JP6191355B2 - Diagnostic equipment - Google Patents

Description

  The present invention relates to a diagnostic device, and more particularly, to a deterioration diagnosis of an exhaust purification catalyst provided in an exhaust system of an internal combustion engine.

  As an exhaust purification catalyst for exhaust systems such as diesel engines, an oxidation catalyst (Diesel Oxidation Catalyst: DOC) that oxidizes hydrocarbons (HC), carbon monoxide (CO), and nitric oxide (NO) contained in the exhaust. It has been known. Further, a diesel particulate filter (DPF) that collects particulate matter (PM) contained in exhaust gas is also known.

  When the HC oxidizing ability of the DOC deteriorates, a part of the HC supplied to the DOC by in-pipe injection or the like during the forced regeneration of the DPF is slipped to the downstream DPF without being oxidized. Since DPF also has HC oxidizing ability, HC slipped from DOC can be oxidized and purified by DPF. However, if the HC oxidation performance of the DPF also deteriorates, unburned HC slipped from the DOC may pass through the DPF and be released to the atmosphere, leading to a deterioration in emissions. Therefore, there is a request for diagnosing the HC oxidation ability of DOC and DPF in an on-board state (for example, see Patent Document 1).

JP 2003-106140 A

  As a method for diagnosing the HC oxidation performance, there is a technique in which exhaust temperature sensors are provided on the upstream side and downstream side of the DOC and DPF, and a diagnosis is made based on the HC heat generation amount estimated from the detection values of these exhaust temperature sensors. However, since DOC and DPF are accommodated in an exhaust pipe (catalyst case) disposed at the lower part of the vehicle body, the oxidization heat of HC is influenced by running wind and a part of it is radiated to the outside air. That is, the diagnosis method based only on the detection value of the exhaust temperature sensor does not take into account the amount of heat loss to the outside air, and therefore there is a possibility that highly accurate diagnosis cannot be performed.

  An object of the present invention is to provide a diagnostic apparatus that can perform a deterioration diagnosis of a catalytic function of a DPF with high accuracy.

  In order to achieve the above-described object, an internal combustion engine diagnostic apparatus according to the present invention includes an oxidation catalyst that is provided in an exhaust system of an internal combustion engine and oxidizes at least hydrocarbons contained in the exhaust, and an exhaust downstream side of the oxidation catalyst. A filter for collecting particulate matter contained in the exhaust, a supply means capable of supplying hydrocarbons to the oxidation catalyst, and at least an inlet exhaust temperature, an outlet exhaust temperature, an outside air temperature of the oxidation catalyst, and A first heat generation rate calculation means for calculating a hydrocarbon heat generation rate in the oxidation catalyst in consideration of a heat loss amount to the outside air based on a hydrocarbon supply amount supplied from the supply means; A slip amount calculating means for calculating an unburned hydrocarbon slip amount passing through the oxidation catalyst based on a hydrocarbon heat generation rate in the oxidation catalyst and the hydrocarbon supply amount; and at least an input of the filter Second heat generation rate calculation means for calculating a hydrocarbon heat generation rate in the filter in consideration of a heat loss amount to the outside air based on the exhaust temperature, the outlet exhaust temperature, the outside air temperature, and the calculated hydrocarbon slip amount And determination means for determining deterioration of the filter based on the calculated hydrocarbon heat generation rate in the filter.

  The first and second heat generation rate calculation means calculate the heat loss amount based on a first model expression including a natural convection heat transfer coefficient and a second model expression including a forced convection heat transfer coefficient. It is preferable.

  Further, the oxidation catalyst and the filter are accommodated in a cylindrical catalyst case provided in a lower part of a vehicle body, and the heat transfer coefficient of the forced convection is a turbulent flow on a flat plate that affects the forced convection on the lower surface of the catalyst case. It is preferable to set the number based on the assumed Nusselt number.

  The determination means may further determine the deterioration of the oxidation catalyst based on the calculated hydrocarbon heat generation rate in the oxidation catalyst.

