JP4346871B2 - Catalyst temperature estimation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst temperature estimation device suitable for use in vehicles such as automobiles, and more particularly to a catalyst temperature estimation device that estimates the temperature of an exhaust purification catalyst that purifies harmful substances in engine exhaust.
[0002]
[Prior art]
An exhaust purification catalyst (hereinafter simply referred to as a catalyst) interposed in an engine exhaust system is generally sintered (the particles held on the carrier are agglomerated with each other at a high temperature as the temperature becomes higher and the oxidizing atmosphere (lean air-fuel ratio)). As a result, the particle diameter is likely to be deteriorated easily. Accordingly, the heat-resistant temperature of the catalyst is generally lower when the catalyst is in an oxidizing atmosphere than when the catalyst is in a reducing atmosphere (rich air-fuel ratio).
[0003]
For this reason, in order to suppress thermal degradation of the catalyst, it is necessary to accurately avoid a situation where the catalyst is at a high temperature and in an oxidizing atmosphere.
By the way, in recent years, a deceleration fuel cut that temporarily stops (fuel cut) the fuel supply to the engine at the time of deceleration for the purpose of reducing CO ₂ (that is, reducing fuel consumption). Vehicles equipped with the device have been put into practical use.
[0004]
However, at the time of such a deceleration fuel cut, only air is discharged from the cylinder where the fuel is cut, and as a result, the exhaust air-fuel ratio tends to become a lean air-fuel ratio.
Therefore, in the case of such an engine, when the fuel is cut, there are many opportunities for the catalytic converter to be in an oxidizing atmosphere and at a high temperature.
[0005]
Therefore, a technique has been proposed in which the temperature of the catalyst is detected by a temperature sensor and deceleration fuel cut is prohibited when the catalyst temperature becomes high (for example, Japanese Patent Application Laid-Open No. 55-137339). In addition to the above, the catalyst bed temperature is estimated from the intake air amount, and the deceleration fuel cut is prohibited when the catalyst bed temperature is high, or the deceleration fuel cut is prohibited based on the engine speed and the engine load. Have been proposed (for example, JP-A-8-144814).
[0006]
[Problems to be solved by the invention]
However, among such conventional techniques, when it is attempted to directly detect the catalyst temperature using a temperature sensor, it is difficult to attach the temperature sensor to the catalyst carrier, so the catalyst temperature is accurately detected directly. It is not possible. For this reason, the temperature sensor is attached to any position of the catalyst, but in this case, there is a problem that a measurement error occurs. Moreover, since it is necessary to add a temperature sensor newly, there exists a subject of causing a cost increase.
[0007]
Further, in the method of estimating the catalyst temperature from the intake air amount, there is a problem that the estimation accuracy is low because no consideration is given to the exhaust gas temperature. In addition, since the temperature change mechanism differs greatly between when the temperature rises and when the catalyst falls, accurate estimation of the catalyst temperature is possible if the catalyst temperature is estimated using the same method when the temperature rises and falls. There is a problem that it becomes difficult.
[0008]
The present invention has been made in view of such problems, and an object of the present invention is to provide a catalyst temperature estimation device capable of accurately estimating the temperature of a catalyst with a simple configuration.
[0009]
[Means for Solving the Problems]
For this reason, the catalyst temperature estimation device according to the first aspect of the present invention is a catalyst temperature estimation device that estimates the temperature of an exhaust purification catalyst that is provided in an exhaust passage of an engine and purifies harmful substances in exhaust gas. An engine load detecting means for detecting a load; an exhaust flow detecting means for detecting an exhaust flow rate in the exhaust passage; an engine load detected by the engine load detecting means; and an exhaust flow rate detected by the exhaust flow detecting means. and the estimated temperature calculating means for calculating an estimated temperature of the catalyst on the basis, and the catalyst temperature state detecting means to detect the temperature change state of the catalyst, the temperature change state of the catalyst detected by the catalyst temperature state detecting means temperature depending on whether the temperature drop state or in the non-raised position, and the catalyst temperature correcting means for performing different correction on the estimated catalyst temperature is calculated at the estimated temperature calculating means Since provided, it is possible to estimate the catalyst temperature with high accuracy.
In particular, since the catalyst temperature can be estimated without providing new parts such as a temperature sensor, an increase in cost can be avoided. Further, by using the exhaust flow rate when estimating the temperature of the catalyst, cooling of the catalyst by the exhaust flow is taken into consideration, and the catalyst temperature can be estimated with high accuracy. Further, since the catalyst temperature can be estimated with such high accuracy, thermal deterioration of the catalyst can be reliably prevented.
[0010]
The catalyst temperature correcting means changes the corrected catalyst temperature with higher responsiveness to changes in the estimated catalyst temperature when the catalyst is in a temperature rising state than when the catalyst is in a temperature decreasing state. As described above, the estimated temperature is corrected.
