JP2012082701A - Engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect an exhaust temperature in an easy and simple fashion in an engine having a particulate matter detecting sensor in an exhaust passage.SOLUTION: The PM (Particulate Matter) sensor 17 has: an adhesion portion on which the PM (conductive particulate matter) contained in a gas adheres; and a pair of counter electrodes provided in the adhesion portion so as to be separated from each other, and the PM sensor 17 outputs a detection signal corresponding to the resistance between a pair of the counter electrodes. A microcomputer 44 determines whether the PM adhered on the adhesion portion is combusted by the heat of the exhaust or not and if determines that the combustion of the PM by the heat of the combustion occurs, the microcomputer 44 calculates the exhaust temperature based on the variation of the sensor-detected value by the particulate matter detecting sensor upon the combustion.

Description

  The present invention relates to an engine control device, and more particularly, to an engine control device that detects an amount of particulate matter (PM) contained in exhaust gas based on a detection signal of a particulate matter detection sensor.

  Conventionally, various PM sensors (particulate matter detection sensors) for detecting the amount of PM discharged from an engine have been proposed (see, for example, Patent Document 1 and Patent Document 2). In the PM sensor of Patent Document 1, a pair of counter electrodes is provided on an insulating substrate, and the resistance between electrodes changes when PM is deposited between the pair of counter electrodes, and the interelectrode resistance is measured. In this configuration, the PM amount is detected. In this case, as a detection circuit connected to the sensor element, a voltage dividing circuit is configured by an interelectrode resistance that is a resistance between a pair of opposed electrodes and a predetermined shunt resistance, and an intermediate voltage of the voltage dividing circuit is detected by a sensor. The detection signal is output. Further, the PM sensor of Patent Document 2 has a built-in heater, and is deposited between a pair of opposed electrodes by heating with a heater for each predetermined travel distance, for each predetermined travel distance, or for each amount of fuel used. PM is burned and removed.

  Conventionally, it is known that fuel increase (high load increase) is performed to suppress damage to the exhaust system due to an increase in the exhaust temperature of the engine during high-load operation of the engine (see, for example, Patent Document 3). In Patent Document 3, in consideration of the fact that the exhaust temperature increases as the engine load increases, the fuel increase correction amount increases as the engine load increases. As a result, the exhaust temperature is lowered and damage to the exhaust system is suppressed.

JP 59-196453 A JP 2009-1444577 A JP 2006-183500 A

  When control according to the exhaust temperature such as high load increase is performed, it may be possible to directly detect the exhaust temperature by providing a temperature sensor in the exhaust pipe of the engine, but in that case, it is necessary to provide the temperature sensor. Further, the exhaust temperature may be estimated based on the engine operating state as in Patent Document 3, but in this case, an error is likely to occur between the actual exhaust temperature and the estimated temperature, and in terms of accuracy. It may be inferior.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a main object of the present invention is to provide an engine control device that can easily and accurately detect an exhaust temperature in an engine having a particulate matter detection sensor in an exhaust passage. And

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The present invention includes a portion to be attached to which conductive particulate matter contained in exhaust gas is attached, and a pair of counter electrodes provided to be separated from the portion to be attached, and a resistance value between the pair of counter electrodes. This is applied to an engine having an exhaust passage provided with a particulate matter detection sensor that outputs a detection signal according to the above. In the first aspect of the present invention, the combustion determining means for determining whether or not the particulate matter adhering to the adherend is burned by exhaust heat, and the combustion determining means performs the combustion by the exhaust heat. Exhaust gas temperature calculating means for calculating an exhaust gas temperature based on a change amount of a sensor detection value by the particulate matter detection sensor at the time of combustion when determined to have occurred.

  In the particulate matter detection sensor, the sensor detection value changes according to the amount of particulate matter attached between the pair of counter electrodes. The present invention pays attention to the fact that particulate matter adhered between a pair of counter electrodes is combusted by high-temperature exhaust heat (spontaneous combustion), and uses the behavior of the sensor detection value at the time of combustion to detect the exhaust temperature. Is calculated. That is, when the particulate matter adhering between the pair of counter electrodes burns due to the exhaust heat, the amount of attachment decreases, but at this time, of the attached particulate matter, it is used for combustion. The amount of particulate matter varies depending on the exhaust temperature. Further, the difference in the amount of particulate matter used for combustion appears as a difference in the change amount of the sensor detection value, and it is considered that the change amount of the sensor detection value increases as the exhaust gas temperature increases. Therefore, in the configuration including the particulate matter detection sensor, the exhaust temperature can be calculated by using the change amount of the sensor detection value when the particulate matter is burned by the exhaust heat as a parameter. In this case, since the exhaust temperature is calculated based on the actual combustion state of the particulate matter in the exhaust pipe, the exhaust temperature can be calculated with high accuracy.

