JP2014177875A - Exhaust temperature estimation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust temperature estimation device capable of achieving a low-cost and accurate estimation of an exhaust temperature in an exhaust passage under a wide range of conditions.SOLUTION: An exhaust temperature estimation device has an oxidation catalyst (5) and a DPF (6) in an exhaust passage (4) of an internal combustion engine (1) and estimates an exhaust temperature in the exhaust passage at one side either upstream or downstream of the oxidation catalyst on the basis of a detection value of an exhaust temperature sensor (11) installed at the other side. The exhaust temperature estimation device can execute an accurate exhaust temperature estimation by using a thermal balance model taking into account an oxidation combustion heating value Qon the basis of an additive amount of hydrocarbon and a heat exchange amount Qbetween the oxidation catalyst and exhaust.

Description

  The present invention relates to a technical field of an exhaust gas temperature estimating device in which an oxidation catalyst and a DPF are provided in an exhaust gas passage of an internal combustion engine, and an exhaust gas temperature in the exhaust gas passage can be estimated.

In recent years, the reduction of air pollutants contained in exhaust gas from internal combustion engines such as diesel engines has become a major issue. Therefore, in the exhaust passage, oxygen contained in the exhaust is used to oxidize unburned substances, mainly hydrocarbons (HC) in the exhaust, and decompose them into water (H ₂ 0) and carbon dioxide (CO ₂ ). An exhaust aftertreatment device is provided that includes an oxidation catalyst (DOC) that performs the purification, a diesel particulate filter (DPF) that performs purification by collecting unburned fine substances (PM) in the exhaust gas, and the like. In this type of exhaust aftertreatment device, the purification capability decreases as the amount of PM accumulated in the DPF increases. Therefore, the regeneration processing is performed at a predetermined timing to perform the combustion treatment of the accumulated PM.

  In the exhaust aftertreatment device, temperature management is important for ensuring its performance. In particular, oxidation catalysts need to be heated to an activation temperature or higher so that sufficient purification ability can be exhibited. On the other hand, excessive temperature rise may cause deterioration or damage. There is. For this reason, exhaust temperature sensors are respectively installed before and after the oxidation catalyst provided in the exhaust passage. However, since this type of exhaust temperature sensor is relatively expensive, it is desired to reduce the number of installation locations from the viewpoint of cost reduction.

  As a measure for reducing the installation location of such exhaust temperature sensors, the number of sensors is reduced by estimating the exhaust temperature at other locations based on the detection value of the exhaust temperature sensor installed at a predetermined location. It is possible. Although Patent Documents 1 and 2 do not aim to reduce the number of exhaust temperature sensors, the exhaust temperature of the other is estimated based on the detected value of the exhaust temperature sensor installed in either of the exhaust passages before or after the oxidation catalyst. Techniques to do this are disclosed.

JP 2006-22730 A Japanese Patent No. 4325367

  In Patent Document 1, the exhaust gas temperature can be estimated only when the operating state of the internal combustion engine is in a predetermined stable state. Further, in Patent Document 2, it is possible to estimate the exhaust temperature only when a limited operating condition that can ignore the HC oxidation combustion heat in the oxidation catalyst is satisfied. Thus, in the prior art, the exhaust temperature can be estimated only when a very limited condition is satisfied (for example, it cannot be estimated during DPF regeneration or in a transient operating state), so during the operation of the internal combustion engine. It is not suitable for monitoring exhaust aftertreatment devices that are used regularly. Therefore, if the above technique is applied as it is, it is difficult to reduce the exhaust temperature sensor.

  In Patent Document 2, a series of systems including an oxidation catalyst is modeled in order to estimate the exhaust temperature. The delay of the exhaust temperature with respect to changes in operating conditions is expressed by a simple transfer function such as a first-order lag filter. Therefore, it is difficult to obtain good estimation accuracy.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an exhaust temperature estimation device capable of realizing the estimation of the exhaust temperature in the exhaust passage under a wide range of conditions at low cost and with high accuracy.

