upon elapse of the predetermined time period from step B, the ECU 50 acquires the output I_L1and the output I_L2to calculate ΔI_L. Based on the above described predetermined time period from step B to step C (that is, the period for trapping particulates) and the total of the exhaust gas amount Gexh that has passed during the time period, the amount of particulates per unit time and unit gas amount is calculated.
After step C, step A is performed in succession. Thereafter, by repeatedly performing steps A, B, and C, it is possible to continuously sense the amount of particulates. According to Embodiment 1, it is possible to continuously perform a quantitative sensing of particulates of exhaust gas for every predetermined time period (predetermined cycle) during the operation of the internal combustion engine 2.
As described so far, according to Embodiment 1, it is possible to sense the amount of particulates of the exhaust gas that flows into the filter 30 based on the change amount of the output (the decline amount of the output) of A/F sensor 24, that is ΔI_L. Moreover, according to Embodiment 1, an A/F sensor may be provided in each of the upstream side of the filter 30 and the downstream side of the filter 30. By measuring the difference ΔI_Lbetween the A/ F sensors 22 and 24, it is possible to sense with high precision the increase in the amount of particulates in the filter 30. As a result of that, it is possible to sense with high precision the amount of particulates in the gas that flows into the filter.
Moreover, according to Embodiment 1, since the particulates of the filter 30 can be heated and thereby removed by the heater 32, it is possible to repeat the sensing of the amount of particulates. The filter 30 is compact, and the electric energy consumption of the heater 32 will be small even if the heating for removing particles is repeated. Thus, the effect on the fuel economy can be suppressed to be low.
Moreover, according to Embodiment 1, it is possible to sense the amount of particulates of exhaust gas by utilizing the A/ F sensors 22 and 24. The air-fuel ratio sensor has a proven track record as the sensor for sensing the oxygen concentration of exhaust gas. By using an air-fuel ratio sensor, it is possible to sense the amount of particulates in the exhaust gas with a high reliability.
Moreover, an air-fuel ratio sensor generally operates while being heated to a predetermined activation temperature. If the temperature of the filter 30 rises to not lower than a specific temperature (a burning temperature of particulates), particulates will burn off without being accumulated in the filter 30. In this connection, according to Embodiment 1, the A/ F sensors 22 and 24 and the filter 30 are spaced apart. Therefore, it is ensured that the filter 30 can hold particulates even while the temperature of the A/ F sensors 22 and 24 are at the activation temperature. As a result, it is possible to sense the amount of particulates in the exhaust gas even while the A/ F sensors 22 and 24 are at the activation temperature. Further, according to Embodiment 1, the temperature of the A/ F sensors 22 and 24 is kept constant at the activation temperature, and the temperature dependency of the output of the A/ F sensors 22 and 24 is small. Therefore, Embodiment 1 does not need the temperature correction of output and a temperature sensor for temperature correction, and therefore is advantageous.

[Specific Processing of Embodiment 1]