  According to the diagnostic device of the present invention, the deterioration diagnosis of the catalytic function of the DPF can be performed with high accuracy.

1 is a schematic overall configuration diagram showing an intake / exhaust system of an engine to which a diagnostic device according to an embodiment of the present invention is applied. It is a schematic diagram explaining the energy preservation | save by oxidation of HC supplied to DOC, and oxidation of HC slipped from DOC to DPF. It is a typical side view explaining the heat loss of DOC and DPF by the influence of forced convection. It is the figure which compared HC oxidation ability (HC purification | cleaning performance) of normal DOC and degraded DOC. It is a flowchart which shows the control content by the diagnostic apparatus of this embodiment.

  Hereinafter, based on an accompanying drawing, a diagnostic device concerning one embodiment of the present invention is explained. The same parts are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  As shown in FIG. 1, a diesel engine (hereinafter simply referred to as an engine) 10 is provided with an intake manifold 10a and an exhaust manifold 10b. An intake passage 11 for introducing fresh air is connected to the intake manifold 10a, and an exhaust passage 12 for releasing exhaust gas to the atmosphere is connected to the exhaust manifold 10b.

  In the intake passage 11, an air cleaner 30, a MAF sensor 31, a turbocharger compressor 32a, and an intercooler 33 are provided in this order from the intake upstream side. In the exhaust passage 12, a turbocharger turbine 32b, a pre-stage post-treatment device 14, and a post-stage post-treatment device 20 are provided in order from the exhaust upstream side. In FIG. 1, reference numeral 36 denotes an outside air temperature sensor.

  The pre-stage post-treatment device 14 is configured by arranging a DOC 15 and a DPF 16 in order from the exhaust upstream side in a cylindrical catalyst case 14a. Further, the exhaust pipe injection device 13 is upstream of the DOC 15, the DOC inlet temperature sensor 17 is upstream of the DOC 15, the DOC outlet temperature sensor 18 is between the DOC 15 and the DPF 16, and the DPF outlet temperature sensor is downstream of the DPF 16. 19 are provided. Further, a differential pressure sensor 37 that detects a differential pressure between the upstream side and the downstream side of the DPF 16 is provided before and after the DPF 16.

  The exhaust pipe injection device 13 injects unburned fuel (mainly HC) into the exhaust passage 12 in response to an instruction signal output from an electronic control unit (hereinafter, ECU) 40. In addition, when using the post injection by the multistage injection of the engine 10, this in-pipe injection device 13 may be omitted.

The DOC 15 is formed, for example, by supporting a catalyst component on the surface of a ceramic carrier such as a cordierite honeycomb structure. When HC is supplied by the in-pipe injection device 13 or post injection, the DOC 15 oxidizes this and raises the exhaust temperature. Further, the DOC 15 generates NO ₂ by oxidizing NO in the exhaust gas, thereby increasing the ratio of NO ₂ to NO in the exhaust gas.

  The DPF 16 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the flow direction of the exhaust gas and alternately plugging the upstream side and the downstream side of these cells. The DPF 16 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and when the amount of accumulated PM reaches a predetermined amount, so-called forced regeneration is performed to remove the PM. The forced regeneration is performed by supplying unburned fuel (HC) to the DOC 15 by the exhaust pipe injection device 13 or post injection, and increasing the exhaust temperature flowing into the DPF 16 to the PM combustion temperature (for example, about 600 ° C.). . Further, the DPF 16 has an ability to oxidize unburned HC slipped without being oxidized by the upstream DOC 15.

  The DOC inlet temperature sensor 17 detects an upstream exhaust temperature (hereinafter referred to as a DOC inlet exhaust temperature) flowing into the DOC 15. The DOC outlet temperature sensor 18 detects the downstream exhaust temperature flowing out of the DOC 15 (hereinafter referred to as DOC outlet exhaust temperature or DPF inlet exhaust temperature). The DPF outlet temperature sensor 19 detects the downstream exhaust temperature flowing out from the DPF 16 (hereinafter referred to as the DPF outlet exhaust temperature). The detection values of these temperature sensors 17 to 19 are output to the electrically connected ECU 40.

