JPH1182143A - Catalyst temperature estimating device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate the change of catalyst temperature from the stop time of an engine until the start time of the engine, and the initial temperature of a catalyst at the start time of the engine. SOLUTION: A catalyst temperature estimating device has estimated catalyst temperature information with an estimated catalyst temperature curve protruded upward from the stop time of an engine until the lapse of specified time and with the estimated catalyst temperature curve protruded downward from the time after the lapse of specified time until the time of estimated catalyst temperature reaching intake air temperature, taking account of the fact that a catalyst continues to generate heat of reaction even when the catalyst in a catalyst device is not cooled due to the stop of exhaust gas flow from the stop time until the lapse of specified time. The catalyst temperature estimating device can accurately estimate the change of catalyst temperature from the stop time of the engine until the following start time of the engine and the initial temperature of the catalyst at the time of starting the engine from the estimated catalyst temperature information, the estimated catalyst temperature at the stop time of the engine and elapsed time from the engine stop time to the engine start time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst temperature estimating device for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, from the time when an engine is stopped to the time when the next engine is started, based on a water temperature or the like that decreases monotonically in a convex manner,
2. Description of the Related Art A catalyst temperature estimating device for an internal combustion engine that estimates that a catalyst temperature is convexly and monotonically decreasing downward is known. An example of this type of catalyst temperature estimating apparatus for an internal combustion engine is described in, for example, Japanese Patent Application Laid-Open Publication No. 95-10884. The apparatus described in Japanese Patent Application Laid-Open No. 95-10884 discloses a catalyst temperature estimating device that estimates the catalyst initial temperature at the time of starting the engine, and further calculates the catalyst temperature rise from the integrated value of the intake air amount after the engine is started. Is estimated, and the OTP increase start timing is determined.

[0003]

However, the catalyst temperature estimating apparatus for an internal combustion engine described in the above-mentioned Japanese Patent Application Publication No. 95-10884 discloses that the catalyst temperature decreases from the time when the engine is stopped until the next time the engine is started. Although it is estimated that the catalyst temperature monotonically decreases, the catalyst temperature does not actually decrease monotonically downward from the time when the engine is stopped until the next time the engine is started for the following reason.

[0004] Before the engine is stopped, the catalyst generates reaction heat due to a chemical reaction. However, since the catalyst is exposed to the flow of exhaust gas, the catalyst temperature is stable at a substantially constant value. When the engine is stopped, the flow of exhaust gas stops, and the catalyst is not cooled by the flow of exhaust gas. On the other hand, even when the engine is stopped, the catalyst continues to generate reaction heat by a chemical reaction until a predetermined time has elapsed after the engine is stopped. Therefore, the catalyst temperature does not monotonically decrease downward from the time when the engine is stopped until a predetermined time elapses after the engine is stopped, and the amount of decrease per unit time tends to increase as the time elapses. is there.

As described above, the conventional catalyst temperature estimating apparatus for an internal combustion engine erroneously estimates that the catalyst temperature decreases monotonically downward from the time the engine is stopped until the time the next engine is started. Therefore, the catalyst initial temperature at the time of starting the engine cannot be accurately estimated.

In view of the above problems, the present invention accurately estimates a change in catalyst temperature from the time when the engine is stopped to the time when the next engine is started, and is therefore able to accurately estimate the catalyst initial temperature when the engine is started. It is an object of the present invention to provide a catalyst temperature estimating device for an internal combustion engine that can be used.

[0007]

According to the first aspect of the present invention, the estimated catalyst temperature curve is convex upward from the time when the internal combustion engine is stopped to the time when a predetermined time elapses, and the predetermined time elapses. From the time until the time when the estimated catalyst temperature reaches the outside air temperature, the estimated catalyst temperature curve in which the estimated catalyst temperature curve is convex downward, the estimated catalyst temperature when the internal combustion engine is stopped, and the estimated A catalyst temperature estimating device for an internal combustion engine is provided, which estimates a catalyst initial temperature at the time of starting the internal combustion engine from an elapsed time until the start of the engine.