  In order to solve the above problems, an exhaust gas temperature estimation device according to the present invention is provided with an oxidation catalyst in an exhaust passage of an internal combustion engine and a DPF downstream of the oxidation catalyst, the upstream side of the oxidation catalyst in the exhaust passage, Or an exhaust gas temperature estimating device for estimating an exhaust gas temperature between one of the oxidation catalyst and the DPF, the upstream side of the oxidation catalyst in the exhaust passage, or the other between the oxidation catalyst and the DPF. Exhaust temperature detection means for detecting the first exhaust gas temperature, HC addition amount detection means for detecting the HC addition amount to the oxidation catalyst, and oxidation combustion heat quantity for calculating the oxidation combustion heat amount in the oxidation catalyst from the HC addition amount Calculating means, heat exchange amount calculating means for calculating a heat exchange amount between the oxidation catalyst and the exhaust gas flowing through the oxidation catalyst, the detected first exhaust temperature, and the oxidation fuel Based on the amount of heat and the heat exchange amount, characterized by comprising an exhaust temperature estimating means for estimating a second exhaust gas temperature in the said one.

According to the present invention, the heat balance model in the oxidation catalyst is constructed by calculating the oxidation combustion heat amount obtained from the HC addition amount by post injection or the like, and the heat exchange amount between the oxidation catalyst and the exhaust, From the exhaust temperature (the upstream side of the oxidation catalyst or the detected value of the exhaust temperature between the oxidation catalyst and the DPF) to the second exhaust temperature (the exhaust side upstream of the oxidation catalyst or the other side between the oxidation catalyst and the DPF) Temperature). Such estimation of the exhaust temperature can be performed under a wide range of conditions regardless of the operating state of the internal combustion engine. Therefore, it is possible to reduce the cost by eliminating the exhaust temperature detection means before or after the oxidation catalyst. it can.
Moreover, since such a heat balance model is closer to the substance compared to a case where a transfer function such as a first-order lag filter as in the prior art is used, a good estimation accuracy can be obtained.

In one aspect of the present invention, the apparatus includes an outside air temperature detecting unit that detects an outside air temperature, and a heat release amount calculating unit that calculates a heat release amount from the oxidation catalyst to the outside air from a temperature difference between the outside air and the oxidation catalyst. The heat exchange amount calculation means calculates the heat exchange amount based on the heat dissipation amount.
According to this aspect, the exhaust gas temperature can be estimated with higher accuracy by incorporating the heat release amount from the oxidation catalyst to the outside air in the heat balance model.

In another aspect, the oxidation combustion heat quantity calculating means obtains the maximum HC reaction amount that can be reacted with the oxidation catalyst using the Arrhenius rule with the oxidation catalyst temperature as a parameter, and the HC addition amount is the HC maximum reaction amount. When larger than the amount, the oxidation combustion heat is calculated with the HC maximum reaction amount as the HC addition amount.
According to this aspect, when an excessive amount of HC is added by post-injection or the like, the amount of HC maximum reaction amount (the amount of HC that can be reacted with the oxidation catalyst) is taken into consideration without flowing through the downstream side without reacting with the oxidation catalyst. By calculating the oxidation combustion heat based on the maximum value, the exhaust gas temperature can be estimated with higher accuracy.

In another aspect, the exhaust temperature detecting means detects an exhaust temperature between the oxidation catalyst and the DPF in the exhaust passage as the first exhaust temperature.
According to this aspect, the exhaust gas temperature upstream of the oxidation catalyst can be estimated by detecting the exhaust gas temperature between the oxidation catalyst and the DPF. By detecting the exhaust temperature between the oxidation catalyst and the DPF as the first exhaust temperature in this way, the exhaust temperature after passing through the oxidation catalyst can be monitored as an actual measurement value, so the exhaust temperature upstream of the oxidation catalyst is set to the first exhaust temperature. Compared to the case where the temperature is detected as a temperature, the actual state of the oxidation catalyst can be reliably grasped.

  When the exhaust gas temperature detecting means detects the exhaust gas temperature upstream of the oxidation catalyst in the exhaust gas passage as the first exhaust gas temperature, the exhaust gas temperature is detected by detecting the exhaust gas temperature upstream of the oxidation catalyst. The exhaust temperature between the catalyst and the DPF can be estimated. In this case, by detecting the exhaust gas temperature before passing through the oxidation catalyst, the detected value has a small time lag, and the exhaust gas temperature is more accurate than when the exhaust gas temperature between the oxidation catalyst and the DPF is detected as the first exhaust gas temperature. Can be estimated.