With such a configuration, the catalyst temperature can be estimated with higher accuracy. That is, when the temperature of the catalyst rises, the change in the catalyst temperature shows a relatively high response due to the heat received from the exhaust and the reaction heat due to the combustion on the catalyst, while the catalyst temperature falls The change in the catalyst temperature is only the heat release to the exhaust gas, and the response is relatively low. Therefore, when the temperature of the catalyst is rising, the correction is performed so that the response of the corrected change in the catalyst temperature with respect to the change in the estimated catalyst temperature is higher than when the temperature is decreasing, Accurate temperature estimation can be performed.
[0011]
Further, in the catalyst temperature estimation device according to the present invention described in claim 2, the catalyst temperature correction means according to claim 1, wherein the catalyst temperature correction means performs a filter process on the estimated catalyst estimated temperature , and sets a filter constant in the filter process. Since the catalyst is set to be changed between when the temperature is increased and when the temperature is decreased, the catalyst temperature can be accurately estimated according to the temperature change state.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a catalyst temperature estimation device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration, and FIG. 2 is a schematic block diagram showing the main configuration.
An engine 1 shown in FIG. 1 is a so-called in-cylinder injection type spark ignition engine that supplies fuel directly into a cylinder, and includes fuel injection in an intake stroke (intake stroke injection) and fuel injection in a compression stroke (compression stroke). (Injection) can be switched.
[0015]
This in-cylinder injection engine 1 is operated at a stoichiometric air fuel ratio (stoichio), an operation at a rich air fuel ratio (rich A / F) (rich air fuel ratio operation), or a lean air fuel ratio (lean A / F). Operation (lean air-fuel ratio operation) is possible, and the above-mentioned plurality of operation modes are switched according to conditions obtained from various parameters.
The cylinder head 2 of the engine 1 is provided with an ignition plug 4 and a fuel injection valve 6 for each cylinder, and an ignition coil 8 that outputs a high voltage is connected to the ignition plug 4.
[0016]
A fuel supply device (not shown) is connected to the fuel injection valve 6 via a fuel pipe 7. This fuel supply device has a low-pressure fuel pump and a high-pressure fuel pump. After the fuel in the fuel tank is pressurized to a low pressure or a high pressure, the fuel is supplied to the fuel injection valve 6 through the fuel pipe 7. It is supposed to be.
An intake port 9 is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to the upper end of each intake port 9. As shown in the figure, the intake manifold 10 includes a drive-by-wire throttle valve 14 that adjusts the intake air amount, a throttle position sensor (TPS) 16 that detects the opening of the throttle valve 14, and the intake air amount. An intake air amount sensor (air flow sensor or AFS) 18 (mainly used when fuel control is performed by the L Jetronic method) is provided. Furthermore, a pressure sensor 44 [used mainly when fuel control is performed by the speed density method (D Jetronic method)] for detecting the pressure (negative pressure) in the intake manifold 10 is also provided.
[0017]
The cylinder head 2 has an exhaust port 11 for each cylinder, and an exhaust manifold 12 is connected to each exhaust port 11. In addition, an exhaust pipe (exhaust passage) 20 is connected to the exhaust manifold 12, and a three-way catalyst (catalytic converter or simply referred to as a catalyst) 30 is interposed in the exhaust pipe 20 as an exhaust purification catalyst. .
[0018]
The three-way catalyst 30 has any one of copper (Cu), cobalt (Co), silver (Ag), platinum (Pt), rhodium (Rh), palladium (Pd), and iridium (Ir) as an active noble metal. It is configured to oxidize HC and CO in exhaust gas and to reduce and remove NOx. The exhaust pipe 20 is provided with an O ₂ sensor 22.
[0019]
The ECU 40 includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), an arithmetic device (CPU), a timer counter, and the like, and the ECU 40 executes comprehensive control of the engine 1. It has come to be.
Various sensors such as the above-described TPS 16, intake air sensor 18, O ₂ sensor 22, pressure sensor 44, and crank angle sensor 42 that detects the crank angle of the engine 1 are connected to the input side of the ECU 40. Detection information from these sensors is input. The engine speed Ne is calculated based on the crank angle detected by the crank angle sensor 42.
[0020]
Further, the ECU 40 is provided with combustion state control means 410 (see FIG. 2) for controlling the combustion state of the engine. At least one of the intake air amount and the fuel supply amount to the engine 1 by the combustion state control means 410 is provided. Is controlled so that the combustion state of the engine 1 is controlled.
On the other hand, on the output side of the ECU 40, various output devices such as the fuel injection valve 6, the ignition coil 8, and the throttle valve 14 are connected, and these output devices are based on information from various sensors. The air-fuel ratio (A / F) is calculated or set by the combustion state control means 410, and the fuel injection amount (driving pulse width of the fuel injection valve 6), the throttle opening, etc. are set so as to be the A / F. At the same time, signals such as fuel injection timing and ignition timing are output. Thus, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, spark ignition is performed at an appropriate timing by the spark plug 4, and the throttle valve 14 is set to an appropriate opening at an appropriate timing. Is driven to open and close.
