WO2016103398A1

WO2016103398A1 - Exhaust sensor management device and management method

Info

Publication number: WO2016103398A1
Application number: PCT/JP2014/084323
Authority: WO
Inventors: 茂己小林; 今野　浩之; 林　哲久
Original assignee: ボルボトラックコーポレーション; 茂己小林; 今野　浩之; 林　哲久
Priority date: 2014-12-25
Filing date: 2014-12-25
Publication date: 2016-06-30

Abstract

An exhaust sensor management device includes an exhaust sensor for detecting one state quantity of engine exhaust characteristics, and a control unit incorporating a microcomputer. The control unit estimates the one state quantity of the engine exhaust characteristics on the basis of an engine operation state. The control unit also diagnoses a degradation level of the exhaust sensor on the basis of a comparison between the detected state quantity and the estimated state quantity.

Description

Exhaust sensor management device and management method

The present invention relates to an exhaust sensor management apparatus and management method.

In vehicles such as automobiles, for example, nitrogen oxide (NOx) concentration, oxygen (O ₂ ) concentration, air-fuel ratio (A / F), etc. in exhaust gas are detected in order to suppress harmful substances in exhaust gas to below the reference level. The fuel injection amount of the engine is electronically controlled based on the output signal of the exhaust sensor. In this case, if an abnormality occurs in the exhaust sensor, harmful substances in the exhaust may exceed the reference level. Therefore, as described in JP 2010-180843 A (Patent Document 1), Techniques for diagnosing the presence or absence of abnormalities have been proposed.

JP 2010-180843 A

By the way, since the exhaust sensor is exposed to exhaust gas, for example, the deterioration level slowly proceeds due to exhaust heat, poisoning due to impurities, and the like. However, since the conventional technology cannot grasp the deterioration level of the exhaust sensor, if the deterioration level of the exhaust sensor progresses to some extent, the detection accuracy decreases, and it becomes difficult to maintain the harmful substances in the exhaust below the reference level. End up.

Therefore, an object of the present invention is to provide an exhaust sensor management device and a management method capable of grasping the deterioration level of the exhaust sensor.

For this reason, a control unit capable of reading the output of an exhaust sensor that detects one state quantity of the engine exhaust property estimates and detects one state quantity of the engine exhaust property based on the operating state of the engine. The deterioration level of the exhaust sensor is diagnosed based on a comparison between the state quantity and the estimated state quantity.

According to the present invention, the deterioration level of the exhaust sensor can be grasped.

It is a schematic diagram showing an example of an engine system. It is an external view which shows an example of a NOx sensor. It is principal part sectional drawing which shows an example of a NOx sensor. It is a block diagram which shows an example of a control unit. It is a flowchart which shows an example of the main routine which performs a sensor management process. It is a flowchart which shows an example of the subroutine which performs a deterioration level diagnosis. It is explanatory drawing of the deterioration state of a NOx sensor. It is explanatory drawing of the deterioration state at the time of making a NOx sensor pause. It is explanatory drawing of the deterioration state at the time of cooling when a NOx sensor is made to rest. It is sectional drawing which shows an example of DPF.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of an engine system mounted on a vehicle such as a truck.

In the intake pipe 120 connected to the intake manifold 110 of the diesel engine 100, an air cleaner 130, a compressor 142 of the turbocharger 140, an intercooler 150, and an intake throttle 160 are arranged in this order along the intake air circulation direction. .

The air cleaner 130 removes dust and the like in the air with an air element (not shown) built in the casing. The turbocharger 140 supercharges the intake air that has passed through the air cleaner 130 with a compressor 142 that rotationally drives using exhaust energy. The intercooler 150 cools the intake air that has passed through the compressor 142 of the turbocharger 140 using, for example, traveling wind and cooling water. The intake throttle 160 reduces vibration generated when the diesel engine 100 is stopped, for example, by restricting intake air when the diesel engine 100 is stopped.