Hereinafter, specific processing performed by the PM amount sensing device for exhaust gas according to Embodiment 1 will be described by using FIG. 4. FIG. 4 is a flowchart of a routine performed by ECU 50 in Embodiment 1. The routine of FIG. 4 are executed during the startup of the internal combustion engine 2. FIG. 5 is a diagram to show an example of the map of the correlation line between the value of ΔI_Land the amount of particulates (the amount of PM). Correlation lines respectively for air- fuel ratios 20 and 25 are shown in FIG. 5. In Embodiment 1, the correlation map for air-fuel ratio=20 shown in FIG. 5 is prestored in the ECU 50.
In the routine shown in FIG. 4, first, A/F sensor heating and heater control are performed (step S100). In this step, after the startup of the internal combustion engine 2, the heater incorporated in each of the A/ F sensors 22 and 24 is controlled for heating until the A/ F sensors 22 and 24 become activated. At the same time, the heater 32 is also controlled so that the filter 30 is heated to a burning temperature of particulate.
Next, after the determination of sensor activation and PM burning, a zero-point correction of output for the A/F sensors is performed (step S102). In this step S102, first, it is determined whether or not the A/ F sensors 22 and 24 are activated. The determination of sensor activation can be performed by, for example, whether or not the error of the output of the A/ F sensor 22 or 24 is within a predetermined range. Moreover, in this step S102, the determination of PM burning is also performed. The determination of PM burning is performed to determine whether or not particulates adhered to the filter 30 have burnt off completely. In Embodiment 1, it is determined that particulates have completely burnt off if the heating of the filter 30 by the heater 32 is continued for a predetermined time period.
In step S102, a zero-point correction of output for the A/F sensors is performed as well. The zero-point correction of output for the A/F sensor is performed to eliminate the discrepancy of output (output deviation) between the A/F sensor 22 and the A/F sensor 24. This zero-point correction of output, for example, can be performed as follows. First, a power factor k to be multiplied against the output current of the A/F sensor 24 is derived such that the output of the A/F sensor 22 agrees with the output of the A/F sensor 24. This factor k is multiplied against the output current of the A/F sensor 24. This allows the difference between outputs to be cancelled every time the processing of step S102 is performed thus realizing a zero-point correction of output.
Next, the heater 32 is turned off (step S104). When the heater 32 is turned off, the temperature of the filter 30 is lowered and, after a while, the filter 30 is sufficiently cooled to a temperature at which particulates can be accumulated within the filter 30. Thereafter, particulates go on accumulating in the filter 30.
After the heater is turned off, the determination processing of filter temperature is executed for ECU 50 to determine whether or not the temperature of the filter 30 is lowered to a level where particulates can be accumulated. In this filter temperature determination, for example, the determination on whether or not the temperature of the heater 32 is sufficiently lowered may be made based on the comparison between the resistance value of the heater 32 and a predetermined value. It may be determined that the temperature of the filter 30 is sufficiently low when the heater 32 is at a sufficiently low temperature. Alternatively, it may be determined that the temperature of the filter 30 is sufficiently lowered when ΔI_Lincreases to a predetermined criterion. When a fulfillment of the condition of the determination processing of
24 and the storing of the exhaust gas amount may be performed after elapse of the predetermined time period T₀. When the engine operating region in which sensing of the amount of PM is desired to be performed is determined, or when sensing of the amount of PM is desired to be performed while the amount of generated particulates is considerably large in the view point of sensing accuracy, the operating conditions when the sensing of the amount of PM is performed may be defined in advance.
After step S108, the processing of ΔI_Lcalculation is performed (step S110). In this step, first, difference between the output values that are stored in step S108 is calculated. Next, in Embodiment 1, the difference obtained by that calculation is converted into a reference current value according to the air-fuel ratio and the exhaust gas amount Gexh. In Embodiment 1, the reference current value is supposed to be the output current value of the A/ F sensor 22 or 24 when the air-fuel ratio=20, and exhaust gas amount=10 g/s. The reference is unified by this conversion and a final ΔI_Lis calculated.
Next, the processing to calculate the amount of PM from a correlation line is performed (step S112). In step S112, a map in which the correlation line for air-fuel ratio=20 is defined as shown in FIG. 5 is referred to calculate the amount of PM according to ΔI_Lafter conversion. Specifically, in this processing, as ΔI_Lincreases, the calculated amount of PM increases as shown in the map of FIG. 5.
The following effects are achieved by the above described steps S110 and S112. For example, as shown in FIG. 5, the difference ΔI_L2that is obtained when air-fuel ratio=25-coincides with the difference ΔI_L2when air-fuel ratio=20, by being converted into a reference current value. The relationship between the amount of PM and ΔI_Lvaries according to the air-fuel ratio of exhaust gas. As shown in FIG. 5, when ΔI_L1is obtained when air-fuel ratio is 20, the amount of PM corresponding to this ΔI_L1is determined. On the other hand, if ΔI_L2is obtained when air-fuel ratio is 25, it will be the same value, as the amount of PM, as ΔI_L2when air-fuel ratio=20, even if ΔI_L2is larger than ΔI_L2. In Embodiment 1, the difference between the outputs of the A/ F sensors 22 and 24 that are obtained at different air-fuel ratios of exhaust gas is converted into a value according to air-fuel ratio=20 through the conversion processing of step S110. Besides this conversion being performed, a map is referred to in which the correlation line for air-fuel ratio=20 is defined. This makes it possible to accurately sense the amount of PM based on the outputs of the A/ F sensors 22 and 24 even under the situation where the air-fuel ratio varies every moment.
Next, the amount of PM according to the amount of exhaust gas is calculated (step S114). In this step, the amount of particulates per unit time and per unit gas amount are calculated based on the integrated exhaust gas amount Gexh_itg stored in step S108 and a predetermined time period T_o. This makes it possible to perform quantitative evaluation of particulates in the exhaust gas.
Next, the heater 32 is heated again and particulates in the filter 30 are removed (step S116). Thereafter, the process returns to step S102, and the processing after step S102 are repeatedly executed.
According to the above described processing, it is possible to sense the amount of particulates in the exhaust gas.
It is noted that the map in which the relation between ΔI_Land the amount of PM to be stored in the ECU 50 may be a so-called multi-dimensional map in which correlation lines are defined for multiple air-fuel ratios including 20, 25 and others. By utilizing this, the amount of PM may be calculated by directly referring to the correlation lines for each air-fuel ratio without performing the conversion into the reference current value of step S110. Moreover, in Embodiment 1, the ECU 50 calculates the exhaust gas amount Gexh based on the intake air amount Ga. Therefore, it is possible to use an integrated value of the intake air amount Ga in place of the integrated exhaust gas amount Gexh_itg.
It is noted that in Embodiment 1 described above, the filter 30 corresponds to the “filter” in the first invention, the heater 32 corresponds to the “heater” in the first invention, and the A/F sensor 24 corresponds to the “oxygen concentration sensor element” in the first invention, respectively. Moreover, in Embodiment 1, the A/F sensor 22 corresponds to the “oxygen concentration sensor element” in the second invention.
It is noted that in Embodiment 1 described above, the filter 30 corresponds to the “filter” in the fifth invention; the air-fuel ratio sensor 24 to the “oxygen concentration sensor element” in the fifth invention; and the heater 32 to the “heater” in the fifth invention, respectively. Moreover, in Embodiment 1, the “heating control means” in the fifth invention is implemented by the ECU 50 executing the processing of step S100 or step S116; the “temperature reduction control means” in the fifth invention by the ECU 50 executing the processing of step S104; the “acquisition means” of the fifth invention by the ECU 50 executing the processing of step S108; and the “calculation means” of the fifth invention by the ECU 50 executing the processing of steps S110 to S114, respectively in the routine of FIG. 4.
Moreover, in Embodiment 1, the predetermined time period T₀corresponds to the “predetermined time period” in the sixth invention, and the integrated exhaust gas amount Gexh_itg to the “integrated value” in the sixth invention, respectively.
Furthermore, in Embodiment 1, the “calibration means” in the ninth invention is implemented by the ECU 50 executing the processing of step S102 in the routine of FIG. 4.

