JP2001021524A - Simulated temperature calculation device of exhaust system part of internal combustion engine and electric heater control device of air-fuel ratio sensor for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the temperature of exhaust system parts of an internal combustion engine, accurately and simply. SOLUTION: An oxygen sensor 31 is arranged inside an engine exhaust passage, and a water-temperature sensor 28 for detecting the engine cooling-water temperature is installed on an engine body 1. The initial value of a sensor simulated temperature showing the temperature of the oxygen sensor 31 is set corresponding to the engine cooling-water temperature. The temperature is renewed successively corresponding to the engine operation state from the initial value, to calculate the sensor simulated temperature. By this method, if the sensor simulated temperature is lower than a heater operation temperature, an electric heater 41 of the oxygen sensor 31 is operated, and if the sensor simulated temperature is higher than a heater stopping temperature, the electric heater 41 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for calculating a simulated temperature of exhaust system components of an internal combustion engine and an electric heater control device for an air-fuel ratio sensor for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, there has been known an internal combustion engine in which an electric heater is attached to an air-fuel ratio sensor, for example, an oxygen sensor disposed in an engine exhaust passage. Generally, if the temperature of the oxygen sensor is lower than its activation temperature, the oxygen sensor cannot accurately detect the air-fuel ratio. Therefore, in this internal combustion engine, the temperature of the oxygen sensor is maintained higher than its activation temperature by the electric heater.

However, if the electric heater is operated when the temperature of the oxygen sensor is sufficiently high, for example, after a high engine load operation has been continued for a long time, or during a warm restart, the oxygen sensor is activated. Risk of overheating. Therefore, it is necessary to know the temperature of the oxygen sensor in order to operate the electric heater properly. Therefore, there is known an internal combustion engine in which a temperature sensor is attached to an oxygen sensor to detect the temperature of the oxygen sensor (see Japanese Patent Application Laid-Open No. 5-202785).

[0004]

However, this internal combustion engine has a problem that not only a device for processing an output signal from the temperature sensor is required but also the cost is increased. Accordingly, an object of the present invention is to provide an apparatus capable of accurately and easily obtaining the temperature of an exhaust system component of an internal combustion engine. It is another object of the present invention to provide an electric heater control device capable of preventing the air-fuel ratio sensor from being overheated while maintaining the air-fuel ratio sensor in an active state.

[0005]

According to a first aspect of the present invention, an initial value of a simulated temperature representing a temperature of an exhaust system component of an internal combustion engine is set according to an engine cooling water temperature. The simulated temperature is calculated by sequentially updating the values in accordance with the engine operating state. That is, 1
According to the second aspect, the simulated temperature representing the temperature of the exhaust system component is easily and accurately calculated.

A second aspect of the present invention is the air-fuel ratio sensor according to the first aspect, wherein the exhaust system component is disposed in an engine exhaust passage. That is, in the second aspect, the simulated temperature representing the temperature of the air-fuel ratio sensor is calculated. According to a third aspect of the present invention, an initial value of the simulated temperature representing the temperature of the air-fuel ratio sensor of the internal combustion engine is set according to the engine cooling water temperature, and the initial value is set according to the engine operating state. The simulated temperature is calculated by successively updating the simulated temperature, and when the simulated temperature is lower than a predetermined set temperature, the electric heater of the air-fuel ratio sensor is activated, and when the simulated temperature is higher than the set temperature, the electric heater is stopped. I have to. That is, in the third aspect, since the appropriate operation of the electric heater is ensured, overheating of the air-fuel ratio sensor is prevented while maintaining the air-fuel ratio sensor in the active state.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is an engine body, 2 is a piston, 3 is a combustion chamber, 4 is an intake port, 5 is an intake valve, 6 is an exhaust port, 7 is an exhaust valve, and 8 is ignition. The plugs are each shown. The intake port 4 is connected to a surge tank 10 via a corresponding intake branch 9, and the surge tank 10 is connected to an air cleaner 12 via an intake duct 11. A fuel injection valve 13 is arranged in the intake branch pipe 9, and the intake duct 1
The throttle valve 14 is disposed in the inside of the valve 1. On the other hand, the exhaust port 6 is connected to a catalytic converter 17 via an exhaust manifold 15 and an exhaust pipe 16, and the catalytic converter 17 is connected to an exhaust pipe 18.

An electronic control unit (ECU) 20 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 22 and R via a bidirectional bus 21.
AM (random access memory) 23, CPU (microprocessor) 24, BR constantly connected to power supply
An AM (backup RAM) 25, an input port 26, and an output port 27 are provided. A water temperature sensor 2 for generating an output voltage indicating the engine cooling water temperature THW is provided on the engine body 1.
A mass flow sensor or an air flow meter 29 for generating an output voltage indicating the intake air mass flow Ga is attached to the intake duct 11 upstream of the throttle valve 14. Air-fuel ratio sensors 30 and 31 for generating output signals indicating the air-fuel ratio are attached to the exhaust pipe 16 upstream of the catalytic converter 17 and the exhaust pipe 18 downstream of the catalytic converter 17, respectively. The output voltages of these sensors 28, 29, 30, 31 are input to the input port 26 via the corresponding AD converters 32, respectively. Further, a rotation speed sensor 33 that generates an output pulse representing the engine rotation speed N is provided at the input port 26,
And a vehicle speed sensor 34 for generating an output pulse representing the vehicle speed SPD. On the other hand, the output port 27 is connected to each ignition plug 8 and each fuel injection valve 13 via a corresponding drive circuit 35.