In the exhaust pipe 180 connected to the exhaust manifold 170 of the diesel engine 100, a turbine 144 of the turbocharger 140, a continuously regenerating diesel particulate filter (DieselicParticulate Filter, hereinafter referred to as “DPF”) is arranged along the exhaust flow direction. The apparatus 190, the SCR (Selective Catalytic Reduction) converter 200, and the oxidation catalytic converter 210 are arranged in this order.

The continuous regeneration type DPF device 190 collects and removes a DOC (Diesel Oxidation Catalyst) converter 192 that oxidizes at least NO (nitrogen monoxide) into NO ₂ (nitrogen dioxide) and PM (Particulate Matter) in the exhaust gas. DPF 194 to be included. Here, as the DPF 194, a CSF (Catalyzed Soot Filter) in which a catalyst (active component and additive component) is supported on the surface thereof can also be used. The SCR converter 200 uses Fe (iron) or Ce (cerium) as an active species and receives, for example, supply of ammonia functioning as a reducing agent, and selectively reduces and purifies NOx in the exhaust gas. The oxidation catalytic converter 210 oxidizes the reducing agent that has passed through the SCR converter 200.

An injection nozzle 220 for injecting and supplying a urea aqueous solution as an example of a liquid reducing agent precursor is attached to the exhaust pipe 180 positioned between the continuous regeneration type DPF device 190 and the SCR converter 200. The urea aqueous solution stored in the reducing agent tank 230 is supplied to the injection nozzle 220 via the reducing agent adding device 240 having at least a pump and a flow rate control valve built therein. Here, the reducing agent adding device 240 may be divided into two parts: a pump module having at least a pump and a dosing module having at least a flow rate control valve.

Also, the diesel engine 100 is equipped with an EGR (Exhaust Gas Recirculation) system 250 that reduces NOx by lowering the combustion temperature by introducing a part of the exhaust gas into the intake system and recirculating it. The EGR system 250 includes an EGR pipe 252 for introducing a part of the exhaust gas flowing through the exhaust pipe 180 into the intake pipe 120, an EGR cooler 254 for cooling the exhaust gas (EGR gas) flowing through the EGR pipe 252, and the intake pipe 120. And an EGR control valve 256 for controlling the EGR rate of the EGR gas to be introduced. Here, the EGR control valve 256 is disposed downstream of the EGR cooler 254, that is, at a location where the EGR gas that has passed through the EGR cooler 254 is introduced into the intake pipe 120.

Furthermore, the diesel engine 100 is connected to both ends of a cooling water pipe 270 provided with a radiator 260 so as to communicate, for example, a cooling water inlet and a cooling water outlet formed in the cylinder head.

An exhaust pipe 180 positioned between the continuous regeneration type DPF device 190 and the injection nozzle 220 includes a temperature sensor 280 for detecting the temperature (exhaust temperature) Te of the exhaust, and a first NOx sensor for detecting the NOx concentration C in the exhaust. 290, respectively. Further, a second NOx sensor 300 for detecting the NOx concentration C in the exhaust is attached to the exhaust pipe 180 located downstream of the oxidation catalytic converter 210. Furthermore, a rotational speed sensor 310 that detects the rotational speed Ne of the diesel engine 100, a load sensor 320 that detects the load Q of the diesel engine 100, and an intake air humidity (intake humidity) H are detected at predetermined locations of the vehicle. A humidity sensor 330 is attached to each. Here, as the load Q of the diesel engine 100, for example, a state quantity closely related to the torque, such as a fuel injection amount, an accelerator opening degree, an intake air flow rate, and a supercharging pressure can be used. Moreover, in the following description, when it is not necessary to distinguish between the first NOx sensor 290 and the second NOx sensor 300, these are represented as the NOx sensor 290 as a representative.

As shown in FIG. 2, the NOx sensor 290 includes a sensor body 292 having a concentration detection unit 292A built in the tip, a controller 294 that controls the operation of the concentration detection unit 292A and converts the output voltage into a concentration signal. And a connector 296 for connecting to a control system of the vehicle. The sensor body 292 and the controller 294, and the controller 294 and the connector 296 are connected by a cable 298 including a power supply line, a signal line, and the like, respectively.