[Variant of Embodiment 1]

[First Variant]

In Embodiment 1, the A/ F sensors 22 and 24 utilize an air-fuel ratio sensor of limiting current type. The present invention, however, is not limited to this. As described above, as the amount of particulates in the filter 30 increases, the amount of O₂that can pass through a compact filter decreases, and consequently the oxygen concentration in the downstream of the filter 30 goes on declining. Embodiment 1 utilizes this phenomenon to sense the amount of particulates in the gas that flows into the filter 30 based on the oxygen concentration in the downstream of the filter 30. In this connection, any air-fuel ratio sensor of type other than the limiting current type, for example, an air-fuel ratio sensor of two-cell type may be used in place of the A/ F sensors 22 and 24. Moreover, any oxygen concentration sensor other than the air-fuel ratio sensor, which can linearly measure the oxygen concentration of gas, may be used in place of the A/ F sensors 22 and 24.

(Second Variant)

In Embodiment 1, one A/F sensor is provided for each of the upstream and the downstream of the filter 30. The present invention, however, is not limited to this. As described above, as the amount of particulates in the filter 30 increases, the amount of O₂that can pass through a compact filter decreases, and consequently the oxygen concentration in the downstream of the filter 30 goes on declining. Therefore, an A/F sensor may be provided only in the downstream of the filter 30 so that the decline amount of the output (hereafter, ΔI_Ld) of this A/F sensor may be used in place of ΔI_L. However, when an A/F sensor or an oxygen concentration sensor is provided only in the downstream of the filter, it is not possible to sense the oxygen concentration of exhaust gas in the upstream of the filter 30. In this case, for example, the difference between the air-fuel ratio or the oxygen concentration, which is calculated based on the operating condition of the internal combustion engine 2, and the output of the A/F sensor or the oxygen concentration sensor in the downstream of the filter may be utilized as ΔI_L.