In another aspect, the exhaust temperature detecting means is provided between the oxidation catalyst and the DPF in the exhaust passage.
According to this aspect, by providing the exhaust gas temperature detecting means between the oxidation catalyst and the DPF, the exhaust gas temperature upstream of the oxidation catalyst can be estimated. By detecting the exhaust temperature between the oxidation catalyst and the DPF as the first exhaust temperature in this way, the exhaust temperature after passing through the oxidation catalyst can be monitored as an actual measurement value, so the exhaust temperature upstream of the oxidation catalyst is set to the first exhaust temperature. Compared to the case where the temperature is detected as a temperature, the actual state of the oxidation catalyst can be reliably grasped.

  When the exhaust temperature detecting means is provided on the upstream side of the oxidation catalyst, the exhaust temperature between the oxidation catalyst and the DPF can be estimated. In this case, by detecting the exhaust gas temperature before passing through the oxidation catalyst, the detected value has a small time lag, and the exhaust gas temperature can be estimated more accurately than when the exhaust gas temperature detection means is provided between the oxidation catalyst and the DPF. .

According to the present invention, the heat balance model in the oxidation catalyst is constructed by calculating the oxidation combustion heat amount obtained from the HC addition amount by post injection or the like, and the heat exchange amount between the oxidation catalyst and the exhaust, From the exhaust temperature (the upstream side of the oxidation catalyst or the detected value of the exhaust temperature between the oxidation catalyst and the DPF) to the second exhaust temperature (the exhaust side upstream of the oxidation catalyst or the other side between the oxidation catalyst and the DPF) Temperature). Such estimation of the exhaust temperature can be performed under a wide range of conditions regardless of the operating state of the internal combustion engine. Therefore, it is possible to reduce the cost by eliminating the exhaust temperature detection means before or after the oxidation catalyst. it can.
Moreover, since such a heat balance model is closer to the substance compared to a case where a transfer function such as a first-order lag filter as in the prior art is used, a good estimation accuracy can be obtained.

It is a block diagram which shows the internal structure of the vehicle carrying the exhaust temperature estimation apparatus which concerns on a present Example. It is a flowchart of exhaust temperature estimation control. It is a figure which shows notionally the control content of exhaust temperature estimation control.

  Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. This is just an example.

(overall structure)
FIG. 1 is a block diagram showing the internal structure of a vehicle equipped with an exhaust gas temperature estimating apparatus according to this embodiment.
Reference numeral 1 denotes a diesel engine (hereinafter referred to as “engine” where appropriate) that is an internal combustion engine equipped with a common rail fuel spray device. Fuel is directly injected into the combustion chamber of each cylinder from a fuel injection valve, and compression ignition is performed. Combustion takes place. The fuel injection timing and the injection amount of the fuel injection valve are electrically controlled by an electronic control unit (hereinafter referred to as “ECU” as appropriate) 10.

  Intake introduced from the outside through the air cleaner 2 is taken into the engine 1 through the intake pipe 3, and exhaust gas generated by compression ignition combustion in the combustion chamber is discharged to the exhaust pipe 4. The exhaust pipe 4 includes an oxidation catalyst (DOC) 5 and a diesel particulate filter (DPF) 6 in order from the upstream side.

In DOC5, oxygen contained in exhaust gas is used to oxidize unburned substances mainly composed of hydrocarbons (HC) in exhaust gas and decompose them into water (H ₂ 0) and carbon dioxide (CO ₂ ).
The DPF 6 performs purification by collecting unburned fine substances (PM) in the exhaust gas. As the accumulated amount of PM collected in the DPF 6 increases, the purification capability decreases, so that the regeneration process of the DPF 6 is performed at a predetermined timing. During the regeneration process, fuel (HC) is injected into the exhaust pipe 4 by the HC addition device 7 provided on the upstream side of the DOC 5, the fuel contained in the exhaust is oxidized by the DOC 5, and the temperature of the exhaust is increased. The accumulated exhaust gas is sent to the DPF 6 to burn the accumulated PM.