According to the first aspect of the present invention, there is provided a catalyst temperature estimating apparatus for an internal combustion engine, which is provided between a time when the internal combustion engine is stopped and a time when a predetermined time elapses.
Even if the flow of exhaust gas is stopped and the catalyst is not cooled by the flow of exhaust gas, the estimated catalyst temperature curve is not It is set to be convex. Therefore, compared with the case where the estimated catalyst temperature curve is set to be always convex downward, it is possible to accurately estimate the catalyst temperature change from the time when the internal combustion engine is stopped to the time when the next internal combustion engine is started. Therefore, the catalyst initial temperature at the time of starting the engine can be accurately estimated.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing an embodiment of a catalyst temperature estimating apparatus for an internal combustion engine according to the present invention. In FIG. 1, 1 is an engine, 2 is an intake pipe for supplying intake air to the engine 1, 3 is an air flow meter provided in the intake pipe 2, and 4 is an exhaust pipe for discharging exhaust from the engine 1. . Reference numeral 5 denotes a catalyst device provided in the exhaust pipe 4 for purifying unpurified components in exhaust gas. Reference numeral 6 denotes an air-fuel ratio sensor provided in the exhaust pipe 4 downstream of the engine 1 and upstream of the catalyst device 5. And 7 are oxygen concentration sensors provided in the exhaust pipe 4 on the downstream side of the catalyst device 5. Reference numeral 8 denotes a water temperature sensor for detecting the temperature of the engine cooling water, 9 denotes an intake air temperature sensor for detecting the temperature of the intake air, and 10 denotes a catalyst deterioration abnormality display section for displaying catalyst deterioration abnormality. An ECU 11 is electrically connected to the air-fuel ratio sensor 6, the oxygen concentration sensor 7, the water temperature sensor 8, the intake air temperature sensor 9, and the catalyst deterioration abnormality display.

As shown in FIG. 1, in an engine 1, intake air supplied through an intake pipe 2 and fuel supplied by a fuel injection device (not shown) are burned. In the exhaust gas generated by the combustion, unpurified components in the exhaust gas are purified by the catalyst device 5 and discharged through the exhaust pipe 4. However, since the exhaust gas discharged from the engine 1 is very hot,
The exhaust gas raises the temperature of the catalyst in the catalyst device 5. If the catalyst temperature rises excessively, the purification performance of the catalyst device 5 decreases, and it becomes impossible to sufficiently purify the unpurified components thereafter. Therefore, the catalyst temperature estimation device for an internal combustion engine of the present embodiment estimates the catalyst temperature by a catalyst temperature estimation method described later. As a result, it is possible to determine the start time of the OTP increase (to increase the supply fuel in order to prevent abnormal heating of the catalyst). By increasing the OTP, the catalyst device 5 can always sufficiently purify the unpurified components in the exhaust gas. Less than,
The catalyst temperature estimating method of the present embodiment will be described.

FIG. 2 is a flowchart showing a catalyst initial temperature estimating method for estimating a catalyst initial temperature which is a catalyst temperature at the time of starting the engine. As shown in FIGS. 1 and 2, when the catalyst initial temperature estimation is started, first, in step 10
In 1, the intake air temperature sensor 9 detects the intake air temperature T1 at the present engine start time ta. Since the intake air temperature is substantially equal to the outside air temperature, as shown in FIG. 3, from the previous engine stop time t0 to the current engine start time ta, although there is a temperature change of the degree of the temperature change, it is almost constant at the temperature T1. It has become. FIG. 3 is a graph showing the relationship between the elapsed time since the engine was stopped and the intake air temperature. Subsequently, at step 102, when the engine is stopped immediately before the current engine start time ta (that is, at time t0 in FIG. 3).
Is read. This water temperature is determined when the engine is stopped.
0 is detected by the water temperature sensor 8 and R
This is what was stored in the AM.