(Third Variant)

In Embodiment 1, the “PM sensor” relating to the first invention is configured by combining the A/ F sensors 22 and 24, the filter 30, and the heater 32, respectively as discrete parts. The present invention is, however, not limited to this configuration. A single PM sensor may be fabricated in which the functions of the element parts of the A/ F sensors 22 and 24, the filter 30 and the heater 32 are integrated (unified).
Specifically, a filter for filtering PM is provided in a case for the PM sensor which includes an inlet port of exhaust gas and an outlet port of exhaust gas. Further, an air-fuel ratio sensor element part or an oxygen concentration sensor element part is provided respectively in the upstream and the downstream of the filter. A heater for heating the filter is also incorporated. As described so far, there is provided a PM sensor which includes an inlet port and an outlet port of exhaust gas, and incorporates a filter, an oxygen concentration sensor element part, and a heater. When this PM sensor is disposed in the exhaust path, part of the exhaust gas is drawn out via the outlet port to flow into the inside of the case for PM sensor. The exhaust gas that has flowed from the inlet port passes through the filter, and thereafter flows out from the outlet port into the exhaust path again. In this configuration, it is possible to sense the amount of particulates in the exhaust gas by treating the difference in the outputs of the oxygen concentration sensors of the upstream and downstream of the filter, in the same manner as ΔI_Lof Embodiment 1.
According to the unified PM sensor relating to the present variant, since the effects of the flow rate of exhaust gas and the air-fuel ratio are reduced compared with the configuration of Embodiment 1, it is possible to perform the sensing of the amount of PM with high precision without being subject to these effects. When performing the above described unification, it is preferable that thermal insulation around the filter is sufficiently ensured so that the filter can hold particulates even while the temperature of the air-fuel ratio sensor element is at the activation temperature. It is noted that as described in the second variant above, an air-fuel ratio sensor element part or an oxygen concentration sensor element part may be provided only in the downstream of the filter.

(Fourth Variant)

It is noted that in Embodiment 1, the following variation of the calculation process is possible as well. First, the ECU 50 stores a map (first map) between the value of I_L1and the value of I_L2, and the oxygen concentration. Moreover, the ECU 50 is also made to store a map (second map) of correlation lines that define the relationship between the oxygen concentration difference ΔO₂between the upstream and the downstream of the filter 30, and the amount of PM. This second map can be defined such that the larger the oxygen concentration difference ΔO₂, the larger the amount of PM becomes. After the ECU 50 acquires I_L1and I_L2in step S108, an oxygen concentration value corresponding to those values is calculated according to the above described first map. Next, based on the difference of the oxygen concentration values, the amount of PM is calculated according to the second map. Such calculation process may substitute for the processing of steps S110 and S112.

Embodiment 2

Configuration of Embodiment 2

The PM amount sensing device of Embodiment 2 has a configuration in which a circuit for measuring the electric power consumption of the heater 32 is added to the configuration of Embodiment 1. There is no limitation on the specific configuration of this circuit, and any circuit having a current sensor and a voltage sensor for measuring the current and applied voltage of the heater 32 may be used. Since, excepting this point, the hardware configurations of Embodiment 1 and Embodiment 2 are the same, the hardware configuration of Embodiment 2 will not be illustrated for simplifying the description. The PM amount sensing device of Embodiment 2 may be implemented by causing the ECU 50 to execute the routine shown in FIG. 6 in the above described configuration.
In the following description, the electric power consumption of the heater 32 will also be referred to as “P_H”. Moreover, a quantity obtained by a time integration of the electric power consumption P_Hof the heater 32, that is, the electric energy consumption of the heater 32, is also referred to as “W_H”.

[Operation of Embodiment 2]

The greater the amount of particulates in the exhaust gas, the greater the amount of particulates to be trapped in the filter 30 per unit time becomes. The greater the amount of particulates in the filter 30, the greater the electric energy consumption of the heater 32 needed to remove the particulates in the filter 30 becomes. Accordingly, in Embodiment 2, the amount of particulates in the gas that flows into the filter 30 is calculated based on the electric energy consumption of the heater 32.