  The post-stage post-treatment device 20 includes a urea water injection device 21 and an SCR 22 arranged in a cylindrical case 20a in order from the exhaust upstream side. An SCR inlet temperature sensor 23 is provided on the upstream side of the SCR 22.

The urea water injection device 21 injects urea water in a urea water tank (not shown) into the exhaust passage 12 between the pre-stage post-treatment device 14 and the post-stage post-treatment device 20 in response to an instruction signal output from the ECU 40. To do. The injected urea water is hydrolyzed by exhaust heat to generate NH ₃ and is supplied as a reducing agent to the downstream SCR 22.

The SCR 22 is formed, for example, by supporting iron zeolite on the surface of a ceramic carrier such as a honeycomb structure. The SCR 22 adsorbs NH ₃ supplied as a reducing agent and reduces and purifies NOx from the exhaust gas passing through the adsorbed NH ₃ .

  The ECU 40 performs various controls of the engine 10, the exhaust pipe injection device 13, and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like. Further, the ECU 40 includes a DOC heat generation rate calculation unit 41, a DOC deterioration determination unit 42, an HC slip amount calculation unit 43, a DPF heat generation rate calculation unit 44, and a DPF deterioration determination unit 45 as some functional elements. . Each of these functional elements will be described as being included in the ECU 40 which is an integral hardware, but any one of them can be provided in separate hardware.

The DOC heat generation rate calculation unit 41 is an example of the first heat generation rate calculation means of the present invention, and calculates the actual heat generation rate C _{DOC_act%} of HC oxidized by the DOC 15 during the forced regeneration of the DPF 16. Hereinafter, a detailed calculation procedure of the HC heat generation rate in the DOC 15 will be described.

As shown in FIG. 2, the actual heating value C _{DOC_act} of supplied from the exhaust pipe injector 13 during forced regeneration in DOC15 HC is exhausted between the upstream side of the exhaust energy Q _{DOC_in} and downstream exhaust energy Q _{DOC_out} of DOC15 It is obtained by adding the amount of heat loss Q _{DOC_lost} released from the DOC 15 to the outside air to the energy difference.

The upstream exhaust energy Q _{DOC_in} is calculated based on Equation 1 below, and the downstream exhaust energy Q _{DOC_out} is calculated based on Equation 2 below.

In Expressions 1 and 2, c _exh represents exhaust specific heat. Further, m _exh is the exhaust gas flow rate, and is obtained from the detection value of the MAF sensor 31, the fuel injection amount of the engine 10, and the like. The exhaust flow rate m _exh may be obtained directly from an exhaust flow sensor (not shown) or the like. T _{DOC_in} is the DOC inlet exhaust temperature, and is acquired by the DOC inlet temperature sensor 17. T _{DOC_out} is the DOC outlet exhaust temperature, and is acquired by the DOC outlet temperature sensor 18.

Heat loss quantity Q _{DOC_lost} can assume the heat loss quantity Q _{DOC_natural} by natural convection, the sum of the heat loss quantity Q _{DOC_forced} by forced convection and _{(Q DOC_lost = Q DOC_natural + Q} DOC_forced).

The heat loss amount Q _{DOC_natural} due to natural convection is calculated based on the following Equation 3.

In Equation 3, A _{s_DOC} indicates an effective area of the outer peripheral surface of the DOC 15 (or the outer peripheral surface of the portion where the DOC 15 of the catalyst case 14a is provided). T _{DOC_brick} is the internal temperature of the DOC ₁₅ and is obtained as an average value of the DOC inlet exhaust temperature T _{DOC_in} and the DOC outlet exhaust temperature T _{DOC_out} . T _ambient is the outside air temperature and is acquired by the outside air temperature sensor 36. h _{n_DOC} is the heat transfer coefficient of natural convection and is obtained from the following Equation 4.