Returning to FIG. 2, in step 103, the intake air temperature T1 detected in step 101, the engine-stop water temperature T3 read in step 102, and the previously stored RAM in the ECU 11 as shown in FIG. An appropriate water temperature curve indicating a change in water temperature from the time t0 when the engine is stopped to the time ta when the engine is started is selected from the water temperature model curve map. FIG. 4 shows a water temperature curve W1 in which the water temperature at the predetermined temperature T4 when the engine is stopped changes to a temperature equal to the intake air temperature T2 (that is, the outside air temperature), and the water temperature at the predetermined temperature T4 when the engine is stopped is changed to the intake air temperature T1. The water temperature curve W2 changes to an equal temperature (that is, the outside temperature), the water temperature curve W3 changes from the predetermined temperature T3 when the engine stops to a temperature equal to the intake temperature T2 (that is, the outside temperature), and the predetermined temperature T3 when the engine stops. The temperature of the intake water is T1
Temperature curve W that changes to a temperature equal to
4 is a water temperature model curve map including a plurality of water temperature curves, such as 4. In step 103 described above, the water temperature at the time t0 when the engine is stopped is T3 from step 102, and further, in step 101, the outside temperature T1 at which the temperature at which the water temperature curve stabilizes after a predetermined time has elapsed since the engine was stopped is equal to the intake air temperature T1.
Therefore, the water temperature curve W4 is selected from the water temperature curves W1 to W4 in the water temperature model curve map of FIG.

Returning to FIG. 2, in step 104, the water temperature sensor 8 detects the current water temperature Ta at the time of starting the engine. Subsequently, in step 105, the time ta at the point where the water temperature is Ta on the water temperature curve W4 is calculated from the water temperature model curve map in FIG. 4, and the elapsed time from the engine stop time t0 to the engine start time ta (ta−t) is calculated.
0) is calculated. Subsequently, in step 106, the estimated catalyst temperature T5 at the time of the engine stop t0 is read. This estimated catalyst temperature T5 is calculated at the engine stop time t0 by an engine operating catalyst temperature estimation device described later,
This is stored in the RAM in the CU 11.

Next, at step 107, the estimated catalyst temperature T5 at the engine stop time t0 read at step 106 and the estimated catalyst temperature model curve map previously stored in the RAM in the ECU 11 as shown in FIG.
An appropriate estimated catalyst temperature curve indicating a change in the estimated catalyst temperature from the engine stop time t0 to the engine start time ta is selected. FIG. 5 shows an estimated catalyst temperature curve C1 in which the estimated catalyst temperature at the predetermined temperature T6 when the engine is stopped changes to a temperature equal to the intake air temperature T2 (that is, the outside air temperature), and the estimated catalyst at the predetermined temperature T6 when the engine is stopped. Temperature is intake temperature T1
The estimated catalyst temperature curve C2 changes to a temperature equal to (ie, the outside temperature), and the temperature at which the estimated catalyst temperature, which was the predetermined temperature T5 when the engine was stopped, is equal to the intake temperature T2 (ie, the outside temperature)
A plurality of estimated catalyst temperature curves, such as an estimated catalyst temperature curve C3 that changes to a predetermined temperature T5 when the engine is stopped and an estimated catalyst temperature curve C4 that changes to a temperature equal to the intake air temperature T1 (that is, the outside temperature) when the engine is stopped. It is an estimated catalyst temperature model curve map provided. In step 107 described above, the estimated catalyst temperature is T5 at the engine stop time t0 from step 106, and further from step 101, the temperature at which the estimated catalyst temperature curve stabilizes after a lapse of a predetermined time from the engine stop is equal to the intake air temperature T1. Since the temperature is T1, the estimated catalyst temperature curve C4 is selected from the estimated catalyst temperature curves C1 to C4 in the estimated catalyst temperature model curve map in FIG.

As shown in FIG. 5, the estimated catalyst temperature curves C1 to C4 of this embodiment are upwardly convex from the engine stop time t0 to the time tb, and at the time t
From b, it protrudes downward until time tc when the estimated catalyst temperature reaches a temperature equal to the intake air temperature T1, T2. The reason will be described later.