[Specific Processing of Embodiment 2]

Hereinafter, specific processing performed by the PM amount sensing device for exhaust gas according to Embodiment 2 will be described by using FIG. 6. FIG. 6 is a flowchart of a routine performed by ECU 50 in Embodiment 2. In Embodiment 2, a map of the correlation lines between W_Hand the amount of PM are prestored in the ECU 50. This map can be defined such that the larger the electric energy consumption W_His, the larger the amount of PM becomes, as with the map of Embodiment 1 in FIG. 5.
In the routine of FIG. 6, first, step S100 described in Embodiment 1 is executed.
Next, the storing of I_L1, I_L2, and Gexh, and the calculation of ΔI_Lare performed (step S208). In Embodiment 2, successive storage processing to repeatedly store (sample) the outputs I_L1and I_L2of the A/ F sensors 22 and 24, respectively at a predetermined period (for example, for every 8 milliseconds) is provided in the ECU 50. Moreover, in Embodiment 2, successive storage processing to store the exhaust gas amount Gexh at the same timing with the storing of the outputs I_L1and I_L2is also provided in the ECU 50. In step S208, the ΔI_Lcalculation processing of steps S108 and S110 is repeatedly performed based on the storage values I_L1, I_L2, and Gexh of the above described successive storage processing. In Embodiment 2, the ECU 50 continually executes these processing after step S208, and ΔI_Lis successively updated to the latest value.
Next, step S104 described in Embodiment 1 is executed and the heater is turned off. Thereafter, as particulates go on accumulating in the filter 30, the value of ΔI_Lthat is successively calculated gradually increases.
Next, when ΔI_Lreaches a predetermined value, time count is started (step S213). This step allows that the time count is started at a stage where a predetermined level of particulates have accumulated in the filter 30. This makes it possible to carry out the processing thereafter under the situation where particulates are being surely trapped in the filter 30. Consequently, it is realized that estimation accuracy of the calculation of PM amount is ensured, and the electric energy consumption of the heater under the condition where particulates are not being trapped is reduced.
Next, when the time that is started to count in step S213 reaches a predetermined time period (hereinafter, referred to as “T₁”), the heater is turned ON (step S214). After the heater 32 is turned ON, electric power is supplied to the heater 32 at a predetermined amplitude P₀and a predetermined duty ratio D_H. At this time, the heater 32 is controlled so as to be able to heat the filter 30 at lease to a temperature not lower than the temperature at which particulates start to burn. Moreover, in Embodiment 2, time is counted after the heater 32 is turned ON.
After the start of the control of the heater 32 in step S214, the filter 30 is heated by the heater 32 and particulates in the filter 30 go on burning to be removed. As a result of this, the value of ΔI_Lgradually decreases.
Thereafter, the electric energy consumption until ΔI_Lbecomes zero is calculated (step S216). In Embodiment 2, first, the heater 32 is turned ON, and thereafter determination processing on whether or not ΔI_Lbecomes zero is performed. The counting of time is stopped at the timing when ΔI_L=0 is fulfilled, and a time period T_Hfrom the ON time of the heater 32 to a time when ΔI_Lbecomes zero is obtained. Next, calculation processing to calculate the electric energy consumption W_Hbased on the time period T_H, the above described P_o, and the duty ratio D_H(to be specific, for example, multiplication of T_H×P_o×D_H=W_H) is executed. The calculated electric energy consumption W_His assumed to be the electric energy consumed by the heater 32 to remove particulates in the filter 30.
Next, the amount of PM according to the amount of exhaust gas is calculated (step S218). In this step, first, the map of the correlation lines of W_Hand the amount of PM stored in the ECU 50 is referred so that the amount of PM according to W_His calculated. Thereafter, as with Embodiment 1, the amount of particulates per unit time and per unit gas amount are calculated based on the integrated exhaust gas amount Gexh_itg and the predetermined time period T_o.
Thereafter, the heater 32 is heated again so that particulates in the filter 30 are removed (step S220). Thereafter, the process returns to step S208, and the processing after step S208 are repeatedly executed.
According to the above described processing, it is possible to sense the amount of particulates in the exhaust gas.
It is noted that in Embodiment 2 described above, the filter 30 corresponds to the “filter” in the tenth invention; and the heater 32 to the “heater” in the tenth invention, respectively. Moreover, in Embodiment 2, the “temperature reduction control” in the tenth invention is implemented by the ECU 50 executing the processing of step S212; the “heating control means” in the tenth invention by the ECU 50 executing the processing of step S213 and step S214; the “electric energy sensing means” of the tenth invention by the ECU 50 executing the processing of step S216; and the “calculation means” of the tenth invention by the ECU 50 executing the processing of step S220, respectively in the routine of FIG. 6.
Moreover, in Embodiment 2, the “determination means” in the eleventh invention is implemented by the ECU 50 executing the determination processing on whether or not ΔI_Lis zero; and the “electric energy calculation means” in the eleventh invention by the ECU 50 executing the calculation processing to calculate electric energy consumption W_Hbased on the time period T_H, the above described P_o, and the duty ratio D_H, in step S216 of FIG. 6.
Moreover, although the hardware configuration is not illustrated in Embodiment 2, the A/F sensor 22 corresponds to the “upstream side oxygen concentration sensor” in the above described twelfth invention; and the A/F sensor 24 not shown corresponds to the “downstream side oxygen concentration sensor” in the twelfth invention.