As shown in FIG. 3, the sensor body 292 includes a density detector 292A and a metal cover 292B that covers the periphery of the density detector 292A. The concentration detection unit 292A outputs a voltage signal that is substantially proportional to the NOx concentration in the exhaust gas by using, for example, oxygen ion conductivity of zirconia (ZrO ₂ ). On the other hand, the peripheral wall of the cover 292B is formed with a plurality of exhaust outlets 292C for introducing exhaust into the internal space and leading out the exhaust from the internal space.

Specifically, the concentration detection unit 292A includes a laminated structure of zirconia solid electrolyte, and has two internal spaces, three oxygen pumps, and a heater. A pair of electrodes functioning as a first oxygen pump is disposed in the first space, and by applying a predetermined voltage between the electrodes, oxygen is removed from the first space and a combustible gas (HC, CO) is obtained. , H ₂ ) to make the oxygen concentration level of several ppm in the first space. A second oxygen pump and a measurement pump are arranged in the second space arranged at the back of the first space, and after removing oxygen from the second space by the second oxygen pump, NO is converted into O ₂ and N _The oxygen partial pressure proportional to the NOx concentration in the exhaust gas is measured with a measuring pump. The heater of the concentration detector 292A maintains the zirconia solid electrolyte at a predetermined activation temperature or higher.

A plurality of Peltier elements 292D are attached to the outer periphery of the concentration detector 292A and extend outward from the concentration detector 292A so as to come into contact with the inner peripheral surface of the cover 292B. Each Peltier element 292D is connected to the driver of the controller 294 via a pair of wiring patterns 292E printed on the density detection unit 292A. For this reason, the concentration detector 292A can be cooled or the concentration detector 292A can be heated by changing the polarity of the voltage applied to the Peltier element 292D by the controller 294. Here, since the concentration detection unit 292A and the cover 292B are thermally connected via the Peltier element 292D, the cover 292B not only protects the concentration detection unit 292A but also serves as a heat sink for heat dissipation, for example. It can also function. Note that the Peltier element 292D is an example of a thermoelectric conversion element.

Further, the NOx sensor 290 has a built-in or attached temperature sensor (not shown) for detecting the temperature (sensor temperature) Ts of the concentration detection unit 292A. The output signal of this temperature sensor is output together with the NOx concentration C.

The output signals of the temperature sensor 280, the first NOx sensor 290, the second NOx sensor 300, the rotation speed sensor 310, the load sensor 320 and the humidity sensor 330 are input to a control unit 340 incorporating a microcomputer. As shown in FIG. 4, the control unit 340 includes a processor A such as a CPU (Central Processing Unit), a nonvolatile memory B such as a flash ROM (Read Only Memory), and a volatile memory such as a RAM (Random Access Memory). C, an input / output circuit D serving as an interface with an external device, and a bus E that connects these to each other so as to communicate with each other.

The control unit 340 obtains an EGR amount corresponding to the rotational speed Ne and the load Q, and outputs an operation amount corresponding to the EGR amount to the EGR control valve 256, thereby electronically controlling the EGR system 250. Further, the control unit 340 obtains the urea aqueous solution addition amount according to the exhaust temperature Te, the rotational speed Ne, and the load Q, and outputs an operation amount according to the addition amount to the reducing agent addition device 240, thereby enabling the diesel engine 100 exhaust emission control devices are electronically controlled. At this time, the control unit 340 obtains the NOx purification rate based on the NOx concentration C upstream of the SCR converter 200 and the NOx concentration C downstream of the oxidation catalyst converter 210, and the amount of urea aqueous solution added is determined according to the NOx purification rate. It can be corrected.