[0021]
In addition, the engine 1 is configured to perform so-called deceleration fuel cut control (or simply referred to as fuel cut) in which fuel supply is stopped when the engine 1 is decelerated for the purpose of improving fuel consumption.
That is, as shown in FIG. 2, the ECU 40 is provided with an operating state detecting means 450 for detecting or determining the operating state of the engine 1, and the operating state detecting means 450 further includes a combustion state of the engine 1. Is provided with a combustion state determining means 411 and a deceleration state detecting means (or a deceleration state determining means) 420 for detecting (or determining) whether or not the vehicle is in a decelerating running state.
[0022]
Among them, the deceleration state detecting means 420 includes an accelerator opening sensor (not shown) for detecting or determining the accelerator depression degree and accelerator depression state of the driver, a vehicle speed sensor (not shown) for detecting the vehicle speed, and an engine rotational speed Ne. An engine rotation speed sensor (crank angle sensor 42) to be detected is connected.
The deceleration state detection means 420 determines that the vehicle is in a decelerating running state (or simply referred to as a deceleration state), for example, when it detects a state where the vehicle speed is equal to or higher than a predetermined value and the driver stops depressing the accelerator pedal (accelerator OFF). To do. In addition, when the deceleration state is determined and the state in which the engine rotational speed Ne is equal to or higher than the predetermined rotational speed is detected, the fuel injection from the fuel injection valve 6 is prohibited by the combustion state control means 410. Deceleration fuel cut control is executed.
[0023]
The combustion state control unit 410 also outputs a fuel supply stop unit (not shown) that outputs a signal for stopping the fuel supply to the engine 1 when the deceleration state is determined and the engine rotation speed Ne is equal to or higher than a predetermined rotation speed. (Omitted) is provided.
When the deceleration state detection means 420 determines the deceleration state of the engine 1 (for example, when the driver stops the depression of the accelerator pedal and the engine rotational speed Ne is equal to or higher than a predetermined rotational speed), the combustion state control means By 410, fuel injection from the fuel injection valve 6 is prohibited, and deceleration fuel cut control is executed.
[0024]
In this embodiment, the deceleration fuel cut control is configured to be performed for all cylinders, but may be configured to be performed only for some cylinders. On the other hand, when it is estimated that the catalyst 30 is at a high temperature, this deceleration fuel cut is prohibited for the purpose of protecting the catalyst 30 even if the deceleration state is determined.
[0025]
Hereinafter, the main part of the present invention will be described. As shown in FIG. 2, the ECU 40 has a catalyst temperature estimating means 401 for estimating the temperature of the catalyst 30 based on the engine load L and the exhaust flow rate Q. When the temperature (estimated value) t of the catalyst 30 is equal to or higher than the predetermined value (threshold value) T by the catalyst temperature estimating means 401, the deceleration fuel cut is prohibited to protect the catalyst 30 as described above. Yes.
[0026]
Here, a method for estimating the catalyst temperature in the catalyst temperature estimating means 401 will be described. FIG. 3 shows the data of the actual measured catalyst temperature in a test run or the like. As shown in the figure, there is a linear correlation between the exhaust flow rate and the catalyst temperature using the intake pipe pressure (engine load) as a parameter. Recognize. Therefore, in the present invention, the catalyst temperature is estimated using this characteristic.
[0027]
That is, assuming that the catalyst temperature is t and the exhaust gas flow rate is Q, a linear relationship such as the following equation (1) is established between the catalyst temperature t and the exhaust gas flow rate Q from the experimental results shown in FIG.
t = aQ + b (1)
In the above equation, the values a and b can be calculated from measured data during actual vehicle travel using the least square method, and the value a is a catalyst for the intake pipe pressure as shown in FIG. Prestored in the constant storage means 404 in the temperature estimation means 401. That is, the value a is set to a value corresponding to the intake pipe pressure as the engine load L. The value a is not limited to the intake pipe pressure, and may be set to a value according to a value correlated with the engine load such as volumetric efficiency Ev, intake air amount, throttle opening, and the like. Similarly, the value b may be set to a value corresponding to the engine load L.
[0028]
Further, the catalyst temperature estimating means 401 is provided with a volumetric efficiency map 402 for obtaining the volumetric efficiency Ev as the engine load L, and the intake pipe pressure P and the engine based on the information stored in this map (not shown). The volumetric efficiency Ev is obtained from the rotational speed Ne.
The catalyst temperature estimating means 401 is also provided with an exhaust flow rate calculating means 403 for calculating the exhaust flow rate Q, and the exhaust flow rate Q is calculated by the following equation (2) using the engine rotational speed Ne and the volumetric efficiency Ev. It is like that.