  The invention according to claim 2 further comprises load determining means for determining whether or not the engine load is greater than a predetermined operating load, wherein the combustion determining means is configured to cause the engine load to be greater than the predetermined operating load by the load determining means. If the sensor detection value changes to the side where the resistance value increases, it is determined that combustion due to the exhaust heat has occurred, and the exhaust temperature calculation means moves to the side where the resistance value increases. The exhaust temperature is calculated based on the change amount of the sensor detection value.

  During engine operation, the particulate matter is discharged from the engine, so that the sensor detection value of the particulate matter detection sensor changes to the side where the resistance value between the pair of counter electrodes becomes smaller. In addition, when the engine operating state is a high load, the exhaust temperature may rise to a temperature at which particulate matter spontaneously burns. In such a situation, when the sensor detection value changes to the side where the resistance value between the pair of counter electrodes increases, the change is due to the particulate matter adhering between the pair of counter electrodes spontaneously combusted. It can be estimated that this is due to a decrease in the amount of adhesion. Therefore, with the above configuration, it is possible to accurately detect that spontaneous combustion of the particulate matter has occurred.

  According to a third aspect of the present invention, the exhaust gas temperature is calculated based on the amount of particulate matter adhering to the adherend when the sensor detection value changes and the amount of change in the sensor detection value.

  The particulate matter adhering to the adherend has different flammability depending on the amount of adhesion, and the more the amount of adhesion, the more likely it is to burn. Therefore, when the resistance value between the pair of counter electrodes increases due to the spontaneous combustion of the particulate matter, even if the amount of change in the resistance value is the same, the greater the amount of adhesion, the lower the actual exhaust temperature. I can judge. In view of this, the exhaust gas temperature can be calculated more accurately with the above configuration.

  According to a fourth aspect of the present invention, an exhaust gas purification device for purifying exhaust gas is provided in the exhaust passage, and fuel increase is performed to suppress overheating of the exhaust gas purification device in a high load operation region of the engine. And a high load increasing means for increasing the fuel based on the exhaust temperature calculated by the exhaust temperature calculating means.

  When the engine is heavily loaded, fuel increase (high load increase correction) may be performed to prevent damage to the exhaust emission control device due to an increase in exhaust temperature. In the high load increase correction, if the correction is excessive, the fuel consumption is deteriorated, and if the correction is insufficient, the exhaust purification device may be damaged. For this reason, it is necessary to appropriately control the fuel increase in accordance with the exhaust temperature. Here, according to the exhaust temperature calculation method based on the change amount of the sensor detection value, it is possible to calculate the temperature in a higher temperature region than the combustion temperature at which the particulate matter spontaneously burns. On the other hand, the temperature at which the exhaust purification device may be damaged is higher than the combustion temperature of the particulate matter, and is within a temperature range that can be calculated based on the change amount of the sensor detection value. Therefore, when the high load increase correction is performed based on the exhaust temperature calculated based on the change amount of the sensor detection value, it is possible to perform an appropriate fuel increase control corresponding to the exhaust temperature.

  According to a fifth aspect of the present invention, a temperature sensor for detecting an exhaust temperature is provided in the exhaust passage, and the exhaust temperature calculated by the exhaust temperature calculating means and the exhaust temperature detected by the temperature sensor are provided. It is good also as a structure which diagnoses abnormality of the said temperature sensor or the said particulate matter detection sensor based on the comparison result with temperature.

  If the temperature sensor and the particulate matter detection sensor are normal, the exhaust temperature detected by the temperature sensor and the exhaust temperature calculated based on the change amount of the sensor detection value generally coincide. On the other hand, if the difference between the exhaust temperature detected by the temperature sensor and the exhaust temperature calculated based on the change amount of the sensor detection value is large, the particulate matter detection sensor is assumed if the temperature sensor is normal. Can be diagnosed as abnormal. Further, if it is assumed that the particulate matter detection sensor is normal, it can be diagnosed that the output of the temperature sensor is abnormal.

  According to a sixth aspect of the present invention, there is provided means for determining whether or not the amount of particulate matter adhered to the adherend portion is equal to or less than a predetermined amount, and the exhaust temperature calculating means is configured such that the amount of adhesion is equal to or less than the predetermined amount. In this case, the calculation of the exhaust temperature is prohibited.

  When the amount of particulate matter attached is small, the particulate matter may not burn even if the exhaust temperature is higher than the combustion temperature of the particulate matter. In such a case, if a behavior equivalent to the change in the sensor detection value caused by spontaneous combustion is observed, there is a possibility that an output abnormality of the sensor has occurred. Therefore, when the amount of particulate matter attached is small, it is preferable not to calculate the exhaust temperature based on the change amount of the sensor detection value as in the above configuration.