Returning to FIG. 2, in step 108, the estimated catalyst temperature curve C4 selected in step 107
And the elapsed time (ta−t0) from the engine stop time t0 to the engine start time ta calculated in step 105, the estimated catalyst initial temperature Tb at the engine start time ta (FIG. 5).
Is calculated, and the catalyst initial temperature estimation is completed.

As shown in FIGS. 1 and 5, at the engine stop time t0, the flow of exhaust gas in the catalyst device 5 is stopped by stopping the engine 1. Therefore, when the engine is stopped t
After 0, the catalyst device 5 is not cooled by the flow of the exhaust gas. However, even after the engine is stopped, the catalyst in the catalyst device 5 generates reaction heat due to a chemical reaction from the time of the engine stop t0 to the time tb. Therefore, after the engine is stopped, the actual catalyst temperature does not suddenly decrease as shown by the conventional estimated catalyst temperature curve C ′ (FIG. 5), but the estimated catalyst temperature curve C of the present embodiment.
As shown by 1 to C4, a state in which the amount of reduction per unit time increases as the time elapses for a while continues. In consideration of the above points, the estimated catalyst temperature curves C1 to C4 of the present embodiment do not suddenly decrease after the engine is stopped as in the conventional estimated catalyst temperature curve C ', but for a while after the engine is stopped. It is set so as not to decrease, that is, to protrude upward from the engine stop time t0 to the time tb. Therefore, the catalyst temperature estimating device for an internal combustion engine of the present embodiment can accurately determine the catalyst initial temperature at the engine start time ta as compared with a conventional catalyst temperature estimating device for an internal combustion engine in which the estimated catalyst temperature curve is incorrectly set. Can be estimated.

In the above embodiment, step 101 is executed.
From step 105, the elapsed time from the engine stop time t0 to the engine start time ta is calculated in step 105. However, in another embodiment, instead of steps 101 to 105, the engine stop time t
It is also possible to calculate the elapsed time from 0 to the engine start time ta.

Hereinafter, the energy used in step 106 of FIG.
The method for calculating the estimated catalyst temperature at engine shutdown will be described.
You. FIG. 6 shows a routine executed at predetermined time intervals.
Estimated touches during engine operation showing only the nth routine
It is a flowchart of a medium temperature calculation method. 1 and 6
Starts the n-th routine for calculating the estimated catalyst temperature
Then, first, in step 201, the previous route
In other words, E calculated by the (n-1) th routine
The catalyst temperature tcat stored in the CU 11_n-1Read
Put in. Here, when n = 1, that is, immediately after engine start
In the latter case, it is calculated by the catalyst initial temperature estimation method of FIG.
The estimated estimated catalyst initial temperature is the catalyst temperature tcat _n-1As
used.

Since the amount of heat supplied to the catalyst by the exhaust gas is proportional to the amount of intake air, subsequently, at step 202, the amount of intake air ga detected by the air flow meter 3 and EC
From the constant K1 stored in advance in U11, the amount of heat Qg _n (= K1 × ga) supplied to the catalyst by the exhaust gas is calculated. Since the exhaust system has a capacity, it takes time for the detected intake air to reach the catalyst. This time
It is inversely proportional to the intake air amount and the exhaust temperature, and is proportional to the exhaust pressure. By utilizing this relationship, it is possible to recognize when the exhaust gas that has now passed through the catalyst has passed through the air flow meter. Alternatively, the volume of exhaust gas passing through the catalyst for each routine and the volume of the air passage from the air flow meter to the catalyst device can be used to determine when the exhaust gas currently passing through the catalyst has passed through the air flow meter. It is possible. In this case, the exhaust gas volume Vg (= (ga / M) × R) that passes through the catalyst for each routine is obtained based on the intake air amount ga, the molecular weight M of the exhaust gas, the gas constant R, the exhaust temperature Tg, and the exhaust pressure Pg.
× Tg / Pg) is calculated.