In Equation 4, k represents the thermal conductivity of air. L _{n_DOC} is the representative length of the DOC _{15 and} is appropriately set according to the capacity of the DOC 15 and the like. Nu _{n_DOC} indicates the Nusselt number of natural convection.

Generally, the DOC 15 has a columnar shape, and the catalyst case 14a that accommodates the DOC 15 is formed in a substantially cylindrical shape. Therefore, it is considered that the oxidation heat generated in the DOC 15 is dissipated to the outside air through the entire surface of the cylindrical outer peripheral surface of the DOC 15 and the catalyst case 14a. Assuming that the heat radiation by natural convection is transmitted from the entire surface of the outer peripheral surface of the cylinder with the axis oriented in the horizontal direction, the Nusselt number Nu _{n_DOC} can be obtained from the following Equation 5 where the glassphos number is Gr and the Prandtl number is Pr.

The heat loss amount Q _{DOC_forced} due to forced convection is calculated based on the following Equation 6.

In Formula 6, A _{f_DOC} indicates an effective area of the outer peripheral surface of the DOC 15 (or the outer peripheral surface of the portion where the DOC 15 of the catalyst case 14a is provided). h _{f_DOC} is a heat transfer coefficient of forced convection and is obtained from Equation 7 below.

In Expression 7, L _{f_DOC} is a representative length of the DOC _{15 and} is appropriately set according to the capacity of the DOC 15 and the like. Nu _{f_DOC} represents the Nusselt number of forced convection.

As shown in FIG. 3, generally, the catalyst case 14a accommodating the DOC 15 is fixed to the lower part of the chassis frame S of the vehicle body, and a transmission TM or the like is disposed in front thereof. Therefore, it can be assumed that the traveling wind flowing from the front of the vehicle body to the lower part during traveling is a turbulent flow on a flat plate that affects only the lower surface of the DOC 15 (or the catalyst case 14a). That is, the forced convection Nusselt number Nu _{f — DOC} is obtained from the following Equation 8 derived by solving a turbulent heat transfer equation on a flat plate.

In Equation 8, Re represents the Reynolds number. The Reynolds number Re is obtained from Equation 9 below, where the average velocity of air is v, the air density is ρ, the representative length of DOC 15 is L _{f_DOC} , and the kinematic viscosity coefficient is μ.

The DOC heat generation rate calculation unit 41 calculates the difference in the exhaust energy between the upstream exhaust energy Q _{DOC_in} calculated based on the above-described equation 1 and the downstream exhaust energy Q _{DOC_out} calculated based on the above-described equation 2. By adding the heat loss amount Q _{DOC_lost} calculated based on Equations 3 to 9, the HC actual heat generation amount C _{DOC_act} in the DOC 15 at the time of forced regeneration is calculated. Then, by dividing the HC actual heating value C _{DOC_act} theoretical calorific C _{DOC_theo} exhaust pipe injection (or post injection), and is configured to calculate the HC actual heat rate C _{DOC_act%} of within DOC15 ( _{CDOC_act%} = _{CDOC_act} / _{CDOC_theo} ). The theoretical heat generation amount C _{DOC_theo} is obtained by multiplying the exhaust pipe injection amount (or post injection amount) HC _{inj_qty} by the HC theoretical heat generation rate C _theo% (C _{DOC_theo} = HC _{inj_qty} · C _theo% ).

The DOC deterioration determination unit 42 is an example of a determination unit according to the present invention, and determines the deterioration state of the DOC 15 based on the HC actual heat generation rate C _{DOC_ACT%} calculated by the HC heat generation rate calculation unit 41. More specifically, the ECU 40 stores an HC heat generation rate threshold value C _{DOC_STD%} obtained when a predetermined amount of HC is almost completely oxidized in the DOC 15 and obtained in advance through experiments or the like. When the difference ΔC _{DOC_%} between the HC heat generation rate threshold C _{DOC_STD%} and the HC actual heat generation rate C _{DOC_ACT%} reaches a predetermined upper limit threshold ΔC _MAX indicating the deterioration of the DOC ₁₅ , the DOC deterioration determination unit 42 HC purification performance) is determined as a deteriorated state. Note that the state in which the HC purification performance of the DOC 15 has deteriorated is different from the normal HC purification rate due to, for example, aging degradation or breakage as shown in FIG. 4 (the catalyst activation temperature is shifted to the high temperature side). State).