[0029]
Q = 1/2 × total displacement × (Ne / 60) × Ev (2)
However, the unit of the engine speed Ne is [rpm].
In the above description, the volumetric efficiency Ev is applied as the engine load L, and the exhaust flow rate Q is calculated based on the volumetric efficiency Ev. However, in the speed density method (D Jetronic method), the volumetric efficiency Ev (engine load L ) Is obtained from the engine speed Ne and the intake pipe pressure, the crank angle sensor 42 and the pressure sensor 44 constitute an engine load detecting means for detecting the engine load and an exhaust flow rate detecting means for detecting the exhaust flow rate Q. It can be said that The exhaust flow rate Q may be directly calculated from the intake pipe pressure and the engine speed, or may be obtained from the correlation with the intake flow rate detected by the intake air amount sensor 18 in the case of the L Jetronic system.
[0030]
Further, as the exhaust flow rate detecting means, a sensor that actually detects the exhaust flow rate Q may be provided in the exhaust passage 20, or the exhaust flow rate Q may be obtained from a map value correlated with the exhaust flow rate.
In addition to the volumetric efficiency Ev, any parameter representing the engine load may be used as long as it correlates to the engine load, such as intake pipe pressure, intake air amount, throttle opening, and target Pe. May be.
[0031]
Now, referring back to FIG. 2, the catalyst temperature estimation method will be described. As shown in the figure, the catalyst temperature estimation means 401 is provided with estimated temperature calculation means 405 for obtaining an estimated temperature t by calculation. In the temperature calculation means 405, the catalyst temperature t is calculated by the above equation (1).
Further, the catalyst temperature estimating means 401 is provided with a filter processing means (catalyst temperature correcting means) 406 for performing a filter process on the catalyst temperature calculated by the catalyst estimated temperature calculating means 405. When the estimated value of the catalyst temperature t is calculated as described above, a filter process is executed next, thereby stabilizing the estimated catalyst temperature.
[0032]
Specifically, the filter processing means 406 calculates the catalyst temperature filter value by the following equation (3).
Catalyst temperature filter value t ₀ (n) = (1−k) Catalyst temperature filter value t ₀ (n−1)
+ K · Estimated temperature t (3)
Here, k is a filter constant (gain). Then, the catalyst temperature filter value t ₀ processed by the filter processing means 406 is output again as the catalyst temperature.
[0033]
The filter processing unit 406 includes a filter constant changing unit 407 that changes the filter constant according to the temperature change state of the catalyst 30. Here, the filter constant changing means 407 has catalyst temperature state detecting means (not shown) for determining whether the temperature of the catalyst 30 is rising or decreasing, and this catalyst temperature state. The filter constant k is changed based on the detection result of the detection means.
[0034]
In this case, when the catalyst 30 is in the temperature rising state, the correction is performed so that the responsiveness of the catalyst temperature calculated by the estimated catalyst temperature calculating means 405 is higher than that in the temperature decreasing state. It has become. Specifically, the filter constant k is set as a larger value when the catalyst temperature rises than when it falls. This is because the temperature state change mechanism is significantly different between when the temperature of the catalyst 30 rises and when it falls. That is, when the temperature of the catalyst 30 rises, the catalyst 30 receives heat from the exhaust and heat received by the reaction heat of the catalyst 30 (mainly, the combustion heat of unburned matter such as HC, CO ₂ , H _2, etc.). While the temperature state changes with high responsiveness (that is, a large gain), when the temperature of the catalyst 30 decreases, the temperature state changes due to heat release to the exhaust and heat release from the case of the catalyst 30 to the atmosphere, Responsiveness is relatively low (gain is low). In particular, the heat of reaction of the catalyst 30 has a high reaction rate and quick response.
[0035]
Of course, the above-mentioned "heat reception from the exhaust gas and heat reception by the reaction heat of the catalyst 30" and "heat dissipation to the exhaust gas and heat dissipation from the case of the catalyst 30 to the atmosphere" occur both when the catalyst temperature rises and when it falls. When the catalyst temperature increases, the amount of heat received should be greater than the amount of heat released, and the relative balance between the amount of heat received and the amount of heat released differs between when the temperature rises and when the temperature decreases.
[0036]
For this reason, if the same filter constant k is used when the catalyst temperature is rising and when the catalyst temperature is decreasing, the temperature estimation is deviated and it is difficult to correctly estimate the temperature. This has already been confirmed experimentally. Therefore, in the present embodiment, the catalyst temperature is estimated as accurately as possible by separately setting the filter constant k depending on whether the temperature of the catalyst 30 is rising or decreasing.