[Variant of Embodiment 2]

In the specific processing of Embodiment 2, the outputs of the A/ F sensors 22 and 24 when the predetermined time period T₁elapsed are stored in step S214. The present invention, however, is not limited to this configuration. The ECU 50 may store, in place of the time period T₁, the outputs of the A/ F sensors 22 and 24 when the integrated exhaust gas amount Gexh_igt reaches a predetermined amount.
The control of the heater 32 is not limited to the duty control as in step S214. For example, electric power may be supplied to the heater 32 such that the resistance value (temperature of the heater 32) indicates a predetermined value. In this case, the electric energy consumption may be calculated such as by monitoring electric power consumption of the heater 32.
In Embodiment 2, variants include one as shown below. In this variant, when the predetermined time period has elapsed (or the exhaust gas integrated value has reached a predetermined amount) after the heater-off processing in step S212, the processing after the heater-on processing in step S214 is executed. That is, in the present variant, the comparison of ΔI_Lwith a predetermined value in step S213 is eliminated.
Moreover, variants described in Embodiment 1 may be combined with Embodiment 2.

Embodiment 3

Configuration of Embodiment 3

FIG. 7 is a diagram to show the configuration of an abnormality detection apparatus of an internal combustion engine relating to Embodiment 3 of the present invention. The abnormality detection apparatus of Embodiment 3 can detect abnormality of a diesel particulate filter (DPF) 130 provided in the exhaust pipe 10. This abnormality detection apparatus can be used for OBD (On-board Diagnosis) while being mounted on a vehicle.
In Embodiment 3, it is supposed that the internal combustion engine 2 is a diesel engine, and a heating mechanism (not shown) for regenerating the DPF 130 is provided. The ECU 50 can control the heating mechanism to regenerate the DPF 130.
There are already various known configurations regarding the heating mechanism for the regeneration of DPF. Therefore, although detailed description will not be made, the DPF 130 may be heated by, for example, so-called post injection. To be specific, an exhaust fuel-addition valve may be provided in the exhaust path of the internal combustion engine 2. The exhaust fuel-addition valve is provided to add fuel to the exhaust gas flowing in the exhaust path. By performing fuel addition with the exhaust fuel-addition valve at an appropriate timing, it is possible to regenerate the DPF 130. Moreover, so-called post injection may be performed to perform fuel addition. Moreover, a heater may be attached to the DPF 130 to heat the DPF 130 by this heater.
As shown in FIG. 7, A/ F sensors 22 and 24 are provided in the upstream and the downstream of the DPF 130 as with the filter 30 of Embodiment 1. In the DPF 130 as well, as in the filter 30, as the amount of particulates increases, ΔI_Lincreases. If the DPF 130 is in a condition to be able to normally trap particulates, the particulates will go on to accumulate in the DPF 130, and the effect of the accumulation of particulates should manifest itself in ΔI_L. Therefore, it is possible to detect abnormality of the DPF 130 based on ΔI_L.

[Specific Processing of Embodiment 3]