The HC slip amount calculation unit 43 is an example of the slip amount calculation means of the present invention, and the HC actual heat generation rate C _{DOC_ACT%} calculated by the HC heat generation rate calculation unit 41 and the exhaust pipe injection amount (or post injection amount). Based on HC _{inj_qty} , the slip amount HC _{slp_qty} of unburned HC flowing into the downstream DPF 16 without being oxidized by the _{DOC 15} is calculated. The slip amount HC _{slp_qty} is obtained by multiplying the exhaust pipe injection amount HC _{inj_qty} by the HC actual heat generation rate C _{DOC_ACT%} (HC _{slp_qty} = HC _{inj_qty} × (1−C _{DOC_ACT%} )).

The DPF heat generation rate calculation unit 44 is an example of the second heat generation rate calculation means of the present invention, and calculates the actual heat generation rate C _{DPF_act%} of HC that slips through the DOC 15 and flows into the DPF 16 during forced regeneration. Hereinafter, a detailed calculation procedure of the HC heat generation rate in the DPF 16 will be described.

As shown in FIG. 2, the actual heating value C _{DPF_act} of HC to be oxidized by the DPF 16 to slip DOC15 is the exhaust energy difference between the exhaust energy Q _{DPF_out} the upstream side of the exhaust energy Q _{DPF_in} and downstream of the DPF 16, It is obtained by adding the amount of heat loss Q _{DPF_lost} released from the DPF 16 to the outside air.

The upstream exhaust energy Q _{DPF_in} is calculated based on Equation 10 below, and the downstream exhaust energy Q _{DPF_out} is calculated based on Equation 11 below.

In Expressions 10 and 11, T _{DPF_in} is the DPF inlet exhaust temperature, and is acquired by the DOC outlet temperature sensor 18. T _{DPF_out} is the DPF outlet exhaust temperature, and is acquired by the DPF outlet temperature sensor 19. The DPF outlet exhaust temperature _{TDPF_out} may be acquired by the SCR inlet temperature sensor 23.

Heat loss quantity Q _{DPF_lost} can assume the heat loss quantity Q _{DPF_natural} by natural convection, the sum of the heat loss quantity Q _{DPF_forced} by forced convection and _{(Q DPF_lost = Q DPF_natural + Q} DPF_forced).

The amount of heat loss Q _{DPF_natural} due to natural convection is calculated based on Equation 12 below.

In Equation 12, A _{s_DPF} represents the effective area of the outer peripheral surface of the DPF 16 (or the outer peripheral surface of the portion of the catalyst case 14a where the DPF 16 is provided). T _{DPF_brick} is the internal temperature of the DPF 16 and is obtained as an average value of the DPF inlet exhaust temperature T _{DPF_in} and the DPF outlet exhaust temperature T _{DPF_out} . h _{n_DPF} is a natural convection heat transfer coefficient, and is obtained from the following Equation 13.

In Expression 13, L _{n_DPF} is a representative length of the DPF 16 and is appropriately set according to the capacity of the DPF 16 and the like. Nu _{n_DPF} is the natural convection Nusselt number, and can be obtained from the following equation 14 assuming that heat is _radiated from the entire cylindrical outer peripheral surface of the DPF 16 and the catalyst case 14a as in the above equation 5.

The heat loss amount Q _{DPF_forced} due to forced convection is calculated based on the following Equation 15.

In Formula 15, A _{f_DPF} indicates the effective area of the outer peripheral surface of the DPF 16 (or the outer peripheral surface of the portion where the DPF 16 of the catalyst case 14a is provided). h _{f_DPF} is a heat transfer coefficient of forced convection and is obtained from the following equation (16).