[0037]
Here, as a method for determining whether the catalyst temperature is increasing or decreasing, the determination is made based on the difference between the current value and the previous value of the catalyst temperature t obtained by the above equation (1). Alternatively, the determination may be made based on the difference between the current (n) value and the previous (n-1) value of the filtered catalyst temperature t ₀ obtained by the above equation (3). However, it is more preferable to determine the difference between the current value and the previous value of the catalyst temperature t because the catalyst temperature can be more accurately estimated immediately before each filter process.
[0038]
On the other hand, as described above, the ECU 40 is provided with the combustion state determination means 411 that determines the combustion state of the engine 1. Further, in the catalyst temperature estimating means 401, a second catalyst temperature correcting means 408 for further correcting the estimated catalyst temperature is provided, and the combustion state determining means 411 causes the combustion state of the engine 1 to be excessively rich in the air-fuel ratio. When it is determined that the state (rich air-fuel ratio) is established, the catalyst temperature is corrected to the low temperature side by the second catalyst temperature correction means 408.
[0039]
This is because the amount of fuel is relatively large during the rich operation, and cooling is performed by the fuel in the cylinder, so that the exhaust temperature is lowered.
In such a rich operation, the second catalyst temperature correction unit 408 corrects the catalyst temperature by multiplying the estimated catalyst temperature filtered by the filter processing unit 406 by a predetermined value (for example, 0.85), for example. It has become so.
[0040]
The correction in the second catalyst temperature correction means 408 is not limited to the above-described method. For example, even if the catalyst temperature is corrected by changing the constants a and b in the above equation (1). Good. In this case, for example, the catalyst temperature is corrected by multiplying the constants a and b by a coefficient of 1 or less, respectively. Further, the correction may be performed by multiplying the value calculated by the above equation (1) by a predetermined value (for example, 0.85).
[0041]
When it is determined that the estimated (calculated) catalyst temperature is equal to or higher than a predetermined value, the deceleration state detecting means 420 determines a deceleration state and determines that the engine rotational speed Ne is equal to or higher than the predetermined rotational speed. Even in this case, the combustion state control means 410 prohibits the deceleration fuel cut so as to protect the catalyst 30.
Further, the ECU 40 is provided with limiting means 440 for limiting the upper limit value and the lower limit value of the catalyst temperature t estimated by the catalyst temperature estimation means 401, and the catalyst temperature is clipped by the upper and lower limit values by the limiting means 440. It is like that.
[0042]
Here, the limiting unit 440 compares, for example, the estimated temperature t and the upper limit value t _MAX , compares the estimated value t with the lower limit value t _MIN , and compares the estimated value t with the lower limit value t _MIN . Maximum value selection means (both not shown) for outputting the larger value, and the estimated temperature value t is limited by the upper and lower limit values by the action of these minimum value selection means and maximum value selection means. It is like that.
[0043]
The clip value (upper limit value t _MAX , lower limit value t _MIN ) may be set differently when the air-fuel ratio is stoichiometric and rich. This is because, as described above, cooling by the fuel can be expected in the rich state than in the stoichiometric state, and the temperature of the catalyst 30 becomes lower. In this case, the clip value is higher when stoichiometric than when rich.
[0044]
By the way, the ECU 40 is provided with a catalyst temperature estimation changing unit 430. When the deceleration state is detected or determined by the deceleration state detection unit 420 provided in the operation state detection unit 450, the catalyst temperature estimation change unit 430 described above. Thus, the catalyst temperature is set to a predetermined value (for example, a fixed value of 650 ° C.) instead of the value set by the estimation method based on the engine load and the exhaust flow rate described above (a method of estimating in the normal operation state). It has come to be.
[0045]
This is because during the fuel cut and during the fuel cut prohibition control, the temperature estimation error in the above temperature estimation formula (1) becomes large due to the following reasons (1) to (3).
(1) Since the intake air amount and the fuel injection amount are small during deceleration, the combustion state is not as good as that during normal operation. For this reason, the exhaust temperature and the unburned components in the exhaust (reacted by the catalyst 30) are different from those during normal operation, and the catalyst temperature is also different.
(2) During deceleration, the amount of intake air, that is, the exhaust flow rate is small, and the catalyst temperature is also different because the cooling (exclusion of heat) by the exhaust flow of the catalyst 30 is less than in normal operation. Note that the cooling of the catalyst by the exhaust flow means that when the catalyst temperature is higher than the exhaust temperature due to the reaction heat of the catalyst 30, heat is held from the catalyst 30 by the exhaust flow and the catalyst 30 is cooled. .
(3) Particularly during fuel cut, fuel injection and combustion are not performed, so the exhaust temperature itself is different from that during normal operation (combustion), and the catalyst temperature is completely different.
[0046]
In addition to the above (1) to (3), in the deceleration state, the degree of catalyst reaction heat generation is highly dependent on the catalyst temperature. Specifically, the higher the catalyst temperature, the higher the degree of activity of the catalyst 30 and the higher the reactivity. Therefore, the reaction of unburned components (HC, CO, H _2, etc.) in the exhaust gas becomes active, and the catalyst temperature is further increased. Become.