Further, the control unit 340 diagnoses the deterioration levels of the first NOx sensor 290 and the second NOx sensor 300, and electronically controls the alarm device 350 and the monitor 360, respectively, and delays the progress of the deterioration level according to the diagnosis results. Perform as necessary. Here, as the alarm 350, for example, a buzzer, a warning light, or the like can be used. As the monitor 360, for example, a monitor of a navigation system, a multi-information display, or the like can be used.

In such an engine system, the exhaust of the diesel engine 100 is introduced into the DOC converter 192 of the continuous regeneration type DPF device 190 through the exhaust manifold 170 and the turbine 144 of the turbocharger 140. The exhaust gas introduced into the DOC converter 192 flows to the DPF 194 while NO is oxidized to NO ₂ . In the DPF 194, PM in the exhaust gas is removed, and PM is continuously oxidized (incinerated) using NO ₂ generated by the DOC converter 192.

Further, the urea aqueous solution supplied (added) from the injection nozzle 220 according to the engine operating state is hydrolyzed using exhaust heat and water vapor in the exhaust, and converted into ammonia that functions as a reducing agent. It is known that this ammonia is selectively reduced with NOx in the exhaust gas in the SCR converter 200 and purified to harmless H ₂ O (water) and N ₂ (nitrogen). At this time, NO is oxidized to NO ₂ by the DOC converter 192, and the ratio of NO to NO ₂ in the exhaust gas is improved to be suitable for the selective reduction reaction, so that the NOx purification rate in the SCR converter 200 is improved. be able to. On the other hand, the ammonia that has passed through the SCR converter 200 is oxidized by the oxidation catalytic converter 210 disposed downstream of the exhaust gas, so that the ammonia can be prevented from being released into the atmosphere as it is.

FIG. 5 shows an example of sensor management processing for the first NOx sensor 290 and the second NOx sensor 300, which is repeatedly executed by the processor A of the control unit 340 when the control unit 340 is activated. The processor A of the control unit 340 executes sensor management processing for each of the first NOx sensor 290 and the second NOx sensor 300 in accordance with, for example, a control program stored in the nonvolatile memory B.

In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the processor A of the control unit 340 executes a subroutine (FIG. 6) for diagnosing the deterioration level of the NOx sensor 290. Here, the subroutine for diagnosing the deterioration level of the NOx sensor 290 calculates, for example, a deterioration level that represents the deterioration from the unused state as a numerical value in order to express the deterioration level objectively.

In step 2, the processor A of the control unit 340 determines whether or not the deterioration level of the NOx sensor 290 has reached the predetermined level Ld, that is, whether or not the deterioration level has become higher than the predetermined level Ld. Here, the predetermined level Ld is a threshold value for determining that the deterioration level of the NOx sensor 290 has progressed and the replacement time of the NOx sensor 290 is approaching. For example, the design level of the NOx sensor 290 is considered. Can be determined. If the processor A of the control unit 340 determines that the deterioration level has reached the predetermined level Ld (Yes), the process proceeds to step 3. On the other hand, if the processor A of the control unit 340 determines that the deterioration level has not reached the predetermined level Ld (No), the processor A ends the processing.

In step 3, the processor A of the control unit 340 activates the notification device 350 to notify that the deterioration level of the NOx sensor 290 has progressed to some extent, that is, that the replacement time of the NOx sensor 290 is approaching. Further, the processor A of the control unit 340 estimates the distance that the NOx sensor 290 can travel before reaching the end of its life based on the deterioration level, and causes the display device 360 to display the estimated distance. The distance that the NOx sensor 290 can travel before reaching the end of its life can be obtained by creating a map in which the degradation level and the distance that can be traveled are associated with each other by, for example, experiments or simulations. In this way, the vehicle driver or the like can recognize that the replacement timing of the NOx sensor 290 is approaching, and perform planned maintenance before the end of the service life, for example, according to the distance that can be traveled. Can do. Then, by performing planned maintenance or the like, the NOx sensor 290 is prevented from suddenly failing, and the operating rate of the vehicle can be improved.

In step 4, the processor A of the control unit 340 pauses the NOx sensor 290. Here, when the NOx sensor 290 is paused, the built-in heater is also paused in order to suppress the progress of the deterioration level during the pause.