The lineblock diagram showing the outline of the engine control system in a 1st embodiment. The disassembled perspective view which decomposes | disassembles and shows the principal part structure of a sensor element. The figure which shows the electrical structure regarding PM sensor. The figure which shows transition of PM detection voltage at the time of PM natural combustion. The flowchart which shows exhaust temperature calculation processing. The figure which shows an example of the map for exhaust gas temperature calculation. The flowchart which shows a high load increase correction process. The block diagram which shows the outline of the engine control system in 2nd Embodiment. The flowchart which shows the abnormality diagnosis process of a temperature sensor. The flowchart which shows the abnormality diagnosis process of PM sensor. The flowchart which shows PM forced combustion processing.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. This embodiment monitors the amount of PM (the amount of conductive particulate matter) in the exhaust discharged from the engine in a vehicle engine system including an on-vehicle engine. In particular, a PM sensor is provided in the engine exhaust pipe, and the amount of PM is monitored based on the amount of PM attached by the PM sensor. FIG. 1 is a configuration diagram showing a schematic configuration of the present system.

  In FIG. 1, an engine 11 is a direct injection gasoline engine, and a fuel injection valve 12, an ignition device 13, and the like are provided as actuators related to the operation of the engine 11. The exhaust pipe 14 of the engine 11 is provided with a three-way catalyst 15 as an exhaust purification device, an A / F sensor 16 is provided on the upstream side of the three-way catalyst 15, and particulate matter detection is provided on the downstream side. A PM sensor 17 as a sensor is provided. In addition, in this system, a rotation sensor 18 for detecting the engine rotation speed, a pressure sensor 19 for detecting the intake pipe pressure, and the like are provided.

  The ECU 20 is mainly composed of a microcomputer comprising a known CPU, ROM, RAM, etc., and executes various control programs stored in the ROM, so that the engine can be operated according to the engine operating state at each time. 11 various controls are executed. That is, the ECU 20 inputs signals from the various sensors and the like, calculates the fuel injection amount and ignition timing based on the various signals, and controls the driving of the fuel injection valve 12 and the ignition device 13.

  For fuel injection amount control, the ECU 20 calculates a basic injection amount according to, for example, the intake air amount, and performs various corrections such as post-startup increase correction, warm-up increase correction, and high load increase correction on the basic injection amount. We are carrying out. Specifically, the ECU 20 performs fuel increase correction according to the exhaust temperature in order to protect the catalyst 15 from high-temperature exhaust when the load of the engine 11 is equal to or greater than a predetermined value.

  In addition, the ECU 20 may be configured to variably control the control mode of the engine 11 based on the actual PM discharge amount (actual PM discharge amount) of the engine 11 calculated from the detection result of the PM sensor 17. For example, the fuel injection amount can be controlled based on the actual PM emission amount, the fuel injection timing can be controlled, and the ignition timing can be controlled.

  Next, the configuration of the PM sensor 17 and the electrical configuration related to the PM sensor 17 will be described with reference to FIGS. FIG. 2 is an exploded perspective view showing an essential configuration of the sensor element 31 constituting the PM sensor 17, and FIG. 3 is an electrical configuration diagram regarding the PM sensor 17.

  As shown in FIG. 2, the sensor element 31 has two insulating substrates 32 and 33 each having a long plate shape, and one insulating substrate 32 has a PM detector 34 for detecting the amount of PM. The other insulating substrate 33 is provided with a heater portion 35 for heating the sensor element 31. The sensor element 31 is configured by laminating insulating substrates 32 and 33 in two layers. The insulating substrate 32 corresponds to the adherend.

  The insulating substrate 32 is provided with a pair of detection electrodes 36a and 36b which are provided apart from each other on the surface of the substrate opposite to the other insulating substrate 33. PM detection is performed by the pair of detection electrodes 36a and 36b. Part 34 is configured. The detection electrodes 36a and 36b each have a comb shape having a plurality of comb teeth. The detection electrodes 36a and 36b are opposed to each other with a predetermined interval so that the comb teeth of the detection electrodes 36a and 36b are staggered. Moreover, the heater part 35 is comprised by the heat generating body which consists of heating wires, for example.

  However, the shape of the pair of detection electrodes 36a and 36b is not limited to the above, and a pair of detection electrodes 36a and 36b are provided in a curved shape, or a pair of electrode portions each composed of one line are parallel to each other with a predetermined distance therebetween. It may be arranged oppositely.

  Although not shown, the PM sensor 17 has a holding portion for holding the sensor element 31, and the sensor element 31 is fixed to the exhaust pipe in a state where one end side thereof is held by the holding portion. It is like that. In this case, at least a part including the PM detection unit 34 and the heater unit 35 is disposed in the exhaust pipe, and the insulating substrate 32 (PM attached portion) in the sensor element 31 faces the exhaust upstream side. The PM sensor 17 is configured to be attached to the exhaust pipe. Thus, when exhaust gas containing PM flows through the exhaust pipe, the PM adheres to and accumulates on the detection electrodes 36a and 36b and the periphery thereof on the insulating substrate 32. The PM sensor 17 has a protective cover that covers the protruding portion of the sensor element 31.