In Expression 16, L _{f_DPF} is a representative length of the DPF 16 and is appropriately set according to the capacity of the DPF 16 and the like. Nu _{f_DPF} is the Nusselt number of forced convection, and assuming that the forced convection is a turbulent flow on a flat plate that affects only the lower surface of the DPF 16 (or the catalyst case 14a), as in Equation 8 above, The following equation 17 can be obtained.

The Reynolds number Re in Equation 17 is obtained from Equation 18 below, where the average velocity of air is v, the air density is ρ, the representative length of DPF 16 is L _{f —} DPF, and the kinematic viscosity coefficient is μ.

DPF heating rate calculating section 44, the upstream side of the exhaust energy Q _{DPF_in} calculated based on Equation 10 above, the exhaust energy difference between the downstream side of the exhaust energy Q _{DPF_out} calculated based on Equation 11 above, above The HC actual heat generation amount C _{DPF_act} in the DPF 16 is calculated by adding the heat loss amount Q _{DPF_lost} calculated based on Equations 12-18. Then, by dividing the theoretical calorific value C _{DPF_theo} of HC that slip HC actual heating value C _{DPF_act} from DOC15, and is configured to calculate the HC actual heat rate C _{DPF_act%} of within DPF16 (C _{DPF_act%} = C _{DPF_act} / C _{DPF_theo} ). The theoretical heat generation amount C _{DPF_theo} is obtained by multiplying the slip amount HC _{slp_qty} by the theoretical heat generation rate C _theo% of HC (C _{DPF_theo} = C _{slp_qty} × C _theo% ).

The DPF deterioration determination unit 45 is an example of a determination unit of the present invention, and determines the deterioration state of the DPF 16 based on the HC actual heat generation amount _{CDPF_actT%} calculated by the DPF heat generation rate calculation unit 44. More specifically, the ECU 40 stores an HC heat generation rate threshold value _{CDPF_STD%} obtained in advance by experiments or the like when a predetermined amount of HC is almost completely oxidized in the DPF 16. When the difference ΔC _{DPF_%} between the HC heat generation rate threshold C _{DPF_STD%} and the HC actual heat generation rate C _{DPF_act%} reaches a predetermined upper limit threshold ΔC _MAX indicating the deterioration of the DPF 16, the DPF deterioration determination unit 45 HC purification performance) is determined as a deteriorated state.

  Next, based on FIG. 5, the control flow by the diagnostic apparatus of this embodiment is demonstrated.

In step (hereinafter, simply referred to as S) 100, for example, it is determined whether or not the PM deposition amount PM _depo deposited on the DPF 16 has reached the upper limit value PM _MAX based on the differential pressure across the DPF 16. . When the PM accumulation amount PM _depo reaches the upper limit value PM _MAX , the present control proceeds to S110.

  In S110, exhaust pipe injection (or post injection) by the exhaust pipe injection device 13 is started, and forced regeneration of the DPF 16 is executed.

In S120, the exhaust energy difference between the upstream side of the exhaust energy Q _{DOC_in} and downstream of the exhaust energy Q _{DOC_out,} by adding the heat loss Q _{DOC_lost} is radiated to the outside air, HC actual heating value C _{DOC_act} in DOC15 Is calculated. Further, in S130, by dividing the actual heating value C _{DOC_act} calculated in S120 by the theoretical calorific value C _{DOC_theo} exhaust pipe injection (or post injection), HC actual heat rate C _{DOC_act%} of within DOC15 is calculated . The theoretical heat generation amount C _{DOC_theo} is obtained by multiplying the exhaust pipe injection amount (or post injection amount) HC _{inj_qty} by the HC theoretical heat generation rate C _theo% .