The exhaust gas purified by the DOC 5 and the DPF 6 in this way is converted into nitrogen (NOx) in the exhaust water (H ₂ 0) and nitrogen (N ₂ ) in a NOx selective reduction catalyst (not shown) arranged further downstream. ) And then discharged outside.

The intake pipe 3 is provided with an intake flow rate sensor 8 for detecting an intake flow rate G _air [kg / s]. The exhaust pipe 4 upstream of DOC5 pressure sensor 9 for detecting the inlet pressure _{P in} the DOC5 is provided. An exhaust temperature sensor 11 for detecting a downstream temperature T _out [K] of the DOC 5 is provided between the DOC 5 and the DPF 6 in the exhaust pipe 4. The vehicle is also provided with an outside air temperature sensor 12 for detecting the outside air temperature T _amb [K] and a vehicle speed sensor 13 for detecting the _vehicle speed V _vehicle [km / h].
Detection value G _air [kg / s] of the intake flow sensor 8, detection value P _in [Pa] of the inlet pressure sensor 9, detection value T _out [K] of the exhaust temperature sensor 11, detection value T _amb of the outside air temperature sensor 12 [K], and the detected value _{V vehicle} [km / h] of the vehicle speed sensor 13 is sent to ECU10 respectively computing device, is used for calculation of the exhaust gas temperature estimation control will be described later.

The ECU 10 is a control unit that controls the entire vehicle including the engine 1. In addition to general engine control, the ECU 10 is based on a detection value of an exhaust temperature sensor 11 disposed downstream of the DOC 5 in this embodiment. Thus, it functions as an exhaust gas temperature estimating device that implements an exhaust gas temperature estimating method for estimating the inlet temperature T _in [K] of the DOC 5. Note that the control logic necessary for carrying out the estimation method is stored in advance in a storage unit such as a memory provided in the ECU 10 as a program, and is configured to be implemented by being appropriately read out by an arithmetic device.
In particular, FIG. 1 shows, as an internal configuration of the ECU 10, functional blocks corresponding to each step of an exhaust gas temperature calculation method described later performed by the ECU 10, and an HC addition detection that detects an HC addition amount by the HC addition device 7. Means 15, oxidation combustion heat quantity calculation means 16 for calculating oxidation combustion heat quantity Q _HC [W], heat _release quantity calculation means 17 for calculating heat _release quantity Q _rad [W], and heat exchange quantity Q _exh [W] The heat exchange amount calculating means 18 for performing the exhaust temperature estimation and the exhaust gas temperature estimating means 19 for obtaining the estimation result of the exhaust gas temperature are included.
In this embodiment, the case where HC is added using the HC addition device 7 is shown, but instead of this, HC may be added using post injection by a fuel injector provided in the engine combustion chamber. Good.

Next, specific contents of the exhaust gas temperature estimation method performed in the ECU 10 will be described. In this exhaust temperature estimation method, by constructing a heat balance model in DOC5, the second exhaust temperature is detected from the first exhaust temperature (the detected value of the exhaust temperature upstream of DOC5 or between DOC5 and DPF6). (Exhaust temperature on the upstream side of DOC5 or on the other side between DOC5 and DPF6) is estimated.
In this embodiment, the exhaust gas temperature value detected by the exhaust gas temperature sensor 11 disposed between the DOC 5 and the DPF 6 is used as the first exhaust gas temperature, and the exhaust gas temperature T _in [K] on the upstream side of the DOC 5 is estimated. This will be described in detail below.
Incidentally, by arranging the exhaust temperature sensor 11 on the upstream side of the DOC 5, when the exhaust temperature detection value on the upstream side of the DOC 5 is used as the first exhaust temperature, the distance between the DOC 5 and the DPF 6 is based on the same technical idea. The exhaust temperature at can be estimated.