  In the PM sensor 17 configured as described above, when PM in the exhaust adheres to and accumulates on the insulating substrate 32 of the sensor element 31, the resistance value of the PM detector 34 (that is, the resistance value between the pair of detection electrodes 36a and 36b) is thereby increased. Since the change and the change in the resistance value correspond to the PM deposition amount, the change in the resistance value is used to detect the PM amount.

  As shown in FIG. 3, as an electrical configuration regarding the PM sensor 17, a sensor power supply 41 is connected to one end side of the PM detection unit 34 of the PM sensor 17, and a shunt resistor 42 is connected to the other end side. The sensor power supply 41 is constituted by a constant voltage circuit, for example, and the constant voltage Vcc is 5V. In this case, a voltage dividing circuit 40 is formed by the PM detection unit 34 and the shunt resistor 42, and an intermediate voltage between them is input to the ECU 20 as a PM detection voltage Vpm (sensor detection value). That is, in the PM detection unit 34, the resistance value Rpm changes according to the PM deposition amount, and the PM detection voltage Vpm changes depending on the resistance value Rpm and the resistance value Rs of the shunt resistor 42. The PM detection voltage Vpm is input to the microcomputer 44 via the A / D converter 43.

Here, when Vcc = 5 V and Rs = 100 kΩ, the PM detection voltage Vpm is obtained by the following equation (1).
Vpm = 5V × 100 kΩ / (100 kΩ + Rpm) (1)
At this time, if the PM deposition amount is 0 (or substantially 0), the resistance value Rpm of the PM detection unit 34 becomes infinite, so Vpm = 0V. Further, when the resistance value Rpm of the PM detection unit 34 is reduced to, for example, 1 kΩ due to PM deposition in the PM detection unit 34, Vpm = 4.95V. Thus, the PM detection voltage Vpm changes according to the amount of PM accumulated in the PM detection unit 34. The microcomputer 44 calculates the PM accumulation amount according to the PM detection voltage Vpm.

  In the PM sensor 17, a signal output circuit is configured by the voltage dividing circuit 40, and the PM detection voltage Vpm can be changed by using the voltage dividing circuit 40 with an output range of 0 to 5V. In this case, the output upper limit value of the PM detection voltage Vpm is 5V, more strictly, a voltage value slightly lower than 5V.

  A heater power supply 45 is connected to the heater unit 35 of the PM sensor 17. The heater power supply 45 is, for example, an in-vehicle battery, and the heater unit 35 is heated by power supply from the in-vehicle battery. In this case, a transistor 46 as a switching element is connected to the low side of the heater unit 35, and heating control of the heater unit 35 is performed by the transistor 44 being turned on / off by the microcomputer 44.

  When energization of the heater unit 35 is started in a state where PM is deposited on the insulating substrate 32, the temperature of the deposited PM rises, and the deposited PM is forcibly burned accordingly. Due to such forced combustion, PM deposited on the insulating substrate 32 is removed by combustion. The microcomputer 44, for example, when it is determined that the PM deposition amount on the insulating substrate 32 has become a predetermined amount, or when it is determined that the engine operating time or the vehicle travel distance from the previous PM forced combustion has reached a predetermined value. Then, the heating control by the heater unit 35 is performed assuming that a forced combustion request for PM is generated. In particular, in the present embodiment, heating control by the heater unit 35 is performed on the assumption that a PM forced combustion request is generated when the engine is stopped.

  In addition, the ECU 20 is provided with an EEPROM 47 as a backup memory for storing various learning values, abnormality diagnosis values (diagnostic data), and the like.

  Now, the PM deposited on the PM sensor 17 may be naturally combusted by being heated to high temperature by the exhaust heat. In the present embodiment, attention is paid to the behavior in which the PM detection voltage Vpm changes due to the spontaneous combustion of PM, and the exhaust gas temperature is calculated based on the change in the PM detection voltage Vpm when the deposited PM spontaneously burns.

  That is, as shown in FIG. 4, in the engine operating state, the PM detection voltage Vpm gradually increases as PM is discharged from the engine 11. At this time, for example, when the engine 11 is at a high load, the exhaust temperature Due to the rise, the PM deposited on the insulating substrate 32 may rise in temperature and self-ignite even though the heater substrate 35 is not heating the insulating substrate 32. Further, when PM is combusted (spontaneous combustion) with self-ignition due to exhaust heat, the PM sensor 17 causes an output decrease corresponding to the amount of PM removed by combustion. Here, when PM is combusted by natural combustion, the amount of PM that is provided for combustion out of the PM that adheres to the insulating substrate 32 differs according to the exhaust temperature. The higher the exhaust temperature, the more PM is provided for combustion. Become more. As a result, the output reduction amount ΔV accompanying natural combustion increases as the exhaust gas temperature increases. In the present embodiment, focusing on the fact that the above behavior appears during PM natural combustion, the exhaust gas temperature is calculated based on the amount of change in the PM detection voltage Vpm during PM natural combustion.