The amount of heat released from the outer wall of the catalyst device 5 per unit time is substantially proportional to the difference between the catalyst temperature tcat and the outside air temperature (substantially equal to the intake air temperature _{th). -1,} and the intake air temperature tha detected by the intake air temperature sensor 9, the constant K2 Metropolitan stored in advance in the ECU 11, heat is released from the outer wall of the catalytic converter _{5 Qo n (= K2 × (} tcat n-1 −
tha)). In _order to accurately calculate the amount of heat Qon released from the outer wall of the catalyst device 5, the catalyst temperature t
cal based on the integrated value of the difference between cat and intake air temperature th.
_{o n (= K2 × (Σ} (ai × tcat i -bi × tha
_i )), where ai and bi are coefficients).

The amount of heat generated by the chemical reaction of the catalyst is proportional to the amount of exhaust gas passing through the catalyst device 5 and the reaction coefficient of the catalyst. Here, the reaction coefficient of the catalyst is determined by comparing the catalyst temperature with that of FIG.
Has the relationship shown in FIG. FIG. 7 shows the catalyst temperature tca.
5 is a graph showing the relationship between t and the reaction coefficient Map (tcat), where the reaction coefficient Map (tcat) is the catalyst temperature tc.
It increases as at increases. Based on the above,
Subsequently, in step 204, the reaction coefficient Map (tca) calculated from the catalyst temperature tcat and the graph of FIG.
t), the intake air amount ga, and the constant K3 stored in the ECU 11 in advance, the heat amount Q generated by the reaction in the catalyst.
r _n (= K3 × gn × Map (tcat)) is calculated.

Since the catalyst temperature change Δtcat is proportional to the amount of heat flowing into and out of the catalyst, the process proceeds to step 205.
, The amount of heat Qg supplied to the catalyst by the exhaust
and _n, the amount of heat Qo _n emitted from the outer wall of the catalytic converter 5,
And the amount of heat Qr _n generated by the reaction in the catalyst, ECU 11
From the constant K4 stored in advance in the catalyst temperature change amount Δ
_{tcat n (= K4 × (Qg} n + Qo n + Qr n)) is calculated. Subsequently, at step 206, the catalyst temperature t
The catalyst temperature tcat _n (= tcat _n-1 + Δtcat _n ) is calculated from the cat _n-1 and the catalyst temperature change amount Δtcat _n . As described above, it is possible to calculate the estimated catalyst temperature at any time during the operation of the engine, that is, at any time from the start of the engine to the stop of the engine. The estimated catalyst temperature when the engine is stopped calculated in step 206 is used in step 106 of FIG. 2 described above.

Using the estimated catalyst initial temperature at the time of engine start and the estimated catalyst temperature from the time of engine start to the time of engine stop accurately calculated by the estimated catalyst temperature calculation method of FIGS. It is also possible to make a deterioration determination. FIG. 8 is a flowchart showing a catalyst deterioration determination method using the catalyst temperature accurately estimated according to the present embodiment. 1 and 8, when the catalyst deterioration determination is started, first, in steps 301 and 302, a catalyst upstream-side oxygen concentration change amount integrated value va described later
byfloc _n and the integrated value vo of the change in oxygen concentration on the downstream side of the catalyst
xloc _n is initialized. Subsequently, in step 303, n = 1, and in step 304, the air-fuel ratio sensor 6 and the oxygen concentration calculation sensor 7 use the catalyst upstream oxygen concentration vabyf _n and the catalyst downstream oxygen concentration vox, respectively.
Detect _n . Subsequently, in step 305, n is counted up. If necessary, step 30 is performed to adjust the timing of the catalyst deterioration determination.
It is also possible to provide a timing adjustment step after 4. Subsequently, in step 306, step 30
4 similarly to detect the catalyst upstream oxygen concentration Vabyf _n and catalyst downstream oxygen concentration vox _n.