FIG. 2 is a diagram conceptually showing a heat balance model of the DOC 5 adopted by the exhaust gas temperature estimation method implemented in the ECU 10. The DOC 5 is given an oxidation combustion heat quantity Q _HC [W] by oxidizing the fuel added by the HC addition device 7 on the upstream side, while heat based on a temperature difference generated between the DOC 5 and the exhaust gas flowing through the DOC 5. An exchange amount Q _exh [W] is generated. Although the influence on the exhaust temperature is small compared to the oxidation combustion heat quantity Q _HC [W] and the heat exchange quantity Q _exh [W], the heat _release quantity Q _rad [W] is based on the temperature difference between the DOC 5 and the outside air. Arise. In the exhaust gas temperature estimation method in the present embodiment, the exhaust temperature can be estimated by modeling the DOC 5 as a heat balance by considering the movement of these three heat quantities.

FIG. 3 is a flowchart showing an implementation process of the exhaust gas temperature estimation method according to the present embodiment.
First, the ECU 10 detects the detected values of each sensor (intake flow rate G _air [kg / s], inlet pressure P _in [Pa], exhaust temperature T _out [K], outside air temperature T _amb [K], vehicle speed V _vehicle [km / h]) is acquired (step S101). Then, using the acquired detection value, an oxidation combustion heat quantity Q _HC [W] given by oxidizing the fuel added from the HC addition device 7 provided on the upstream side of the DOC 5 is calculated (step S102). Then, a heat release amount Q _rad [W] from the DOC 5 to the outside air is calculated (step S103), and a heat exchange amount Q _exh [W] between the DOC 5 and the exhaust gas is calculated (step S104). Finally, the exhaust temperature T _in [K] on the upstream side of the DOC 5 is estimated based on the calculation results of steps S102 to S104 (step S105).
Hereinafter, a specific calculation method in steps S102 to S105 will be described in detail. In FIG. 3, steps S102 to S104 are shown to be performed in order, but these steps may be performed simultaneously.

(Calculation method of oxidation combustion heat quantity Q _HC )
In the oxidation combustion heat quantity calculation means 16 of the ECU 10, the oxidation combustion heat quantity is a heat quantity generated when the HC added to the exhaust gas by the HC addition device 7 undergoes an oxidation reaction at the DOC 5, and roughly, the HC addition quantity q _HC [kg / S] and the lower heating value Hu _fuel [J / kg] of the _fuel , the following formula Q _HC 1 = (q _HC + q _{HC_exh} ) · Hu _fuel (1)
It is requested from. Here, as the HC addition amount q _HC [kg / s], an instruction value for the HC addition device 7 of the ECU 10 is used (in terms of a functional block, the HC addition amount detection means 15 causes the HC addition device 7 to detect the HC addition device 7 as shown in FIG. It is preferable to use a value obtained by reading a representative value stored in advance in a storage unit such as a memory as the lower heating value Hu _fuel [J / kg] of the _fuel . Further, q _HCexh [kg / s] is the HC content contained in the exhaust discharged from the engine, and is an engine speed N _eng that is a detection value of an engine speed sensor (not shown) and an instruction value of the ECU 10. It is calculated by an arbitrary function using the fuel injection amount q _fuel [kg / s] as a parameter.

By the way, when the fuel is excessively added from the HC addition device 7, a part of the fuel flows out to the downstream side of the DOC 5 without being reacted. By adding such unburned components, the oxidation combustion heat quantity Q _HC [W] can be obtained with higher accuracy. The maximum reaction value of the added fuel that can be reacted with DOC5 is expressed by the following equation using the Arrhenius rule: Q _HC 2 = A · N _HC · N _{O 2} · exp (−E / (R · T _{sub (i−1)} ) (2 )
Is obtained. Here, A and E are fitness factors, and R is a gas constant. N _HC [mol / L] and N _O2 [mol / L] are the fuel concentration and the oxygen concentration in the exhaust gas, respectively, the detected value G _air [kg / s] of the intake flow sensor 8, the HC addition device of the ECU 10 HC addition amount instruction value q _HC [kg / s] for 7, HC content q _HCexh [kg / s] contained in exhaust discharged from the engine, fuel injection to the fuel injection device (not shown in FIG. 1) of the ECU 10 It is calculated based on the quantity instruction value q _fuel [kg / s] and the estimated temperature value of DOC5 (previous estimated value of the catalyst temperature) T _{sub (i-1)} obtained when the exhaust gas temperature estimating method was performed last time. it can.