Further, the heat amount of the carrier (including the washcoat) of the catalyst 30 at the start of the fuel cut control or the fuel cut prohibition control is released during the fuel cut control or the fuel cut prohibition control, and the catalyst temperature rises. Is correlated to the catalyst temperature (more precisely, the catalyst temperature at the start of deceleration).
[0047]
For these reasons, the heat of reaction at the catalyst 30 has a great influence on the catalyst temperature when determining the deceleration state, and it is difficult to estimate the temperature with high accuracy using the above-described estimated temperature calculation formula (1).
Therefore, in such a deceleration state, in this embodiment, the estimated catalyst temperature is set to a predetermined value t ₁ (for example, 650 ° C.).
[0048]
Although the above description is an example when the predetermined value t ₁ is a fixed value, the predetermined value t ₁ is, for example, the estimated catalyst temperature t [estimated temperature calculated by the equation (1) at the time of deceleration state determination] ] May be set as a map. Further, the predetermined value t ₁ may be a map corresponding to any one of the catalyst temperature, the exhaust flow rate, the air-fuel ratio, the fuel injection amount, and the catalyst carrier capacity (including washcoat) at the time of determining the deceleration state. Of the above-mentioned parameters, the catalyst carrier capacity is a constant value and is not a value that varies depending on the running state. Therefore, when this catalyst carrier capacity is used, it is applied in combination with other parameters.
[0049]
Further, the fuel cut control state (that is, the accelerator is off, the engine rotational speed Ne is equal to or higher than the predetermined rotational speed, and the catalyst temperature is lower than the predetermined value) by the deceleration state determining means 420 provided in the operating state detecting means 450. Or the fuel cut prohibition control state (that is, the accelerator is off, the engine speed Ne is equal to or higher than a predetermined speed, and the catalyst temperature is equal to or higher than a predetermined value). Based on the above, the predetermined value t ₁ may be set to a different value. In this case, it is preferable to set the estimated catalyst temperature value during the deceleration fuel cut to be smaller than the estimated catalyst temperature value during the fuel cut prohibition control. This is because during the deceleration fuel cut, fuel injection is prohibited and combustion is not performed, so that the exhaust temperature is different and the catalyst temperature is greatly different from when the fuel cut is prohibited (combustion).
[0050]
As described above, when the estimated temperature value t of the catalyst 30 is equal to or greater than the predetermined value (threshold value) T, the deceleration fuel cut is prohibited to protect the catalyst 30. In this case, the operation is performed at the rich air / fuel ratio or stoichiometric air / fuel ratio.
The threshold value T is set to a temperature at which the catalyst 30 starts to deteriorate in a lean atmosphere (lean heat resistance temperature). This value varies depending on the catalyst, but is approximately 700 to 900 ° C.
[0051]
Since the catalyst temperature estimation apparatus according to an embodiment of the present invention is configured as described above, the catalyst temperature is estimated as follows.
First, based on the engine rotational speed Ne and the intake pipe pressure P detected by the crank angle sensor 42 and the pressure sensor 44, the volume efficiency map 402 calculates the volume efficiency Ev (engine load L). Further, the exhaust flow rate calculation means 403 calculates the exhaust flow rate Q from the engine rotational speed Ne and the volumetric efficiency Ev by the above equation (2).
[0052]
On the other hand, constants a and b are set from the intake pipe pressure P based on a map stored in advance in the constant storage means 404. Then, in the estimated temperature calculation means 405, the catalyst temperature t is calculated by the above equation (1) using the constants a and b and the exhaust flow rate Q.
Next, in the filter processing means 406, the filter process is executed from the above equation (3), and the catalyst temperature t is stabilized. Then, the catalyst temperature filter value t ₀ processed by the filter processing means 406 is output again as the catalyst temperature t.
[0053]
Further, the filter constant k used in the equation (3) is changed by the filter constant changing means 407 according to the temperature change state of the catalyst 30. In this case, the filter constant k is set to a different value depending on whether the temperature of the catalyst 30 is increasing or decreasing. Specifically, the filter constant k is larger when the catalyst temperature is higher than when it is decreased. Set as
[0054]
Further, when the combustion state determining unit 411 determines that the air-fuel ratio of the engine 1 is in an excessively rich state (rich), the second catalyst temperature correcting unit 408 takes into consideration the temperature drop (fuel cooling) of the exhaust due to fuel. Thus, the catalyst temperature t is corrected to the low temperature side. In this case, for example, the catalyst temperature is corrected by multiplying the value calculated by the above equation (1) by a predetermined value (for example, 0.85).