In step 5, the processor A of the control unit 340 refers to, for example, a map in which the NOx concentration according to the rotational speed and the load of the diesel engine 100 is set, and estimates the NOx concentration according to the rotational speed Ne and the load Q. . The processor A of the control unit 340 executes various controls based on the estimated NOx concentration instead of the output value of the NOx sensor 290. When the control unit 340 only manages the NOx sensor 290, the processor A of the control unit 340 outputs, for example, the estimated NOx concentration to the engine control unit that electronically controls the diesel engine 100. You can also.

In step 6, the processor A of the control unit 340 determines whether or not the temperature of the concentration detector 292A of the NOx sensor 290, that is, the sensor temperature Ts is higher than a predetermined temperature Tc. Here, the predetermined temperature Tc is used to determine whether or not the NOx sensor 290 receives heat from the exhaust and the temperature of the concentration detection unit 292A rises and the deterioration level may progress. The threshold value can be determined in consideration of the heat resistance performance of the NOx sensor 290, for example. If the processor A of the control unit 340 determines that the sensor temperature Ts is higher than the predetermined temperature Tc (Yes), the process proceeds to step 7. On the other hand, if the processor A of the control unit 340 determines that the sensor temperature Ts is equal to or lower than the predetermined temperature Tc (No), the process proceeds to step 8.

In step 7, the processor A of the control unit 340 operates the Peltier element 292D to cool the concentration detection unit 292A of the NOx sensor 290. At this time, if the processor A of the control unit 340 operates the Peltier element 292D so that the sensor temperature Ts becomes lower than the exhaust temperature T, the thermal degradation can be effectively delayed. Further, since the Peltier element 292D operates when the sensor temperature Ts is higher than the predetermined temperature Tc, the power consumed by the Peltier element 292D can be suppressed.

In Step 8, it is determined whether or not the processor A of the control unit 340 has stopped the NOx sensor 290 for a predetermined time. Here, the predetermined time defines the time during which the NOx sensor 290 is paused, and can be changed according to the deterioration level of the NOx sensor 290, for example. Specifically, the predetermined time can take a value that gradually increases as the deterioration level of the NOx sensor 290 progresses. If the processor A of the control unit 340 determines that the NOx sensor 290 is paused for a predetermined time (Yes), the process proceeds to step 9. On the other hand, if the processor A of the control unit 340 determines that the NOx sensor 290 is not paused for a predetermined time (No), the process returns to step 5.

In step 9, the processor A of the control unit 340 operates the NOx sensor 290. Since the NOx sensor 290 requires a certain amount of time until the concentration detection unit 292A is activated, the processor A of the control unit 340 uses or outputs the estimated NOx concentration until the concentration detection unit 292A is activated. You may do it.

FIG. 6 shows an example of a subroutine for diagnosing the deterioration level of the NOx sensor 290.
In step 11, the processor A of the control unit 340 reads the NOx concentration from the NOx sensor 290.

In step 12, the processor A of the control unit 340 refers to, for example, a map in which the NOx concentration according to the rotational speed and load of the diesel engine 100 is set, and estimates the NOx concentration according to the rotational speed Ne and the load Q. . Here, the NOx concentration set in the map can be a value in a state where the NOx sensor 290 has not deteriorated at all in order to represent standard data.

In step 13, the processor A of the control unit 340 compares the NOx concentration read in step 11 with the NOx concentration estimated in step 12, specifically, obtains a deviation between the two NOx concentrations. Here, since the NOx concentration estimated in step 12 is standard data, the deviation between the two NOx concentrations objectively represents the deterioration level with a number.