FIG. 8 is a flowchart of the routine to be executed by the ECU 50 in Embodiment 3. It is supposed that the routine of FIG. 8 is executed during the startup of the internal combustion engine 2. In the following description, description will be omitted or simplified as appropriate on overlapping points in the contents with those of Embodiments 1 and 2.
In the routine of FIG. 8, first, heating to activate the A/F sensor is performed as with step S100 of Embodiment 1 (step S300).
Then, DPF regeneration control is performed (step S302). In this step, the ECU 50 controls the heating mechanism, which has been already described, so that particulates in the DPF 130 are removed.
Next, steps S102, S106, S108, and S110 are executed as in Embodiment 1. Thereby, the determination processing of A/F sensor activation, the determination processing of PM burning in DPF 130, the zero-point correction processing of the output of the A/F sensor, the calculation processing of the integrated exhaust gas amount Gexh_itg, and the calculation processing of ΔI_Lare successively executed.
Next, the amount of PM is calculated (step S304). In this step, based on ΔI_L, the amount of PM is calculated according to correlation lines as with the processing of step S112 of Embodiment 1. In Embodiment 3 as well, a map of correlation lines as shown in FIG. 5 is created and stored in the ECU 50.
Next, it is determined whether or not the amount of PM is not more than a predetermined value (step S306). As described so far, if the DPF 130 is in a condition to be able to normally trap particulates, particulates should go on accumulating in the DPF 130. When, contrary to such an expectation, the amount of PM in the DPF 130 indicates a value not more than the predetermined value, it is considered that an abnormality of some kind has occurred in the DPF 130. Therefore, the determination on whether or not the amount of PM is not more than the predetermined value is performed in Embodiment 3. When this condition is negated, it is judged that the DPF 130 is normally trapping particulates, and the routine of this round ends.
When the condition of step S306 holds, it is determined that there is an abnormality in DPF 130 (step S308). When the abnormality detection apparatus of Embodiment 3 is being used for OBD, alerting the driver by, for example, lighting an alarm lamp is performed.
According to the above described processing, it is possible to perform the detection of abnormality in a particulate filter.
It is noted that, in Embodiment 3, after the amount of PM is calculated from ΔI_L, determination based on the comparison between the amount of PM and the predetermined value is performed. The present invention, however, is not limited to this arrangement. The comparison determination may be made by comparing ΔI_Lwith a predetermined value without performing the conversion to the amount of PM.
It is noted that in Embodiment 3 described above, the DPF 130 corresponds to the “particulate filter” in the thirteenth invention, and the A/F sensor 24 to the “oxygen concentration sensor” in the thirteenth invention, respectively. Moreover, the “heating means” in the thirteenth invention is implemented by the ECU 50 executing the processing of step S302 in the routine of FIG. 8, and the “detection means” in the thirteenth invention by the ECU 50 executing the processing of steps S110, S304, S306, and S308 in the routine of FIG. 8, respectively.
Moreover, in Embodiment 3 described above, the A/F sensor 22 corresponds to the “oxygen concentration sensor” in the fourteenth invention.

Claims

1. A PM sensor, comprising:

an inlet port through which a portion of gas that is drawn from an exhaust path of an internal combustion engine is allowed to flow in;

a filter for filtering particulate matter (PM) in the gas that has flowed in through the inlet port;

a heater attached to the filter and capable of changing the temperature of the filter;

an outlet port through which the gas that has passed through the filter is allowed to flow out to the exhaust path; and

an oxygen concentration sensor element disposed in the outlet port side and including a heater, wherein the oxygen concentration sensor is heated to a predetermined temperature by the heater upon being activated and is adapted to change its output according to an oxygen concentration of gas that has passed through the filter, and wherein the oxygen concentration sensor is disposed being spaced apart from the filter such that the filter has a level of temperature at which particulate matter in the filter is not removed when temperature of the oxygen concentration sensor itself is at the predetermined temperature.

2. The PM sensor according to claim 1, further comprising

an oxygen concentration sensor element disposed between the inlet port and the filter and adapted to change its output according to an oxygen concentration of gas that has flowed in through the inlet port.

3. The PM sensor according to claim 2, wherein

the oxygen concentration sensor element of the outlet port side and the oxygen concentration sensor element of the inlet port side are air-fuel ratio sensor elements.

4. (canceled)

5. A PM amount sensing device for exhaust gas, comprising:

a filter provided in an exhaust path of an internal combustion engine and for filtering particulate matter (PM) in exhaust gas that flows through the exhaust path;

an oxygen concentration sensor element disposed in a downstream of the filter in the exhaust path, and adapted to change its output according to an oxygen concentration of gas that has passed through the filter;

a heater attached to the filter;

heating control means for controlling the heater such that the filter is heated until particulate matter in the filter is removed;

temperature reduction control means for controlling the heater such that a temperature of the filter is not higher than a temperature at which particulate matter in the filter is not removed, after the control of the heating control means;

acquisition means for acquiring an output of the oxygen concentration sensor element when a predetermined time period has elapsed after a temperature of the filter becomes not higher than the temperature;

means for calculating an integrated value of an amount of exhaust gas that flows into the filter before an acquisition timing of the output by the acquisition means; and

calculation means for calculating an amount of particulate matter in the exhaust gas per unit time and per unit volume based on the output acquired by the acquisition means, the predetermined time period, the and the integrated value.

