JP2013253794A - Particulate matter detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particulate matter detection system capable of accurately detecting degradation or performance deterioration of a PM sensor.SOLUTION: A particulate matter detection system comprises: a sensor element (40) which is installed in an exhaust passage (6b) of an internal combustion engine (2), has insulator adhesion sections (44) with a pair of electrodes formed thereon and outputs, when the pair of electrodes are electrically conducted with more than predetermined amount of particulate matters adhered to the adhesion sections, a value according to the amount of particulate matters adhered to the adhesion sections; a detection section (46) which detects the value output by the sensor element; a heater (43) which removes the particulate matters adhered to the adhesion sections by heating the same; heater energization control sections (45 and 49) which perform conduction control of the heater; and a degradation level estimation calculation section (49) which performs estimation calculation with respect to a degradation level of the heater on the basis of the detection value of the detection section when the heater is energized.

Description

  The present invention relates to a particulate matter detection system for detecting particulate matter in exhaust gas from an internal combustion engine.

  Today, there is a demand for excellent exhaust purification performance for internal combustion engines. In particular, in a diesel engine, it is important to remove so-called exhaust particulates (particulate matter, PM) such as black smoke discharged from the engine. In order to remove PM, a diesel particulate filter (DPF: Diesel Particulate Filter) is often provided in the middle of the exhaust pipe.

  There is a PM sensor as means for detecting the amount of PM in the exhaust. For example, when a PM sensor is arranged downstream of the DPF, it can be determined whether or not the DPF is out of order using the detection value of the PM sensor. In the future, it is expected that vehicle post-processing failure detection will become more severe, and it is necessary to equip a PM sensor to detect failure of the DPF. For this purpose, the PM sensor itself must be normal, and PM sensor failure detection (determination of PM sensor rationality) is also important.

  An electrode-type PM sensor has an insulator attachment portion on which a pair of electrodes are formed. The PM sensor is provided in the exhaust passage, and is used with a voltage applied between a pair of electrodes. PM contained in the exhaust gas adheres to the adhesion portion of the PM sensor. Since PM is mainly composed of soot (that is, carbon particles) and has conductivity, a current flows between the electrodes when the PM adheres to the adhering portion more than a certain amount. The value of the current is a value according to the amount of PM adhering, that is, a value according to the amount of PM contained in the exhaust gas. Therefore, by reading the current value (resistance value between the electrodes corresponding to the current value) The amount of PM can be detected.

  If a large amount of PM accumulates on the adhesion part of the PM sensor, detection of the PM amount is hindered. Therefore, if it is considered that a large amount of PM has accumulated (adhered) on the PM sensor, the adhesion part is attached by a heater included in the PM sensor. The PM sensor is regenerated by heating (or the electrode) and burning and removing the deposited PM (see Patent Document 1).

JP 59-196453 A

  With the configuration of the prior art, the failure due to the disconnection of the heater can be easily determined because the attached matter cannot be removed at all even if the heater is energized (the energization state does not change). However, since the heater can be energized with respect to the deterioration or performance degradation of the heater, it cannot be easily determined.

  Against the background of the above problems, an object of the present invention is to provide a particulate matter detection system capable of accurately detecting deterioration or performance degradation of a PM sensor.

Means for Solving the Problems and Effects of the Invention

  A particulate matter detection system for solving the above problems is provided in an exhaust passage (6b) of an internal combustion engine (2) and has an insulator attachment portion (44) in which a pair of electrodes are formed. A sensor element (40) for outputting a value corresponding to the amount of particulate matter adhering to the adhering portion when the particulate matter adheres to the adhering portion when the particulate matter adheres to the adhering portion; A detection unit (46) that detects a value output from the sensor element, a heater (43) that heats and removes particulate matter adhering to the adhering unit, and a heater energization control unit (45, 45) that controls energization of the heater 49) and a deterioration level estimation calculation unit (49) for estimating and calculating the deterioration level of the heater based on the detection value of the detection unit when the heater is energized.

  With the above-described configuration, it is possible to detect / determine heater deterioration or performance degradation in addition to failure due to heater disconnection. Further, it is not necessary to add a new circuit or device for the detection / determination, and there is an advantage that the cost of the system does not increase.

  Further, the heater energization control unit in the particulate matter detection system of the present invention can be configured to correct the energization state of the heater according to the deterioration level of the heater.