According to the sensor management process, the processor A of the control unit 340 determines the deterioration level of the NOx sensor 290 based on the comparison between the NOx concentration detected by the NOx sensor 290 and the NOx concentration estimated based on the engine operating state. Diagnose. Here, the NOx concentration estimated based on the engine operating state is a standard NOx concentration based on the NOx sensor 290 in which no deterioration has occurred. Therefore, this and the NOx concentration detected by the NOx sensor 290 The deviation of is an objective representation of the deterioration level numerically. For this reason, before the NOx sensor 290 reaches the end of its life, the deterioration level of the concentration detection unit 292A can be grasped.

The deterioration level of the NOx sensor 290 can be diagnosed by comparing the output signal of the first NOx sensor 290 and the output signal of the second NOx sensor 300, for example. However, when the deterioration levels of the first NOx sensor 290 and the second NOx sensor 300 progress simultaneously, the difference in the output signals of the sensors is small and it is difficult to diagnose the deterioration level. Therefore, if the estimated value of NOx concentration is compared with the actual measurement value, the deterioration level can be diagnosed independently for each NOx sensor 290. At this time, since the estimated value of the NOx concentration is an estimated value in the standard state, it varies according to the intake humidity. Therefore, in order to improve the estimation accuracy of the NOx concentration, the estimated value of the NOx concentration can be corrected based on the intake humidity H detected by the humidity sensor 330. The correction value for correcting the estimated value of the NOx concentration can be obtained through experiments, simulations, and the like, for example.

If the deterioration level of the NOx sensor 290 reaches the predetermined level Ld, the processor A of the control unit 340 operates the alarm 350 and the replacement timing of the NOx sensor 290 is approaching the driver of the vehicle. Is notified. For this reason, the driver of the vehicle can recognize that the replacement time of the NOx sensor 290 is approaching. At this time, in addition to the NOx sensor 290, the driver of the vehicle can also check whether there is an abnormality in other parts. This is because it may be diagnosed that the replacement time of the NOx sensor 290 is approaching due to an abnormality of other parts.

The processor A of the control unit 340 estimates the distance that the NOx sensor 290 can travel before reaching the end of its life based on the deterioration level of the NOx sensor 290, and displays this on the monitor 360. For this reason, the driver of a vehicle etc. can perform planned maintenance before the NOx sensor 290 reaches the end of its life, for example, based on the distance displayed on the monitor 360.

Further, when the deterioration level of the NOx sensor 290 reaches the predetermined level Ld, the processor A of the control unit 340 pauses the NOx sensor 290 for a predetermined time in order to suppress thermal deterioration of the NOx sensor 290. When the NOx sensor 290 is paused, the concentration detector 292A is not heated by the heater, so that the time integral of the sensor temperature is reduced and the progress of thermal degradation of the NOx sensor 290 can be delayed. That is, the detection accuracy of the NOx sensor 290 gradually decreases as the elapsed time increases as shown in FIG. However, by stopping the NOx sensor 290, as shown in FIG. 8, the decrease in detection accuracy during the pause is moderated, and the deterioration level after a predetermined time has elapsed from A to B (A> B). The life of the NOx sensor 290 can be extended.

In this way, when notifying the driver of the vehicle that the replacement timing of the NOx sensor 290 is approaching, processing for delaying the progress of the deterioration level of the NOx sensor 290 is executed. For this reason, it is suppressed that NOx sensor 290 becomes a lifetime within a guarantee period, for example, it can avoid making a vehicle user spend an unexpected repair expense.

At this time, since the NOx sensor 290 cannot detect the NOx concentration, the processor A of the control unit 340 estimates the NOx concentration based on the engine operating state, and executes various controls using the estimated NOx concentration. Therefore, even if the NOx sensor 290 is suspended, the influence on various controls can be suppressed. Note that the estimated value of the NOx concentration can be corrected based on the intake air humidity H.

Here, since the estimated value of the NOx concentration is obtained from a standard model in a steady state, for example, there is a characteristic that the estimation accuracy in a transient state such as during acceleration is not good. On the other hand, although the detection accuracy of the NOx sensor 290 gradually decreases due to deterioration or the like, it cannot follow the change in the transient state and cannot be omitted.