The ECU 10 compares the calculated value Q _HC 1 [W] based on the HC addition amount with the maximum reaction value Q _HC 2 [W] of the added fuel that can react with the DOC 5, and the larger one is the oxidation combustion heat quantity Q _HC [ W].
Q _HC = max (Q _HC 1, Q _HC 2) (3)
As a result, the amount of oxidative combustion heat can be obtained with high accuracy in consideration of the amount that flows out downstream without reacting with the DOC 5 when excessively added from the HC addition device 7.

The oxidation combustion heat quantity Q _HC [W] given to the DOC 5 is distributed to the DOC 5 and the exhaust gas flowing through the DOC 5 at a predetermined ratio d _HCsub (0 ≦ d _HCsub ≦ 1). If the amount of heat distributed to DOC5 and exhaust is Q _HCsub [W] and Q _HCexh [W], respectively,
Q _HCsub = d _HCsub · Q _HC (4)
Q _HCexh = (1-d _HCsub ) · Q _HC (5)
It becomes.

Here, the distribution coefficient d _HCsub is expressed as the following expression d _HCsub = f (G _exh ) (6) as an arbitrary function _having the exhaust flow rate G _exh [kg / s] as a parameter.
Is obtained.
The exhaust flow rate G _exh [kg / s] is expressed by the following equation G based on the detected value G _air [kg / s] of the intake flow rate sensor 8 and the engine fuel injection amount q _fuel [kg / s] which is an engine control parameter. _exh = G _air + q _fuel (7)
Is obtained.

(Calculation method of heat dissipation Q _rad )
The heat release amount calculation means 17 of the ECU 10 calculates the heat release amount Q _rad [W] by considering the temperature difference between the DOC 5 and the outside air and the flow of the outside air around the DOC 5.
First, the ECU 10 has parameters such as kinematic viscosity ν _air [m ² / s], specific heat C _air [J / kg · K], density ρ _air [kg / m ³ ], and thermal conductivity λ _air , which are parameters defining the characteristics of the outside _air. With respect to [W / m · K] and the volume expansion coefficient β _air [1 / K], using arbitrary functions having the detected value T _amb [K] of the outside air temperature sensor 12 as a parameter, the following equation ν _air = f ( T _amb ) (8)
C _air = f (T _amb ) (9)
ρ _air = f (T _amb ) (10)
λ _air = f (T _amb ) (11)
β _air = f (T _amb ) (12)
Ask for.

Subsequently, the Reynolds number Re _amb , the Prandtl number Pr _amb , the Grashof number Gr _amb , and the Nusselt number Nu _amb , which are parameters characterizing the heat transferability of the fluid, are calculated for the outside air flowing around the DOC 5.
Re _amb = v _vehicle · L _sub / ν _air (13)
Pr _amb = C _air · ρ _air · ν _air / λ _air (14)
Gr _amb = L _sub ³ · g · β _air · (T _{sub (i−1)} −T _amb ) / ν _air ² (15)
Nu _amb = c0 · (Gr _amb · Pr _amb ) ^1/3 (v _vehicle = 0) (16-1)
Nu _amb = c1 · Re _amb ^m1 · Pr _amb ⁿ¹ (v _vehicle > 0) (16-2)
Here, v _vehicle is a detected value [km / h] of the _vehicle speed sensor 13, L _sub is a length [m] of the oxidation catalyst, and g is a gravitational acceleration (≈9.80) [m / s ² ]. Yes, T _{sub (i−1)} is the previous estimated value [K] of the catalyst temperature T _sub of the DOC 5 obtained by the exhaust temperature estimating method. c0 is an arbitrary fitness constant. Further, c1, m1, and n1 are complementary functions of the Nusselt number Nu _amb and c1 = f (Re _amb ) (17) using an arbitrary function f.
m1 = f (Re _amb ) (18)
n1 = f (Re _amb ) (19)
Is represented by

Using the above calculation results, the heat transfer coefficient h _amb [W / m ² · K] of the outside air is expressed by the following equation: h _amb = Nu _amb · λ _air / L _sub (20)
The heat transfer coefficient k between the DOC 5 and the outside air is expressed by the following equation k = 1 / (ln (d _cov ) using the cover outer diameter d _cov [m] of the DOC 5 and the outer diameter d _sub [m] of the _{DOC 5.} / D _sub ) / (2 · λ _cov ) + 1 / (h _amb · d _cov )) (21)
Is represented by Therefore, the heat radiation amount Q _rad [W] from the DOC 5 to the outside air is Q _rad = k · π · L _sub · (T _{sub (i−1)} −T _amb ) (22)
It becomes.