  With the above configuration, the PM sensor can be regenerated even if the heater is deteriorated or the performance is degraded.

The figure which shows the structural example of the exhaust gas purification system of the internal combustion engine to which a particulate matter detection system is applied. The figure which shows the example of the structure of PM sensor (particulate matter detection system). The figure which shows the detail of the structure of PM sensor of FIG. The imming chart which shows the example of the output of PM sensor. The flowchart explaining a heater deterioration estimation process. The figure explaining the relationship between a heater deterioration level, an initial raise amount, and a threshold value. The figure which shows the relationship between a heater deterioration level and a heater applied voltage. The figure which shows the relationship between a heater deterioration level and a heater application duty.

  Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 shows the configuration of a particulate matter detection system of the present invention and an exhaust purification system 1 of an internal combustion engine to which the particulate matter detection system is applied. The exhaust purification system 1 purifies the exhaust of a diesel engine (hereinafter abbreviated as “engine”) 2 of an automobile, and is disposed upstream of the exhaust pipe 6 of the engine 2 (generic name of 6a and 6b, the exhaust passage of the present invention). The DPF 3 is disposed between the side exhaust pipe (6a) and the downstream side exhaust pipe (6b). Further, a PM sensor 4 that is a particulate matter detection system of the present invention that detects the amount of PM in the exhaust pipe 6b is disposed downstream of the DPF 3.

  For example, a ceramic filter called a wall flow type is used for the DPF 3, and the honeycomb structure of this filter is formed by alternately clogging the inlet side and the outlet side, and the exhaust from the engine 2 passes through the DPF 3. Sometimes, the exhaust that is collected in the fine holes opened in the wall surface or inside of the DPF 3 is purified. Usually, a catalyst is supported on the filter surface to promote combustion and removal of soot in the apparatus (so-called DPF with an oxidation catalyst).

  When the amount of PM deposited on the DPF 3 becomes sufficiently large, the deposited PM is removed by burning, and the DPF 3 is regenerated. The PM accumulation amount is obtained, for example, by calculating the correlation between the differential pressure across the DPF 3 and the PM accumulation amount in advance and storing it in a memory (not shown) as a data table, and arranging the differential pressure sensor, It estimates from the detected value and a data table.

  The PM sensor 4 detects the amount of PM in the exhaust downstream from the DPF 3. Since the PM sensor 4 is installed downstream of the DPF 3, it is possible to detect the amount of PM that has passed without being collected by the DPF 3 by the PM sensor 4. Thereby, the presence or absence of a failure of the DPF 3 can be detected.

  Processing such as control of valve opening timing and valve closing time of a fuel injection valve (not shown) provided in the engine 2 and regeneration / failure determination of the DPF 3 is performed by an electronic control unit 5 (ECU: Electronic Control Unit). The ECU 5 has a structure similar to that of an ordinary computer, and includes a CPU that performs various calculations, a memory that stores various information, and a peripheral circuit (not shown).

  FIG. 2 shows a configuration example of the sensor element 40 of the PM sensor 4. The sensor element 40 includes a substrate 44 (attachment portion of the present invention) made of a plate-like insulator, a pair of detection electrodes (hereinafter abbreviated as “electrodes”) 42 formed on the substrate 44, a heater 43. The entire sensor element 40 is covered with a metal cover 41, for example. One or a plurality of holes 41a are formed in the cover 41, and PM in the exhaust pipe flows into the cover 41 from the holes 41a. PM adheres and accumulates on the electrode 42 or the substrate 44 due to its own adhesiveness. Since PM has conductivity, when the pair of electrodes 42 is connected by the PM deposited on the sensor element 40, the electrodes 42 are brought into conduction.

  A voltage is applied between the electrodes 42 from a power source (not shown), and when PM is deposited on the sensor element 40 and the electrodes 42 become conductive, a current flows between the electrodes 42. The PM sensor 4 may be, for example, a measured value such as a current value (in addition, a voltage value of a certain part on the circuit, and further an impedance value (resistance value or capacitance value) calculated from the voltage value or current value). ) As a sensor output.

  As described above, even if the PM deposition amount on the surface of the sensor element 40 gradually increases, the output value of the PM sensor 4 remains zero until the electrodes 42 are electrically connected, and the electrodes 42 are electrically connected. When connected, the output value of the PM sensor 4 rises from zero according to the state. If it is determined that a large amount of PM is deposited (attached) between the electrodes 42 based on this output value, the sensor element 40 is heated by the heater 43, and the deposited PM is burned and removed to regenerate the sensor element 40. To do.