  Next, the exhaust gas temperature calculation process of the present embodiment will be described using the flowchart of FIG. This process is executed at predetermined intervals by the microcomputer 44 of the ECU 20.

  In FIG. 5, in step S10, it is determined whether or not the engine 11 is in a predetermined high load state. Here, it is determined whether or not the current engine load is larger than a load L1 that is likely to rise to a temperature at which PM spontaneous combustion occurs (PM combustion temperature). When step S10 is NO, the exhaust temperature is not calculated based on the amount of change in the PM detection voltage Vpm, and this routine is terminated as it is.

  On the other hand, if step S11 is YES, the process proceeds to step S12, and the previous value Vpm (k-1) and current value Vpm (k) of the PM detection voltage are read, and the combustion processing execution flag Xpmb is read. Here, the combustion processing execution flag Xpmb is a flag that is turned on when the combustion of the deposited PM by the heater 35 is being executed.

  In a succeeding step S12, it is determined whether or not the combustion processing execution flag Xpmb is OFF. If Xpmb = OFF, the process proceeds to step S13, and the previous value Vpm (k-1) is compared with the current value Vpm (k). When the previous value Vpm (k-1) is larger than the current value Vpm (k), that is, when the PM detection voltage Vpm is lowered, the process proceeds to step S14, and the exhaust temperature calculation flag Xest is turned ON. The exhaust gas temperature calculation flag Xest is a flag that is turned on when permitting calculation of the exhaust gas temperature using the PM detection voltage Vpm. In step S15, the integrated value obtained by subtracting the current value Vpm (k) from the previous value Vpm (k-1), that is, the voltage change amount after the PM detection voltage Vpm starts to decrease is stored as the output decrease amount ΔV. To do. Then, this routine is temporarily terminated.

  When the PM detection voltage Vpm turns from a decrease to an increase, step S13 becomes NO, and the process proceeds to step S17. In step S17, it is determined whether or not the exhaust temperature calculation flag Xest is ON. If Xset = ON, the process proceeds to step S18, and the exhaust temperature (PM sensor exhaust temperature) Tex is calculated based on the output decrease amount ΔV. Here, the exhaust temperature Tex corresponding to the output decrease amount ΔV is obtained using the exhaust temperature calculation map.

  FIG. 6 is a diagram illustrating an example of an exhaust temperature calculation map. According to the temperature calculation method based on the output decrease amount ΔV of the present embodiment, it is possible to calculate the temperature in a temperature range equal to or higher than the PM combustion temperature Tpm or a predetermined temperature (Tpm + α) slightly higher than the PM combustion temperature Tpm. As shown in FIG. 6, the exhaust gas temperature Tex is set to a higher value as the output decrease amount ΔV is larger. In particular, in this embodiment, the relationship between the output decrease amount ΔV and the exhaust temperature Tex is determined according to the PM accumulation amount. Specifically, the exhaust temperature Tex for the same output decrease amount ΔV increases as the PM accumulation amount increases. It is set to be low. This is because the greater the amount of PM deposited, the easier it is to burn, and the lower the output, the greater the amount of PM deposited, even if the exhaust temperature is the same.

  Returning to the description of FIG. 5, in step S19, a flag (output use prohibition flag) Xpmi for setting prohibition of use of the PM detection voltage Vpm is turned ON, and a PM combustion processing start flag Xpmr is turned ON. In other words, in this embodiment, when the PM spontaneously burns, the use of the PM detection voltage Vpm is prohibited, and the forced combustion of the PM deposited on the insulating substrate 32 is performed by another routine (not shown). . As a result, the PM deposition amount on the insulating substrate 32 is reset to zero. Note that the PM forced combustion process may be performed after the engine load becomes equal to or lower than a predetermined medium to low load. In step S19, the output decrease amount ΔV is reset to zero. Thereafter, in step S20, the exhaust temperature calculation flag Xest is turned OFF, and this routine is terminated.

  In the present embodiment, fuel injection amount control, specifically, high load increase correction, is performed using the exhaust temperature calculated by the exhaust temperature calculation process. Hereinafter, the high load increase correction will be described.

  FIG. 7 is a flowchart showing a high load increase correction process. This process is executed at predetermined intervals by the microcomputer 44 of the ECU 20.