6. (canceled)

7. The PM amount sensing device for exhaust gas according to claim 5, further comprising

an oxygen concentration sensor element disposed in an upstream of the filter in the exhaust path, and capable of changing its output according to an oxygen concentration of exhaust gas that flows into the filter, wherein

the calculation means calculates an amount of particulate matter in the exhaust gas based on a difference between an output of the oxygen concentration sensor element of the upstream side of the filter and an output of the oxygen concentration sensor element of the downstream side of the filter.

8. The PM amount sensing device for exhaust gas according to claim 7, wherein

the oxygen concentration sensor element of the downstream side of the filter and the oxygen concentration sensor element of the upstream side of the filter are air-fuel ratio sensor elements.

9. The PM amount sensing device for exhaust gas according to claim 8, further comprising

calibration means for calibrating an output deviation between the air-fuel ratio sensor of the downstream side of the filter and the air-fuel ratio sensor of the upstream side of the filter.

10. A PM amount sensing device for exhaust gas, comprising:

a heater attached to the filter;

an upstream side oxygen concentration sensor disposed in an upstream of the filter in the exhaust path, and adapted to change its output according to an oxygen concentration of gas that flows into the filter;

a downstream side oxygen concentration sensor disposed in a downstream of the filter in the exhaust path, and adapted to change its output according to an oxygen concentration of gas that flows out from the filter;

temperature reduction control means for controlling the heater such that a temperature of the filter is not higher than a temperature at which particulate matter in the filter is not removed;

heating control means for controlling the heater such that a temperature of the filter becomes not lower than a temperature at which particulate matter in the filter is removed, after a predetermined period has elapsed since a temperature of the filter becomes not higher than the temperature through the control by the temperature reduction control means;

electric energy sensing means including:

determination means for determining whether or not particulate matter in the filter is removed based on a difference between an output of the upstream side oxygen concentration sensor and an output of the downstream side oxygen concentration sensor after a start of the control by the heating control means,

electric energy calculation means for calculating electric energy consumption of the heater during a period from a start of the control by the heating control means until it is determined that particulate matter in the filter is removed; and

means for calculating electric energy consumption consumed by the heater for removing particulate matter in the filter based on the electric energy consumption calculated by the electric energy calculation means; and

calculation means for calculating an amount of particulate matter of the exhaust gas based on the electric energy consumption sensed by the electric energy sensing means.

11-15. (canceled)

16. A PM amount sensing device for exhaust gas, comprising:

a heater attached to the filter;

a heating control unit for controlling the heater such that the filter is heated until particulate matter in the filter is removed;

a temperature reduction control unit for controlling the heater such that a temperature of the filter is not higher than a temperature at which particulate matter in the filter is not removed, after the control of the heating control unit;

an acquisition unit for acquiring an output of the oxygen concentration sensor element when a predetermined time period has elapsed after a temperature of the filter becomes not higher than the temperature;

an unit for calculating an integrated value of an amount of exhaust gas that flows into the filter before an acquisition timing of the output by the acquisition unit; and

a calculation unit for calculating an amount of particulate matter in the exhaust gas per unit time and per unit volume based on the output acquired by the acquisition unit, the predetermined time period, the and the integrated value.

17. A PM amount sensing device for exhaust gas, comprising:

a heater attached to the filter;

a temperature reduction control unit for controlling the heater such that a temperature of the filter is not higher than a temperature at which particulate matter in the filter is not removed;

a heating control unit for controlling the heater such that a temperature of the filter becomes not lower than a temperature at which particulate matter in the filter is removed, after a predetermined period has elapsed since a temperature of the filter becomes not higher than the temperature through the control by the temperature reduction control unit;

an electric energy sensing unit including:

a determination unit for determining whether or not particulate matter in the filter is removed based on a difference between an output of the upstream side oxygen concentration sensor and an output of the downstream side oxygen concentration sensor after a start of the control by the heating control unit,

an electric energy calculation unit for calculating electric energy consumption of the heater during a period from a start of the control by the heating control unit until it is determined that particulate matter in the filter is removed; and

an unit for calculating electric energy consumption consumed by the heater for removing particulate matter in the filter based on the electric energy consumption calculated by the electric energy calculation unit; and

a calculation unit for calculating an amount of particulate matter of the exhaust gas based on the electric energy consumption sensed by the electric energy sensing unit.