  FIG. 3 shows a more detailed configuration example of the PM sensor 4 of FIG. In addition to the sensor element 40, the electrode 42, and the heater 43, the PM sensor 4 includes a heater energization unit 45 (heater energization control unit of the present invention), a voltage detection unit 46 (detection unit of the present invention), and a control unit 49 ( The heater energization control unit and the deterioration level estimation calculation unit of the present invention are provided.

  The heater energization unit 45 adjusts the temperature of the sensor element 40 by adjusting the energization state of the heater 43 based on the heater control command from the control unit 49. The voltage detector 46 detects the voltage between the electrodes 42 and outputs it to the controller 49.

  The control unit 49 has the same structure as a normal computer, and includes a CPU (not shown) that performs various calculations, a memory 49a that stores various types of information, and peripheral circuits. It controls all controls in the PM sensor 4 such as an output of a heater control command to the heater energization unit 45 and an output of information on the PM amount attached to the sensor element 40 to the outside (for example, the ECU 5).

Note that the heater energization unit 45 may energize the heater 43 using any of the following methods.
A predetermined voltage value is applied to the heater 43 for a predetermined time (corresponding to T in FIG. 4).
When the voltage to be supplied to the heater 43 is controlled by the duty ratio of the PWM signal, a voltage having a predetermined duty ratio (for example, 50%) is applied for a predetermined time (corresponding to T in FIG. 4).
At this time, the heater 43 is heated and reaches a predetermined temperature Th.

  The heater energization voltage, energization time, and duty ratio are constant values regardless of the output voltage between the electrodes 42 during element regeneration. Thereby, the element regeneration control in the heater energization unit 45 and the control unit 49 is made more than the configuration in which the heater energization voltage or the duty ratio is made variable in accordance with the PM combustion / removal state (that is, the detection value of the voltage detection unit 46). Can be simplified. This corresponds to a configuration in which the heater energization control unit of the present invention keeps the energization state of the heater constant regardless of the output value of the sensor element when the heater is energized.

  With reference to FIG. 4, the PM adhesion amount (upper part) of the sensor element 40, the output voltage between the electrodes 42 (middle part), and the energized state of the heater 43 (lower part) at the time of regeneration of the PM sensor 4 will be described. When the PM deposition amount on the surface of the sensor element 40 exceeds the threshold value B, the control unit 49 determines that the sensor element 40 needs to be regenerated and outputs a heater control command to the heater energization unit 45. Then, the heater energization unit 45 causes the heater 43 to transition from the non-energized state to the energized state (corresponding to the state at time T1 in FIG. 4).

  When the heater 43 is energized at time T1, the output voltage between the electrodes 42 (that is, the detected value of the voltage detection unit 46: also referred to as sensor output) increases from the voltage value V0 of the state before the heater 43 is energized. At time T2, the maximum value Vmax is reached. This is due to the characteristics of soot (that is, carbon particles) which is the main component of PM attached to the sensor element 40. The soot has a characteristic that the resistance value decreases when heat is applied, and Vmax varies depending on the deterioration state of the heater 43. Thereafter, as PM burns, the output voltage between the electrodes 42 gradually decreases. And after predetermined time progress (equivalent to the state of the time T3 of FIG. 4), the heater 43 is changed from an energized state to a non-energized state. At this point, PM is combusted and removed, and the output voltage between the electrodes 42 decreases to zero (or a value close to zero).

  The PM adhesion amount B at the time of regeneration of the sensor element 40 is almost the same value each time, and the time required for regeneration of the sensor element 40 (that is, the PM removal time) is applied to the PM adhesion amount B and the heater 43. Since the voltage value can be measured or estimated in advance, the PM removal time (that is, T) is obtained by adding the time taken into consideration of the performance of the heater 43 or the variation in the PM adhesion amount B to the measured or estimated time. As a result, the PM can be reliably removed by simple control in which the heater 43 is energized at a predetermined voltage or a predetermined duty ratio without monitoring the adhesion state of the PM.

  When the heater 43 deteriorates, even if the heater 43 is energized / heated by the heater energization voltage or duty ratio, the temperature Th does not reach the temperature Th and PM cannot be completely combusted / removed.