  In FIG. 7, in step S30, it is determined whether or not the engine load is larger than a predetermined load L2. The predetermined load L2 is determined based on a load that needs to be protected to avoid melting of the catalyst 15, and is set equal to or larger than the predetermined load L1. If the engine load is greater than the predetermined load L2, the process proceeds to step S31, where it is determined whether or not the current exhaust temperature Tex has been calculated by the above exhaust temperature calculation process, and the exhaust temperature Tex has been calculated. If there is, the process proceeds to step S32.

  In step S32, the calculated current exhaust gas temperature Tex is read. In step S33, it is determined whether the exhaust gas temperature Tex is higher than the catalyst limit temperature Tcath. The catalyst limit temperature Tcath is determined based on the temperature at which the catalyst 15 may be melted, and is set on the higher temperature side than the PM combustion temperature Tpm. Then, if step S33 is NO, this routine is ended as it is, and if step S33 is YES, the process proceeds to step S34, and the correction amount of the fuel increase is calculated according to the exhaust temperature Tex. Here, the correction amount is set so that the fuel increase is increased as the exhaust temperature Tex is higher. The correction amount calculated here is used when correcting the basic injection amount in the fuel injection amount calculation processing by another routine (not shown).

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  Since the exhaust temperature is calculated based on the amount of change in the PM detection voltage Vpm when the PM adhering to the PM sensor 17 spontaneously burns, the exhaust temperature can be obtained without providing a means for directly detecting the exhaust temperature, such as a temperature sensor. Can be calculated. Further, since the exhaust gas temperature is calculated based on the actual PM combustion state in the exhaust pipe 14, the exhaust gas temperature can be calculated with higher accuracy than when estimated from the engine operating state, for example.

  Since the engine load is larger than the load L1 and when the PM detection voltage Vpm is reduced, it is determined that PM spontaneous combustion has occurred. Therefore, it is possible to accurately detect that PM spontaneous combustion has occurred. . Conversely, when the engine load is less than or equal to the load L1, the amount of change in the PM detection voltage Vpm is considered in consideration that the exhaust temperature does not become so high that spontaneous combustion of PM occurs and natural combustion should not occur. Therefore, the exhaust temperature calculation accuracy can be prevented from being lowered.

  The PM adhering to the insulating substrate 32 has different flammability depending on the amount of adhesion. The larger the amount of adhering, the more likely it is to burn, and on the insulating substrate 32 when the PM detection voltage Vpm decreases. Since the exhaust temperature is calculated based on the PM adhesion amount and the output decrease amount ΔV, the upper exhaust temperature can be calculated more accurately.

  Since the high load increase correction is performed based on the exhaust temperature calculated based on the output decrease amount ΔV during PM natural combustion, even in a system in which the temperature sensor is not provided in the exhaust pipe 14, an appropriate value corresponding to the exhaust temperature is used. Fuel increase control can be performed.

(Second Embodiment)
In the above embodiment, the description has been given of performing the high load increase correction using the exhaust temperature (PM sensor exhaust temperature) Tex calculated by the exhaust temperature calculation processing of FIG. 5, but in this embodiment, in the exhaust pipe of the engine, In addition to the PM sensor, a temperature sensor for detecting the exhaust temperature is provided, and an output abnormality of the temperature sensor is diagnosed based on the PM sensor exhaust temperature Tex and the exhaust temperature (temperature sensor exhaust temperature) detected by the temperature sensor. . Hereinafter, the difference from the above embodiment will be mainly described.

  FIG. 8 is a configuration diagram showing an outline of the engine control system in the present embodiment. In FIG. 8, the exhaust pipe 14 of the engine 11 is provided with a temperature sensor 21 having a temperature detection element on the downstream side of the catalyst 15. The temperature sensor 21 may be arranged on the upstream side of the catalyst 15. The ECU 20 receives a detection signal from the temperature sensor 21 and performs various controls of the engine 11 based on the detection signal.

  Next, abnormality diagnosis processing of the temperature sensor 21 will be described with reference to the flowchart of FIG. This process is executed at predetermined intervals by the microcomputer 44 of the ECU 20. The normal output of the PM sensor 17 has been diagnosed by another routine (not shown).

  In FIG. 9, in step S40, it is determined whether the current PM sensor exhaust temperature Tex has been calculated by the exhaust temperature calculation processing of FIG. 5, and if the PM sensor exhaust temperature Tex has been calculated, the process proceeds to step S41. move on. In step S41, the calculated current PM sensor exhaust temperature Tex is read. In step S42, the temperature sensor exhaust temperature Teg, which is a detection value of the temperature sensor 21, is read.