The predetermined time during which the NOx sensor 290 is paused can be changed according to the progress of thermal deterioration of the NOx sensor 290. That is, the deterioration level of the NOx sensor 290 is closely related to the time until the life of the NOx sensor 290. Therefore, by gradually increasing the predetermined time as the deterioration level progresses, the time until the NOx sensor 290 reaches the life is reached. The time can be extended.

Further, when the sensor temperature of the concentration detection unit 292A becomes higher than the predetermined temperature Tc when the NOx sensor 290 is paused, the processor A of the control unit 340 operates the Peltier element 292D to cool the concentration detection unit 292D. The thermal deterioration of the concentration detection unit 292A has a correlation with the time integral value of the sensor temperature. For this reason, it is possible to further suppress thermal degradation by cooling the concentration detector 292A, and as shown in FIG. 9, the degradation level after a predetermined time elapses decreases from B to C (B> C), and the NOx sensor 290 It is possible to further extend the time until the end of the service life. At this time, the processor A of the control unit 340 can effectively extend the life of the NOx sensor 290 by making the sensor temperature lower than the exhaust temperature T.

When the NOx sensor 290 is paused for a predetermined time, the processor A of the control unit 340 restarts the operation of the NOx sensor 290.

The processor A of the control unit 340 promotes activation of the concentration detection unit 292A of the NOx sensor 290 by changing the polarity of the voltage applied to the Peltier element 292D when the sensor temperature Ts has not reached the activation temperature. be able to. At this time, the concentration detector 292A of the NOx sensor 290 is heated by exhaust heat through the cover 292B and the Peltier element 292D in addition to the heating by the heater, so that it can be activated in a short time to detect the NOx concentration. .

Further, the processor A of the control unit 340 maintains the concentration detection unit 292A of the NOx sensor 290 in a predetermined temperature range by appropriately changing the polarity of the voltage applied to the Peltier element 292D according to the sensor temperature Ts, for example. Can do. In this way, the output signal of the NOx sensor 290 having temperature dependency can be stabilized, and the detection accuracy can be improved.

By the way, the DPF 194 of the continuous regeneration type DPF device 190 is continuously regenerated using the NO ₂ generated by the DOC converter 192. However, if the exhaust temperature T is relatively low for a long time, the regeneration process of the DPF 194 is not sufficiently performed, the amount of accumulated PM increases, and clogging occurs. For example, fuel consumption decreases due to an increase in back pressure. End up. For this reason, when clogging occurs in the DPF 194, a forced regeneration process is executed in which the exhaust gas temperature is raised by a known means to forcibly incinerate the PM deposited on the DPF 194. Here, whether or not clogging has occurred in the DPF 194 can be determined, for example, based on whether or not the differential pressure between the upstream side and the downstream side of the DPF 194 has become a predetermined value or more.

During execution of the forced regeneration process of the DPF 194, PM burns, so that the exhaust temperature flowing into the first NOx sensor 290 and the second NOx sensor 300 rises to promote thermal degradation. For this reason, during the execution of the forced regeneration process, the first NOx 290 and the second NOx sensor 300 can be paused to suppress thermal degradation. In this case, since the first NOx sensor 290 and the second NOx sensor 300 are exposed to high-temperature exhaust gas, the temperature can be lowered by operating the Peltier element 292D. In this way, the thermal deterioration of the concentration detection unit 292A progresses slowly, and its life can be extended.

Since the SCR converter 200 uses Fe or Ce having a low NOx purification rate in a low temperature range as an active species, the DOC converter 192 needs to carry many platinum group metals such as Pt (platinum) and Pd (palladium). . Therefore, it is conceivable to use an SCR converter 200 using Cu (copper) as an active species, which has an excellent NOx purification rate in a low temperature range. However, the SCR converter 200 using Cu as the active species has a lower NOx purification rate in the high temperature range than the SCR converter 200 using Fe or Ce as the active species. Therefore, it is necessary to increase the EGR rate of the diesel engine 100 to reduce the NOx emission amount. However, since the PM emission amount increases, the progress of clogging of the DPF 194 is accelerated.