  Although there is a method of determining deterioration by measuring the temperature of the heater 43, it is necessary to newly attach a temperature sensor to the substrate 44, and an increase in the size and cost of the substrate 44 is inevitable. When an exhaust temperature sensor is attached to the exhaust pipe 6b near the PM sensor 4, the heater temperature can be estimated based on the output value of the exhaust temperature sensor. Since the temperature fluctuates, there is a problem that the estimation process becomes complicated.

  If the heater 43 is deteriorated and the temperature does not rise to Th, the resistance value of the adhered PM is not sufficiently reduced, and Vmax in FIG. Therefore, in the present invention, attention is paid to the initial increase amount A, which is the difference between Vmax and V0 in FIG. 4, and the deterioration of the heater 43 is estimated based on the initial increase amount A.

  Specifically, the control unit 49 estimates the amount (B) of PM attached to the sensor element 40 from the detection value of the voltage detection unit 46 before energization of the heater 43. Next, Vmax generated when the heater 43 is energized is estimated from the amount. The relationship between the amount of PM (B) and Vmax may be stored in the memory 49a in advance. Then, the deterioration level of the heater 43 is estimated based on the estimated Vmax (also referred to as an ideal value) and the Vmax (also referred to as an actual measurement value) detected by the voltage detection unit 46 when the heater 43 is energized.

  With the above-described configuration, the deterioration level estimation calculation unit of the present invention estimates the amount of particulate matter adhering to the adhesion part from the detection value of the detection part before energizing the heater, and energizes the heater from that amount. The maximum value of the output of the sensor element is estimated, and the deterioration of the heater is determined based on the difference between the estimated maximum value of the PM sensor output and the maximum value of the detection value of the detection unit when the heater is energized. This corresponds to a configuration for estimating the level.

  The heater deterioration estimation process will be described with reference to FIG. This process is repeatedly executed by the control unit 49 at a predetermined timing. First, it is determined whether or not the output voltage between the electrodes 42 exceeds a predetermined value (for example, V0 in FIG. 4), that is, whether or not the sensor element 40 needs to be regenerated. When the output voltage exceeds a predetermined value (S11: Yes), a command is sent from the control unit 49 to the temperature adjusting unit 45, and the heater 43 is energized (S12).

  Next, the initial increase amount A is calculated as follows (S13). Initial increase amount A = Vmax (maximum value of output voltage between electrodes 42: actually measured value) −V0.

  Next, the heater deterioration level is estimated and calculated based on the calculated initial increase amount A (S14). That is, the value obtained by subtracting V0 from the ideal value of Vmax described above is set as the threshold A0 for the initial increase amount A. Based on the difference between the threshold value A0 and the initial increase amount A, the heater deterioration level is estimated and calculated.

  FIG. 6 shows the relationship between the heater deterioration level, the initial increase amount A, and the threshold value A0. This relationship is stored in advance in the memory 49a. In the example of FIG. 6, the heater deterioration level increases as the difference between the threshold A0 and the initial increase amount A increases, that is, as the initial increase amount A decreases. Further, two threshold values L1 (referred to as a correction determination threshold value) and L2 (referred to as a failure determination threshold value) are set for the heater deterioration level. Then, based on the comparison between the heater deterioration level and these threshold values, the heater deterioration is determined. These two threshold ranges L1 to L2 correspond to the deterioration level range of the present invention.

  Returning to FIG. 5, processing according to the heater deterioration level is executed as follows. First, when the heater deterioration level is lower than L1 (S15: Yes), it is determined that the heater 43 is normal, and correction at the time of heater energization is not performed (S16). This corresponds to a configuration in which the heater energization control unit does not correct the energization state of the heater when the deterioration level falls below a predetermined correction determination threshold. As described above, the correction determination threshold value can be, for example, the lower limit value (L1) of the deterioration level range.

  On the other hand, when the heater deterioration level is L1 or more (S15: No) and L2 or less (S17: Yes), the heater 43 energization state is corrected by any of the following methods (S18). This corresponds to a configuration in which the heater energization control unit of the present invention corrects the energization state of the heater according to the deterioration level when the heater deterioration level is included in a predetermined deterioration level range.

As shown in FIG. 7, the larger the heater deterioration level, the longer the energization time for the heater 43 is corrected. At this time, the applied voltage is not changed. If the applied voltage is increased, the temperature of the heater 43 also rises, but it is necessary to increase the withstand voltage of the heater 43 and the heater energization unit 45, and the component cost increases. On the other hand, the above-described configuration can be realized with a conventional circuit configuration, so that the component cost does not increase.