  In step S43, a difference (absolute value) between the PM sensor exhaust temperature Tex and the temperature sensor exhaust temperature Teg is obtained, and it is determined whether or not the difference is larger than the abnormality determination value Tdiag. At this time, if the difference is equal to or less than the abnormality determination value Tdiag, the process proceeds to step S44, and it is determined that the output of the temperature sensor 21 is normal. Specifically, the temperature sensor normal flag Xegok is turned on and the temperature sensor abnormality flag Xegfa is turned off. On the other hand, if the difference is larger than the abnormality determination value Tdiag, the process proceeds to step S45 to determine that the output of the temperature sensor 21 is abnormal. Specifically, the temperature sensor normal flag Xegok is turned off, and the temperature sensor abnormality flag Xegfa is turned on. In this case, abnormality diagnosis data (diagnostic data) indicating an output abnormality of the temperature sensor 21 is stored in the EEPROM 47.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  Since the exhaust temperature (PM sensor exhaust temperature Tex) is calculated based on the output decrease amount ΔV during PM natural combustion, the calculated PM sensor exhaust temperature Tex and the temperature sensor exhaust temperature detected by the temperature sensor 21 are used. By comparing Teg, the output abnormality of the temperature sensor 21 can be diagnosed.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  When the amount of PM adhering on the insulating substrate 32 is equal to or less than a predetermined amount, calculation of the exhaust temperature based on the amount of change in the PM detection voltage Vpm is prohibited. When the PM adhesion amount is small, PM combustion may not occur even when the exhaust temperature is higher than the PM combustion temperature. This is because, in such a case, if the sensor output decreases, an abnormal output of the sensor may occur. Further, when the sensor output decreases when the amount of PM adhering on the insulating substrate 32 is equal to or less than the predetermined amount, the output abnormality of the PM sensor 17 is represented as an abnormality of the output of the PM sensor 17. Abnormality diagnosis data (diag data) may be stored in the EEPROM 47.

  An abnormality in the output of the PM sensor 17 is diagnosed using a determination result of the presence or absence of natural combustion based on the amount of change in the PM detection voltage Vpm in an intermediate / low load operation region where the engine load is a predetermined load or less. Normally, in the middle and low load operation region, the exhaust gas temperature does not rise to the PM combustion temperature, so that the spontaneous combustion of the deposited PM should not occur. Using this premise, in this configuration, when it is determined that natural combustion is present based on the amount of change in the PM detection voltage Vpm even though the engine load is equal to or less than the predetermined load, the output abnormality of the PM sensor 17 is abnormal. Is determined to have occurred.

  FIG. 10 shows a flowchart of PM sensor abnormality diagnosis processing. In addition, about the process similar to the said FIG. 5, the same step number as FIG. 5 is attached | subjected and the description is abbreviate | omitted. In FIG. 10, in steps S51 to S53, the same processing as in steps S11 to S13 of FIG. 5 is executed, and if steps S52 and S53 are YES, the process proceeds to step S54. In step S54, it is determined whether or not the engine load is smaller than a predetermined load L3. The predetermined load L3 may be the same value as the load L1 or a different value. If step S54 is NO, it is determined in step S55 that the output of the PM sensor 17 is normal. On the other hand, when step S54 is YES, it progresses to step S56 and determines with the output of PM sensor 17 being abnormal. In this case, abnormality diagnosis data (diag data) indicating output abnormality of the PM sensor 17 is stored in the EEPROM 47.

  In the above embodiment, the PM sensor exhaust temperature Tex calculated based on the change amount of the PM detection voltage Vpm is used for the high load fuel increase or the abnormality diagnosis of the temperature sensor 21, but the control using the PM sensor exhaust temperature Tex is used for these. Not limited. For example, in a configuration in which a PM filter for collecting PM is provided in the exhaust pipe 14 of the engine 11 and the PM sensor 17 is provided on at least one of the downstream side and the upstream side thereof, the PM is based on the PM sensor exhaust temperature Tex. Controls the regeneration timing of the filter. In this case, in the regeneration process of the PM filter, it is possible to suppress the filter damage due to the excessive temperature rise of the PM filter, and it is possible to suppress the regeneration from being insufficient due to the filter temperature being too low.

  In the configuration in which the PM filter is arranged in the exhaust pipe 14, when the PM sensor is being regenerated and the PM sensor exhaust temperature Tex calculated based on the amount of change in the PM detection voltage Vpm is equal to or higher than a predetermined temperature, the PM The sensor 17 is configured to perform forced combustion processing.

  FIG. 11 is a flowchart showing the PM forced combustion process. This process is executed at predetermined intervals by the microcomputer 44 of the ECU 20. In FIG. 11, in step S61, it is determined whether or not the PM sensor exhaust temperature Tex has been calculated. If it has been calculated, the process proceeds to step S62, where the PM sensor exhaust temperature Tex, the combustion processing execution flag Xpmb, and filter regeneration are performed. The processing execution flag Xfil is read. Here, the filter regeneration process in progress flag Xfil is a flag that is turned on during the execution of the regeneration process of the PM filter. In the following step S63, it is determined whether or not the combustion process execution flag Xpmb and the filter regeneration process execution flag Xfil are ON. If step S63 is YES, the process proceeds to step S64, and the PM sensor exhaust temperature Tex is predetermined. It is determined whether or not the temperature is equal to or higher than Tth. If step S64 is YES, the process proceeds to step S65 where the output use prohibition flag Xpmi is turned on and the PM combustion process start flag Xpmr is turned on. As a result, the use of the PM detection voltage Vpm is prohibited, and the PM deposited on the insulating substrate 32 is forcibly burned by another routine (not shown), and the amount of PM deposited on the insulating substrate 32 is reset to zero. .