In S140, the deterioration determination of the DOC 15 is performed by comparing the HC actual heat rate C _{DOC_act%} calculated in S130 with the HC heat rate threshold value C _{DOC_STD%} . When the difference ΔC _{DOC_%} between the HC heat generation rate threshold C _{DOC_STD%} and the HC actual heat generation rate C _{DOC_act%} has not reached the upper limit threshold ΔC _MAX (No), the HC oxidation performance of the DOC 15 is normal, so this control is S100. Returned to That is, the determination of the deterioration of the DOC 15 is suspended until the next forced regeneration. On the other hand, when the difference ΔC _{DOC_%} has reached the upper limit threshold ΔC _MAX (Yes), the HC oxidation capability (HC purification performance) of the DOC 15 is determined to be a deteriorated state in S150.

If it is determined that the DOC 15 is deteriorated in S150, the HC supplied to the DOC 15 during the forced regeneration slips to the DPF 16. Therefore, the present control proceeds to S160, and the slip amount HC _{slp_qty} is calculated. The slip amount HC _{slp_qty} is obtained by multiplying the exhaust pipe injection amount HC _{inj_qty} by the HC actual heat generation rate C _{DOC_ACT%} .

In S170, the HC actual heat generation amount C _{DPF_act} in the DPF 16 is added to the exhaust energy difference between the upstream exhaust energy Q _{DPF_in} and the downstream exhaust energy Q _{DPF_out} by the heat loss amount Q _{DPF_lost radiated} to the outside air. Is calculated. Furthermore, in S180, the HC actual heat generation rate C _{DPF_act%} in the DPF 16 is calculated by dividing the HC actual heat generation amount C _{DPF_act} calculated in S170 by the theoretical heat generation amount C _{DPF_theo} of HC slipped from the _DOC15 . The theoretical heat generation amount C _{DPF_theo} is obtained by multiplying the slip amount HC _{slp_qty} by the theoretical heat generation rate C _theo% of HC.

In S190, the deterioration determination of the DPF 16 is performed by comparing the HC actual heat generation rate C _{DPF_act%} calculated in S170 with the HC heat generation rate threshold C _{DPF_STD%} . When the difference ΔC _{DPF_%} between the HC heat generation rate threshold C _{DPF_STD%} and the HC actual heat generation rate C _{DPF_act%} does not reach the upper limit threshold ΔC _MAX (No), the HC oxidation performance of the DPF 16 is normal, so this control is performed in S100. Returned to On the other hand, when the difference ΔC _{DPF_%} has reached the upper limit threshold ΔC _MAX (Yes), it is determined in S200 that the HC oxidation capability (HC purification performance) of the DPF 16 is in a deteriorated state, and this control is thereafter returned.

  Next, functions and effects of the diagnostic apparatus according to the present embodiment will be described.

  In the diagnostic device of the present embodiment, the actual calorific value of HC supplied to the DOC 15 during forced regeneration is based on the exhaust energy difference between the upstream side and the downstream side of the DOC 15 and the amount of heat loss radiated from the DOC 15 to the outside air. Calculated. Further, the actual calorific value of HC slipped from the DOC 15 and oxidized by the DPF 16 is calculated based on the exhaust energy difference between the upstream side and the downstream side of the DPF 16 and the heat loss amount radiated from the DPF 16 to the outside air.

  That is, it is configured to calculate the HC heat generation amount of the DOC 15 and the DPF 16 with higher accuracy by considering the amount of heat loss to the outside air than the method of calculating the HC heat generation amount of the DOC 15 and the DPF 16 based only on the upstream and downstream exhaust temperature differences. ing. Therefore, according to the diagnostic apparatus of the present embodiment, it is possible to diagnose the deterioration of the HC oxidation ability of the DOC 15 and the DPF 16 with high accuracy.

  Further, in the diagnostic device of the present embodiment, the amount of heat loss to the outside air is calculated using model equations including the natural convection heat transfer coefficient (Equations 3 to 5, 12 to 14) and model expressions including the forced convection heat transfer coefficient. (Equation 6-9, 15-18) and the calculation. Of these, the heat transfer coefficient of natural convection is set from the Nusselt number assumed to radiate heat from the entire cylindrical outer peripheral surface of DOC15 or DPF16, and the heat transfer coefficient of forced convection affects the lower surface of DOC15 or DPF16. It is set from the Nusselt number assumed to be turbulent flow on a given flat plate.