As shown in FIG. 8, correction is performed so that the duty ratio of the PWM signal applied to the heater 43 increases as the heater deterioration level increases. For example, when the heater deterioration level is L1, the duty ratio is 50% → 75%, and when the heater deterioration level is L2, the duty ratio is 50% → 90%. That is, the voltage applied to the heater 43 is increased without changing the energization time. Normally, the heater energization unit 45 is configured to operate without any problem even when the duty ratio is set to 100%, so that problems such as exceeding the withstand voltage of circuit components do not occur.

  The relationship between the heater deterioration level and the energization time or the duty ratio is stored in advance in the memory 49a as map data or a mathematical expression, for example. Then, referring to the map data, an energization time or a duty ratio corresponding to the heater deterioration level is selected, and is output from the control unit 49 to the heater energization unit 45 as a heater control command.

  On the other hand, when the heater deterioration level exceeds L2 (S19: Yes), it is determined that the heater 43 has failed, and for example, processing such as outputting information indicating that the heater 43 has failed to the ECU 5 is performed. Execute (S20). Further, the heater 43 may not be energized. This corresponds to a configuration in which the heater energization control unit does not energize the heater when the deterioration level of the heater exceeds a predetermined failure determination threshold. As described above, the failure determination threshold value can be, for example, the upper limit value (L2) of the deterioration level range.

  As shown in FIGS. 6 to 8, a new threshold value (L11, L12: the number of threshold values is arbitrary) may be set between L1 and L2, and the correction area may be subdivided to perform correction. . Thereby, finer correction can be performed.

  Although the embodiments of the present invention have been described above, these are merely examples, and the present invention is not limited to these embodiments, and the knowledge of those skilled in the art can be used without departing from the spirit of the claims. Various modifications based on this are possible.

1 Exhaust purification system 2 Diesel engine (engine, internal combustion engine)
3 Diesel particulate filter (DPF)
4 PM sensor (particulate matter detection system)
5 ECU
6 (6a, 6b) Exhaust pipe (exhaust passage)
40 Sensor element 42 Detection electrode (electrode)
43 Heater 44 Substrate (attachment)
45 Heater energization section (heater energization control section)
46 Voltage detector (detector)
49 Control unit (heater energization control unit, deterioration level estimation calculation unit)

Claims (7)

When there is an insulator attachment portion (44) provided in the exhaust passage (6b) of the internal combustion engine (2) and formed with a pair of electrodes, and particulate matter in the exhaust adheres to the attachment portion more than a certain amount A sensor element (40) that conducts between the pair of electrodes and outputs a value corresponding to the amount of particulate matter adhering to the adhering portion at the time of conduction;
A detection unit (46) for detecting a value output by the sensor element;
A heater (43) for heating and removing particulate matter adhering to the adhering portion;
A heater energization control unit (45, 49) for controlling energization of the heater;
A deterioration level estimation calculation unit (49) that estimates and calculates the deterioration level of the heater based on the detection value of the detection unit when the heater is energized;
A particulate matter detection system comprising: The deterioration level estimation calculation unit includes:
The amount of particulate matter adhering to the adhering portion is estimated from the detection value of the detecting portion before energization of the heater, and the maximum value of the output of the sensor element when energizing the heater is determined from the amount. Estimate
2. The deterioration level of the heater is estimated and calculated based on a difference between the estimated maximum value of the PM sensor output value and the maximum value of the detection value of the detection unit when the heater is energized. The particulate matter detection system described.   The particulate matter detection system according to claim 1, wherein the heater energization control unit corrects the energization state of the heater according to a deterioration level of the heater.   4. The particulate form according to claim 3, wherein when the deterioration level of the heater is included in a predetermined deterioration level range, the heater energization control unit corrects the energization state of the heater according to the deterioration level. Substance detection system.   The particulate matter detection system according to claim 4, wherein the heater energization control unit corrects the energization time to the heater to be longer as the deterioration level is larger. The heater energization control unit controls the voltage energized to the heater by the duty ratio of the PWM signal,
The particulate matter detection system according to claim 4, wherein the duty ratio is corrected so as to increase as the deterioration level increases.   The said heater energization control part keeps the energization state to the said heater constant irrespective of the output value of the said sensor element, when energizing the said heater. Particulate matter detection system.