[0055]
If the deceleration state is detected or determined by the deceleration state detection unit 420, the catalyst temperature estimation change unit 430 replaces the catalyst temperature t estimated as described above with, for example, the estimated catalyst temperature = predetermined value t ₁ ( For example, it is determined whether the fuel cut control state or the fuel cut prohibition control state is set, and the estimated catalyst temperature t ₁ is set based on the determination result. Thereafter, the catalyst temperature t is clipped at the upper limit value and the lower limit value by the limiting means 440.
[0056]
If the estimated catalyst temperature t is equal to or higher than the predetermined value T, the combustion state control means 410 protects the catalyst 30 even if the deceleration state is detected by the deceleration state detection means 420 and the fuel is cut by the deceleration fuel. Is prohibited.
FIG. 5 is a diagram showing a comparison between the actual measured value of the temperature of the catalyst 30 and the catalyst temperature t obtained by the above equation (1). As shown in the figure, according to the present invention, the temperature of the catalyst 30 is highly accurate. Could be estimated. Note that when the air-fuel ratio is in the rich region and correction is not performed when rich, the estimated value of the catalyst temperature is higher than the actually measured value. However, as described above, in the rich region, the catalyst temperature correction is performed. Since the catalyst temperature t is corrected to the low temperature side by means 408 (rich time correction), a catalyst temperature closer to the actually measured value can be obtained even in the rich region.
[0057]
Thus, in the catalyst temperature estimation device according to one embodiment of the present invention, the temperature of the catalyst 30 is estimated based on the volumetric efficiency Ev as the engine load and the exhaust flow rate Q. Therefore, the catalyst temperature is set without providing a temperature sensor. The cost can be estimated and an increase in cost can be avoided.
In this embodiment, since the exhaust flow rate Q is used as a parameter for estimating the temperature of the catalyst 30, cooling of the catalyst 30 by the exhaust flow is also taken into consideration, and there is an advantage that the catalyst temperature can be estimated with high accuracy. is there. Further, since the catalyst temperature can be estimated with such high accuracy, there is an advantage that the thermal degradation of the catalyst 30 can be surely prevented, and only when necessary (only when the catalyst 30 is at a high temperature above a predetermined temperature). There is an advantage that fuel cut control can be executed with high accuracy.
[0058]
Further, by applying a filter process to the catalyst temperature, the estimated catalyst temperature can be stabilized, and the estimation accuracy of the catalyst temperature can be further increased.
In addition, when the catalyst 30 is in a temperature rising state, the estimated temperature is corrected so that the responsiveness of the catalyst temperature is higher than when the catalyst 30 is in a temperature decreasing state. be able to. That is, when the temperature of the catalyst 30 rises, the change in the catalyst temperature shows a relatively high response due to the heat received from the exhaust gas and the heat received from the reaction heat on the catalyst 30, whereas the temperature of the catalyst 30 decreases. The responsiveness is relatively low because the temperature is only lowered by the heat radiation to the exhaust and the heat radiation to the atmosphere. Therefore, when the temperature of the catalyst is increasing, it is possible to perform accurate temperature estimation by performing correction so that the responsiveness of the catalyst temperature is higher than when the temperature is decreasing.
[0059]
Specifically, the catalyst temperature can be estimated with higher accuracy by setting the filter constant k in accordance with the temperature change state (temperature increase or decrease) of the catalyst 30.
In addition, when the combustion state is a rich air-fuel ratio, the estimated catalyst temperature is corrected to the low temperature side, so that the temperature drop due to fuel cooling is also taken into consideration, and the catalyst temperature can also be estimated with high accuracy. It becomes possible.
[0060]
Further, by setting the catalyst temperature to a value (for example, a predetermined value t ₁ = 650 ° C.) set by a method different from the above equation (1) during the deceleration state, the catalyst temperature 30 can be accurately set even during deceleration. There are advantages that can be estimated. In other words, when decelerating, the exhaust temperature and unburned components in the exhaust are different from those during normal operation, and there is less cooling due to the exhaust flow (heat removal). When the catalyst temperature is estimated by the above equation (1), Temperature estimation error increases.
[0061]
On the other hand, the present invention has an advantage that the catalyst temperature can be estimated with high accuracy even during the deceleration state by changing the catalyst temperature estimated during the normal operation to another value during the deceleration state. is there.
Further, it is judged whether or fuel cut prohibiting control mode is a fuel cut control state during deceleration state, when configured to set the predetermined value t ₁ of the catalyst temperature on the basis of this determination result to different values This makes it possible to estimate the catalyst temperature with higher accuracy even in the deceleration state.
[0062]
The embodiment of the present invention is not limited to the above, and various modifications can be made without departing from the spirit of the present invention. For example, a state in which fuel cut control can be performed (that is, a state where the accelerator is OFF and the engine rotational speed Ne is equal to or higher than a predetermined rotational speed) is determined as a deceleration state, and the catalyst temperature is changed to another value in this deceleration state. You may do it.