(Calculation method of heat exchange amount Q _exh )
The heat exchange amount calculation means 18 of the ECU 10 calculates the heat exchange amount Q _exh [W] by considering the temperature difference between the DOC 5 and the exhaust gas flowing through the DOC 5.
First, the ECU 10 has parameters for defining exhaust characteristics such as kinematic viscosity ν _exh [m ² / s], specific heat C _exh [J / kg · K], density ρ _exh [kg / m ³ ], and thermal conductivity λ _exh. For [W / m · K], using an arbitrary function whose parameter is the previous estimated value T _{in (i−1)} of the inlet temperature of the _{DOC 5} , the following equation ν _exh = f (T _{in (i−1)} ) (23)
C _exh = f (T _{in (i-1)} ) (24)
ρ _exh = f (T _{in (i−1)} ) (25)
_{λ exh = f (T in (} i-1)) (26)
Ask for.

Subsequently, the Reynolds number Re _exh , the Prandtl number Pr _exh , and the _Nusselt number Nu _exh , which are parameters characterizing the heat transferability of the fluid, are calculated for the exhaust gas flowing through the DOC 5.
Re _exh = u _exh · L _sub / ν _exh (27)
v _exh = G _exh · (R / M _exh ) · T _{in (i−1)} / P _in (28)
u _exh = v _exh / (n _sub · p _sub ² ) (29)
Pr _exh = C _exh · ρ _exh · ν _exh / λ _exh (30)
Nu _exh = c 2 · Re _exh ^{m 2} · Pr _exh ⁿ² (31)
Here, c2, m2, and n2 are complementary functions of the _Nusselt number Nu _exh , and c2 = f (Re _exh ) (32) using an arbitrary function f.
m2 = f (Re _exh ) (33)
n2 = f (Re _exh ) (34)
Is represented by

Using the above calculation results, the heat transfer coefficient h _amb [W / m ² · K] of the exhaust gas is expressed by the following equation: h _exh = Nu _exh · λ _exh / L _sub (35)
The heat exchange amount Q _exh [W] from the DOC 5 to the exhaust gas is expressed as Q _exh = h _exh · n _sub · 4 · p _sub · L _sub · (T _{sub (i-1)} -T _in ) (36 )
It becomes.
Note that n _sub is the number of DOC5 cells and p _sub is the cell pitch [m] of DOC5, which may be obtained by reading design values stored in advance in a storage unit such as a memory.

(Method of estimating the exhaust gas temperature _{T in)}
In the exhaust gas temperature estimating means 19 of the ECU 10, the oxidation combustion heat quantity Q _HC [W], the heat radiation quantity Q _rad [W] and the heat exchange quantity Q _exh [W] obtained by the above calculation are used as the heat balance model shown in FIG. As a result, the exhaust temperature T _in [K] on the upstream side of the DOC 5 is expressed by the following equation: T _in = T _out − (Q _HCexh + Q _exh ) / (G _exh · C _exh ) (37)
Is estimated by
Further, the catalyst temperature T _sub [K] of DOC 5 is also expressed by the following formula: T _sub = T _{sub (i−1)} + (Q _HCsub −Q _rad −Q _exh ) / (m _sub · C _sub ) (38)
Is estimated by Note that m _sub is the mass [kg] of DOC5, and C _sub is the characteristic temperature [J / kg · K] of DOC5, which may be obtained by reading a design value stored in advance in a storage unit such as a memory. .