Therefore, as a DPF 194, instead of a general cordierite base, as shown in FIG. 10, the ratio of the inflow area and the outflow area is asymmetric, specifically, the inflow area is larger than the outflow area. The use of silicon carbide (SiC) -based or aluminum titanate (Al ₂ TiO ₅ ) -based counteracts clogging progress.

The engine system is not limited to the diesel engine 100, and a gasoline engine or the like can also be used. Further, the exhaust sensor is not limited to the NOx sensor 290, but may be a sensor that detects one state quantity of the exhaust property of the engine, such as an O ₂ sensor or an air-fuel ratio sensor.

100 diesel engine (engine)
180 Exhaust passage 194 DPF
290 1st NOx sensor

292A Concentration detector

292D Peltier element 300 2nd NOx sensor 310 Rotational speed sensor 320 Load sensor 330 Humidity sensor 340 Control unit 350 Alarm 360 Monitor

Claims

An exhaust sensor for detecting one state quantity of engine exhaust properties;
A control unit with a built-in microcomputer;
Have
The control unit estimates one of the exhaust properties of the engine based on the operating state of the engine, and based on a comparison between the detected state quantity and the estimated state quantity, Diagnose the deterioration level,
An exhaust sensor management device.
The control unit corrects the estimated state quantity based on intake air humidity;
The exhaust sensor management device according to claim 1.
When the deterioration level of the exhaust sensor reaches a predetermined level, the control unit activates a notification device that notifies that effect,
The exhaust sensor management device according to claim 1 or 2,
When the deterioration level of the exhaust sensor reaches a predetermined level, the control unit estimates a distance that the exhaust sensor can travel before reaching the end of its life, and displays the estimated distance on a monitor.
The exhaust sensor management device according to any one of claims 1 to 3, characterized in that:
When the deterioration level of the exhaust sensor reaches a predetermined level, the control unit pauses the exhaust sensor and uses a state quantity estimated based on an operating state of the engine as an output value of the exhaust sensor. ,
The exhaust sensor management device according to any one of claims 1 to 4, wherein
The control unit pauses the exhaust sensor for a predetermined time;
The exhaust sensor management device according to claim 5.
The control unit changes the predetermined time according to a deterioration level of the exhaust sensor;
The exhaust sensor management device according to claim 6.
The predetermined time gradually increases as the deterioration level of the exhaust sensor advances.
The exhaust sensor management device according to claim 7.
When the control unit pauses the exhaust sensor, it activates a thermoelectric conversion element provided in a state quantity detection unit of the exhaust sensor to cool the detection unit.
The exhaust sensor management device according to any one of claims 5 to 8, wherein
The control unit operates the thermoelectric conversion element when the temperature of the detection unit exceeds a predetermined temperature;
The exhaust sensor management apparatus according to claim 9.
The control unit heats the detection unit by changing the polarity of the voltage applied to the thermoelectric conversion element when the temperature of the detection unit does not reach the activation temperature.
11. The exhaust sensor management apparatus according to claim 9 or 10,
The control unit pauses the exhaust sensor when the diesel particulate filter disposed in the exhaust passage of the engine is in the forced regeneration process;
The exhaust sensor management apparatus according to any one of claims 1 to 11, wherein the exhaust sensor management apparatus includes:
When the control unit pauses the exhaust sensor, the detection unit is cooled by causing a thermoelectric conversion element provided in the detection unit of the state quantity of the exhaust sensor;
The exhaust sensor management device according to claim 12.
A control unit that can read the output signal of the exhaust sensor that detects one state quantity of engine exhaust properties,
Based on the operating state of the engine, one state quantity of the exhaust property of the engine is estimated,
Diagnosing the deterioration level of the exhaust sensor based on a comparison between the state quantity read from the exhaust sensor and the estimated state quantity;
A method for managing an exhaust sensor.
The control unit corrects the estimated state quantity based on intake air humidity.
The exhaust sensor management method according to claim 14.