[0063]
In this embodiment, the catalyst temperature estimated according to the engine load and the exhaust flow rate is corrected differently according to the temperature change state of the catalyst. However, the catalyst temperature estimated by other methods is used. Similarly, different corrections may be performed on the directly detected catalyst temperature depending on the temperature change state of the catalyst. In the present embodiment, a case where a so-called in-cylinder injection type spark point internal combustion engine is applied as the engine 1 has been described. However, the engine to which the present invention is applied is not limited to this, and diesel engine It may be applied to the engine. In the present embodiment, the case where a three-way catalyst is used as the catalyst 30 has been described. However, various catalysts such as a NOx catalyst can be applied to the catalyst 30.
[0064]
【The invention's effect】
As described above in detail, according to the catalyst temperature estimation device of the present invention described in claim 1, the estimated catalyst temperature is determined depending on whether the temperature change state of the catalyst is the temperature increase state or the temperature decrease state. Therefore, there is an advantage that the catalyst temperature can be estimated with high accuracy.
[0065]
In addition, when the catalyst is in the temperature rising state , the corrected catalyst temperature changes with higher responsiveness to the change in the estimated catalyst temperature than in the temperature lowered state . By performing the correction, there is an advantage that more accurate temperature estimation can be performed. In addition, a simple configuration in which the temperature of the catalyst is estimated based on the engine load detected by the engine load detection means and the exhaust flow rate detected by the exhaust flow rate detection means allows new parts such as a temperature sensor to be installed during deceleration operation. There is an advantage that the catalyst temperature can be estimated without providing it, and thus an increase in cost can be avoided. Further, by using the exhaust flow rate when estimating the temperature of the catalyst, cooling of the catalyst by the exhaust flow is taken into consideration, and the catalyst temperature can be estimated with high accuracy. In addition, since the catalyst temperature can be estimated with such high accuracy, there is an advantage that the thermal deterioration of the catalyst can be surely prevented.
According to the catalyst temperature estimating apparatus of the present invention as set forth in claim 2, in addition to the advantage of claim 1, the catalyst is subjected to the filter process and the filter constant in the filter process is in a temperature rising state. Since it changes with the case where it is in a case and a temperature fall state, there exists an advantage which can estimate a catalyst temperature correctly according to a temperature change state.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an overall configuration of a catalyst temperature estimation apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic block diagram showing a main configuration of a catalyst temperature estimation device according to an embodiment of the present invention.
FIG. 3 is a diagram showing measured data of catalyst temperature obtained in the process of creating a catalyst temperature estimation device according to an embodiment of the present invention.
FIG. 4 is an example of a map stored in a constant storage unit of the catalyst temperature estimation device according to the embodiment of the present invention.
FIG. 5 is a diagram for explaining the operation and effect of the catalyst temperature estimation device according to the embodiment of the present invention.
[Explanation of symbols]
1 Engine 20 Exhaust pipe (exhaust passage)
30 Catalyst (Exhaust gas purification catalyst)
42 Crank angle sensor 44 as engine load detection means and exhaust flow rate detection means 44 Pressure sensor 401 as engine load detection means and exhaust flow rate detection means Catalyst temperature estimation means 406 Filter processing means 407 as catalyst temperature correction means Filter constant change means 408 Second catalyst temperature correction means 411 Combustion state determination means 420 Deceleration state detection means 430 Catalyst temperature estimation change means 450 Operating state detection means

Claims (2)

In a catalyst temperature estimation device that estimates the temperature of an exhaust purification catalyst that is provided in an exhaust passage of an engine and purifies harmful substances in exhaust,
Engine load detecting means for detecting the load of the engine;
An exhaust flow rate detecting means for detecting an exhaust flow rate in the exhaust passage;
And the estimated temperature calculating means for calculating an estimated temperature of the catalyst based on the exhaust flow rate detected by the detected engine load and the exhaust gas flow rate detection means in the engine load detecting means,
Catalyst temperature state detecting means for detecting a temperature change state of the catalyst;
Depending on whether the temperature change state of the catalyst detected by the catalyst temperature state detecting means is a temperature rising state or a temperature lowering state, it differs from the estimated catalyst temperature calculated by the estimated temperature calculating means And a catalyst temperature correction means for performing correction,
The catalyst temperature correcting means may change the corrected catalyst temperature with higher responsiveness to a change in the estimated catalyst temperature when the catalyst is in a temperature rising state than in a temperature lowering state. , let row correction on the estimated catalyst temperature
Characterized the this, the catalyst temperature estimating unit. The catalyst temperature correcting means performs a filtering process on the estimated estimated catalyst temperature , and changes a filter constant in the filtering process depending on whether the catalyst is in the temperature increasing state or the temperature decreasing state. The catalyst temperature estimation device according to claim 1, wherein the catalyst temperature estimation device is set as follows.

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