Subsequently, at step 307, the catalyst temperature tc calculated at step 206 in FIG.
It reads at _n, in step 308, the reaction coefficients from the graph of FIG. 7 described above and the catalyst temperature TCAT _n Ma
Calculate p (tcat _n ). Subsequently, in step 309, in order to monitor how much the oxygen concentration changes between the upstream side and the downstream side of the catalyst device 5 within a predetermined period,
Catalyst upstream oxygen concentration change integrated value vabyfloc
_n (= | vabyf _n −vabyf _n−1 | × Map (t
_{cat n) + vabyfloc n-1} ) and the catalyst downstream oxygen concentration change amount integrated value voxloc _n (= | vox _n -v
ox _n-1 | × Map (tcat _n ) + voxlo
c _n-1 ). If necessary, step 30 is performed to adjust the timing of the catalyst deterioration determination.
It is also possible to provide a timing adjustment step after 9.

Subsequently, in step 310, it is determined whether or not n is larger than a predetermined value A. If n is larger than the predetermined value A, sufficient data is collected to determine the deterioration of the catalyst. And the process moves to step 311.
On the other hand, if n is equal to or smaller than the predetermined value A, it is determined that sufficient data for determining the deterioration of the catalyst has not been collected yet, and the process proceeds to step 305, and the above-described steps are repeated. In step 311, the ratio locr of the catalyst upstream oxygen concentration change amount vabyfloc _n to the catalyst downstream oxygen concentration change amount volocloc _n is calculated.

Subsequently, in step 312, it is determined whether or not the above-mentioned ratio locr is smaller than a predetermined value B.
If ocr is smaller than the predetermined value B, the necessary and sufficient oxidation reaction has been performed in the catalyst device 5, and it is determined that the catalyst has not deteriorated, and the routine proceeds to step 301, and the above steps are repeated. On the other hand, if the ratio locr is equal to or larger than the predetermined value B, it is determined that the necessary oxidation reaction has not been performed in the catalyst device 5 and the catalyst has been degraded.
Move to 3. In step 313, the driver is informed that the catalyst has deteriorated via the catalyst deterioration abnormality display unit 10, and the catalyst deterioration determination is terminated.

In addition to the above-described catalyst deterioration determination, the estimated catalyst initial temperature at the time of engine start accurately calculated by the estimated catalyst temperature calculation method of FIGS. 2 and 6, and the estimated catalyst from the engine start to the engine stop. A / F control using the temperature and the catalyst temperature as one parameter, the catalyst device 5
It is also possible to perform a sub feedback start determination or the like using the oxygen concentration sensor 7 (FIG. 1) on the downstream side of.

[0030]

According to the present invention, the catalyst temperature change from the stop of the internal combustion engine to the start of the next internal combustion engine is smaller than when the estimated catalyst temperature curve is set to be always convex downward. It is possible to accurately estimate, and therefore, it is possible to accurately estimate the catalyst initial temperature at the time of starting the engine.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a catalyst temperature estimation device for an internal combustion engine of the present invention.

FIG. 2 is a flowchart illustrating a catalyst initial temperature estimation method.

FIG. 3 is a graph showing a relationship between an elapsed time from an engine stop and an intake air temperature.

FIG. 4 is a water temperature model curve map including a plurality of water temperature curves.

FIG. 5 is an estimated catalyst temperature model curve map having a plurality of estimated catalyst temperature curves.

FIG. 6 is a flowchart illustrating a method for calculating an estimated catalyst temperature during engine operation.

FIG. 7 shows catalyst temperature tcat and reaction coefficient Map (tca).
6 is a graph showing a relationship with the graph of FIG.

FIG. 8 is a flowchart illustrating a catalyst deterioration determination method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 5 ... Catalyst device 11 ... ECU

Claims (1)

[Claims] 1. An estimated catalyst temperature curve is convex upward from a time when an internal combustion engine is stopped to a time when a predetermined time elapses, and the estimated catalyst temperature is from the time when the predetermined time elapses to a time when the estimated catalyst temperature reaches the outside air temperature. From the estimated catalyst temperature information in which the estimated catalyst temperature curve is convex downward, the estimated catalyst temperature when the internal combustion engine is stopped, and the elapsed time from when the internal combustion engine is stopped to when the internal combustion engine is started, the catalyst when the internal combustion engine is started is determined. A catalyst temperature estimation device for an internal combustion engine, which estimates an initial temperature.