  That is, the heat loss amount to the outside air is accurately calculated based on a model formula that takes into consideration the shape, arrangement position, influence of traveling wind, and the like of the DOC 15, the DPF 16, and the catalyst case 14a. Therefore, according to the diagnostic device of the present embodiment, it is possible to calculate an accurate HC actual heat generation amount taking into account the influence of the shape, arrangement, forced convection, and the like, and the diagnostic accuracy can be improved reliably.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

  For example, although the deterioration diagnosis has been described as being performed at the time of forced regeneration of the DPF 16, it may be performed at times other than forced regeneration. In this case, the exhaust pipe injection (or post injection) may be executed regardless of the PM accumulation amount of the DPF 16. Moreover, although the deterioration diagnosis of the DPF 16 has been described as being performed when the HC slips from the DOC 15, it may be configured to be performed even when the DOC 15 is not deteriorated. In this case, it is only necessary to intentionally slip the HC from the DOC 15 by increasing the injection amount of the exhaust pipe injection (or post injection). Further, the engine 10 is not limited to a diesel engine, and can be widely applied to other internal combustion engines such as a gasoline engine.

10 Engine 13 Exhaust pipe injection device (supply means)
15 DOC (oxidation catalyst)
16 DPF (filter)
40 ECU
41 DOC heat generation rate calculation unit (first heat generation amount estimation means)
42 DOC deterioration determination unit (determination means)
43 HC slip amount calculation unit (slip amount calculation means)
44 DPF heat generation rate calculation section (second heat generation amount estimation means)
45 DPF degradation determination unit (determination means)

Claims (3)

An oxidation catalyst provided in an exhaust system of an internal combustion engine for oxidizing at least hydrocarbons contained in the exhaust;
A filter provided on the exhaust downstream side of the oxidation catalyst for collecting particulate matter contained in the exhaust;
Supply means capable of supplying hydrocarbons to the oxidation catalyst;
Hydrocarbon heat generation in the oxidation catalyst taking into account the amount of heat loss to the outside air based on at least the inlet exhaust temperature, the outlet exhaust temperature, the outside air temperature of the oxidation catalyst, and the amount of hydrocarbons supplied from the supply means First heat rate calculating means for calculating a rate;
Slip amount calculating means for calculating the amount of unburned hydrocarbon slip passing through the oxidation catalyst based on the calculated hydrocarbon heat generation rate in the oxidation catalyst and the amount of hydrocarbon supply;
Calculating a hydrocarbon heat generation rate in the filter in consideration of an amount of heat loss to the outside air based on at least the inlet exhaust temperature, the outlet exhaust temperature, the outside air temperature, and the calculated amount of the hydrocarbon slip of the filter; 2 heating rate calculation means;
Determination means for determining deterioration of the filter based on the calculated hydrocarbon heat generation rate in the filter ,
The first and second heat generation rate calculating means calculates the amount of heat loss based on a first model formula including a heat transfer coefficient of natural convection and a second model expression including a heat transfer coefficient of forced convection,
The oxidation catalyst and the filter are accommodated in a cylindrical catalyst case provided at the lower part of the vehicle body,
The catalyst case is arranged so that the traveling wind flows below the axis center in the horizontal direction,
The diagnostic device according to claim 1, wherein the heat transfer coefficient of the forced convection is set based on a Nusselt number on the assumption that the forced convection is a turbulent flow on a flat plate that affects a lower surface of the catalyst case . A transmission is arranged in front of the catalyst case,
The diagnostic device according to claim 1, wherein the heat transfer coefficient of the forced convection is set based on a Nusselt number on the assumption that the forced convection is a turbulent flow on a flat plate that affects only a lower surface of the catalyst case . The determining means further computed on the basis of the hydrocarbon heat generation rate in the oxidation catalyst diagnosis apparatus according to claim 1 or 2 determines the deterioration of the oxidation catalyst.

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