  In the second embodiment, the abnormality diagnosis of the temperature sensor 21 is performed using the PM sensor exhaust temperature Tex calculated based on the change amount of the PM detection voltage Vpm on the assumption that the output of the PM sensor 17 is normal. However, conversely, on the assumption that the output of the temperature sensor 21 is normal, an abnormality diagnosis of the PM sensor 17 may be performed using the PM sensor exhaust temperature Tex.

In the above embodiment, the voltage dividing circuit 40 shown in FIG. 3 is used as the signal output circuit, but this may be changed. For example, the PM detector 34 and the shunt resistor 42 constituting the voltage dividing circuit may be reversely connected, and the PM detector 34 may be provided on the low side and the shunt resistor 42 may be provided on the high side. In this configuration, the PM detection voltage Vpm is obtained by the following equation (2).
Vpm = 5V × Rpm / (Rs + Rpm) (2)
Rpm is the resistance value of the PM detector 34, and Rs is the resistance value of the shunt resistor 42 (for example, 5 kΩ).

  -In the above-mentioned embodiment, although application about a direct-injection type gasoline engine was illustrated, it is applicable also to other types of engines. For example, the present invention can be applied to a diesel engine (particularly, a direct injection type diesel engine), and the present invention can be used for a PM sensor provided in an exhaust pipe of the diesel engine. Alternatively, the PM amount may be detected for a gas other than the engine exhaust.

  DESCRIPTION OF SYMBOLS 11 ... Engine, 15 ... Catalyst (exhaust gas purification device), 17 ... PM sensor (particulate matter detection sensor), 20 ... ECU, 32 ... Insulating substrate (attachment part), 34 ... PM detection part, 35 ... Heater part, 36a, 36b ... detection electrode (counter electrode), 40 ... voltage dividing circuit, 41 ... sensor power supply, 42 ... shunt resistance, 44 ... microcomputer (combustion judging means, exhaust temperature calculating means, load judging means, high load increasing means, abnormal Diagnostic means).

Claims (6)

Detection according to a resistance value between the pair of counter electrodes, which includes a portion to be adhered to which conductive particulate matter contained in the exhaust is adhered, and a pair of counter electrodes that are provided apart from each other in the portion to be adhered. Applied to an engine equipped with an exhaust passage with a particulate matter detection sensor that outputs a signal,
Combustion determination means for determining whether combustion due to exhaust heat has occurred for the particulate matter adhering to the adherend portion;
An exhaust temperature calculating means for calculating an exhaust temperature based on a change amount of a sensor detection value by the particulate matter detection sensor at the time of combustion when it is determined by the combustion determining means that combustion by the exhaust heat has occurred; ,
An engine control device comprising: Load determining means for determining whether the engine load is greater than a predetermined operating load;
The combustion determination means determines that the engine load is determined to be larger than a predetermined operation load by the load determination means, and combustion due to the exhaust heat occurs when the sensor detection value changes to the side where the resistance value increases. And
The engine control apparatus according to claim 1, wherein the exhaust temperature calculation means calculates an exhaust temperature based on a change amount of the sensor detection value toward a side where the resistance value increases.   The exhaust gas temperature calculation means calculates an exhaust gas temperature based on the amount of particulate matter adhered to the adherend when the sensor detection value changes and the amount of change in the sensor detection value. Or the engine control apparatus of 2. In the exhaust passage, an exhaust purification device for purifying exhaust is provided,
In a high load operation region of the engine, comprising high load increase means for increasing the fuel to suppress overheating of the exhaust purification device,
The engine control apparatus according to any one of claims 1 to 3, wherein the high load increasing means increases the fuel based on the exhaust temperature calculated by the exhaust temperature calculating means. In the exhaust passage, a temperature sensor for detecting the exhaust temperature is provided,
An abnormality diagnosis unit that diagnoses an abnormality of the temperature sensor or the particulate matter detection sensor based on a comparison result between the exhaust temperature calculated by the exhaust temperature calculation unit and the exhaust temperature detected by the temperature sensor. The engine control device according to any one of 1 to 4. Means for determining whether or not the amount of particulate matter adhered to the adherend portion is a predetermined amount or less;
The engine control apparatus according to any one of claims 1 to 5, wherein the exhaust temperature calculation means prohibits calculation of an exhaust temperature when the amount of adhesion is equal to or less than the predetermined amount.

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