As described above, according to the present embodiment, the oxidation combustion heat quantity Q obtained based on the HC addition amount from the HC addition device 7 by performing the exhaust temperature estimation method in the ECU 10 functioning as the exhaust temperature estimation device. By calculating the amount of heat exchange Q _exh [W] between _HC and DOC5 and exhaust, a heat balance model in DOC5 is constructed, and the first exhaust temperature (upstream of DOC5 or between DOC5 and DPF6) The second exhaust temperature (the exhaust temperature on the upstream side of the DOC 5 or the other between the DOC 5 and the DPF 6) can be estimated from the detected exhaust temperature of either one). Such estimation of the exhaust temperature can be performed under a wide range of conditions regardless of the operating state of the engine 1.
In particular, by incorporating the heat release amount Q _rad [W] from the DOC 5 to the outside air into the heat balance model, the exhaust temperature can be estimated with higher accuracy.
Moreover, since such a heat balance model is closer to the substance compared to a case where a transfer function such as a first-order lag filter as in the prior art is used, a good estimation accuracy can be obtained.

  In this way, the exhaust temperature sensor 11 disposed on either side of the DOC 5 in the exhaust passage 4 can estimate the exhaust temperature on the other side, so there is no need to provide an exhaust temperature sensor on the other side, contributing to the reduction of sensors. By doing so, cost reduction can be achieved.

  The present invention is applicable to an exhaust gas temperature estimation device in which an oxidation catalyst and a DPF are provided in an exhaust gas passage of an internal combustion engine, and an exhaust gas temperature in the exhaust gas passage can be estimated.

1 Engine 2 Air Cleaner 3 Intake Pipe 4 Exhaust Pipe 5 Oxidation Catalyst (DOC)
6 Diesel particulate filter (DPF)
7 HC addition device 8 Intake flow sensor 9 Inlet pressure sensor 10 ECU
DESCRIPTION OF SYMBOLS 11 Exhaust temperature sensor 12 Outside temperature sensor 13 Vehicle speed sensor 15 HC addition amount detection means 16 Oxidation combustion heat amount calculation means 17 Heat release amount calculation means 18 Heat exchange amount calculation means 19 Exhaust temperature estimation means

Claims (5)

An oxidation catalyst is provided in the exhaust passage of the internal combustion engine, and a DPF is provided downstream of the oxidation catalyst, and an exhaust temperature in either the upstream side of the oxidation catalyst in the exhaust passage or between the oxidation catalyst and the DPF is set. An exhaust temperature estimating device for estimating,
Exhaust temperature detection means for detecting a first exhaust temperature on the upstream side of the oxidation catalyst in the exhaust passage or on the other side between the oxidation catalyst and the DPF;
HC addition amount detecting means for detecting the HC addition amount to the oxidation catalyst;
Oxidative combustion heat quantity calculating means for calculating oxidative combustion heat quantity in the oxidation catalyst from the HC addition amount;
Heat exchange amount calculating means for calculating a heat exchange amount between the oxidation catalyst and the exhaust gas flowing through the oxidation catalyst;
An exhaust gas temperature estimation device comprising exhaust gas temperature estimation means for estimating the second exhaust gas temperature in the one based on the detected first exhaust gas temperature, the oxidation combustion heat quantity and the heat exchange quantity. Outside temperature detecting means for detecting outside temperature;
A heat release amount calculating means for calculating a heat release amount from the oxidation catalyst to the outside air from a temperature difference between the outside air and the oxidation catalyst;
The exhaust temperature estimation device according to claim 1, wherein the heat exchange amount calculation unit calculates the heat exchange amount based on the heat dissipation amount.   In the oxidation combustion heat quantity calculating means, the maximum reaction amount of HC that can be reacted with the oxidation catalyst is obtained using the Arrhenius rule with the first exhaust temperature as a parameter, and when the addition amount of HC is larger than the maximum reaction amount of HC, The exhaust temperature estimation device according to claim 1 or 2, wherein the oxidation combustion heat is calculated using the HC maximum reaction amount as the HC addition amount.   The exhaust gas according to any one of claims 1 to 3, wherein the exhaust gas temperature detecting means detects an exhaust gas temperature between the oxidation catalyst and the DPF in the exhaust gas passage as the first exhaust gas temperature. Temperature estimation device.   5. The exhaust gas temperature estimation device according to claim 1, wherein the exhaust gas temperature detection means is provided between the oxidation catalyst and the DPF in the exhaust gas passage.

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