In the internal combustion engine shown in FIG. 1, the fuel injection amount is controlled based on the output signals of the air-fuel ratio sensors 30 and 31 so that the air-fuel ratio becomes the target air-fuel ratio. For example, when the catalytic converter 17 includes a three-way catalyst, the target air-fuel ratio is set to the stoichiometric air-fuel ratio. In this case, the air-fuel ratio sensors 30 and 31 are formed from oxygen sensors whose output voltage changes according to the oxygen concentration in the exhaust gas.
Is called an oxygen sensor. In the present embodiment, the oxygen sensor 30 upstream of the catalytic converter 17 is a sensor that generates an output voltage substantially proportional to the air-fuel ratio. On the other hand, the oxygen sensor 31 downstream of the catalytic converter 17 is a sensor whose output voltage changes stepwise near the stoichiometric air-fuel ratio. As shown in FIG. 1, electric heaters 40 and 41 are attached to the oxygen sensors 30 and 31, respectively, and these electric heaters 40 and 41 are connected to the output port 27 via a corresponding drive circuit 35. . Next, the catalytic converter 17
A method for controlling the electric heater 41 of the downstream oxygen sensor 31 will be described. The electric heater 40 of the oxygen sensor 30 upstream of the catalytic converter 17 can be controlled in the same manner.

As described at the beginning, it is necessary to know the temperature of the oxygen sensor 31 in order to operate the electric heater 41 properly. If a temperature sensor is attached to the oxygen sensor 31, the temperature of the oxygen sensor 31 can be known, but this is not preferable. Therefore, in this embodiment, a sensor simulated temperature TS representing the temperature of the oxygen sensor 31 is calculated, and the operation and stop of the electric heater 41 are controlled according to the sensor simulated temperature TS.

That is, referring to the control routine of the electric heater 41 shown in FIG. 2, first, at step 100, it is determined whether or not the electric heater 41 is currently operated (ON). When the electric heater 41 is currently stopped (OFF), the routine proceeds to step 101, where it is determined whether or not the sensor simulated temperature TS is lower than a predetermined heater operating temperature THON. When TS <THON, the process proceeds to step 102, where the electric heater 41 is operated. On the other hand, when TS ≧ THON, the processing cycle ends, that is, the electric heater 41 is kept stopped. On the other hand, in step 100, the current electric heater 4
When 1 is operated, the routine then proceeds to step 103, where it is determined whether or not the sensor simulated temperature TS is higher than a heater stop temperature THOFF which is higher than the heater operation temperature THON. When TS> THOFF, the routine proceeds to step 104, where the electric heater 41 is stopped. On the other hand, when TS ≦ THOFF, the processing cycle ends, that is, the electric heater 41 is maintained in the operating state. This routine is executed by interruption every predetermined set time.

In this manner, the oxygen sensor 31 can be maintained in an active state while preventing the oxygen sensor 31 from being overheated. Next, a method of calculating the sensor simulated temperature TS will be described. In this embodiment, every time the engine is started, an initial value TINT of the sensor simulated temperature TS is set according to the engine cooling water temperature THW, and the sensor simulated temperature is updated by sequentially updating the initial value TINT according to the engine operating state. The TS is calculated. That is, the sensor simulated temperature TS is calculated based on, for example, the following equation.

TS (i) = TS (i−1) + (STS−TS (i−1)) / m (i = 1, 2,...) (1) where TS (i) is the i-th time In the update, the sensor simulated temperature, STS represents the sensor steady temperature, and m represents the smoothing coefficient. The sensor steady temperature STS is an oxygen sensor 3 obtained when the current engine operating state is assumed to be steady.
1, which is calculated based on the following equation.

STS = STSB + KR-KS Here, STSB represents the basic sensor steady-state temperature, KR represents an ignition retard correction coefficient, and KS represents a traveling wind correction coefficient. Assuming that the engine load L is represented by the ratio of the intake air mass flow rate (for example, g / rev) detected by the air flow meter 29 to the maximum intake air mass flow rate of the engine 1, the basic sensor steady temperature STSB is equal to the engine load L and the engine load. This is a sensor steady temperature determined according to the rotation speed N, and is obtained in advance by an experiment. The basic sensor steady temperature STSB is stored in the ROM 22 in advance in the form of a map shown in FIG. 3 as a function of the engine load L and the engine speed N.

The ignition retard correction coefficient KR is used to correct the basic sensor steady-state temperature STSB based on an increase in the combustion temperature or the exhaust temperature obtained when the ignition timing is retarded, and is determined in advance by an experiment. Have been. The ignition retard correction coefficient KR is stored in advance in the ROM 22 in the form of a map shown in FIG. 4 as a function of the intake air mass flow rate Ga and the ignition timing retard amount RTD.

The traveling wind correction coefficient KS is used to correct the basic sensor steady temperature STSB based on the amount of cooling by the traveling wind of the vehicle, and is obtained in advance by experiments. The traveling wind correction coefficient KS increases as the vehicle speed SPD increases, and is stored in the ROM 22 in advance in the form of a map shown in FIG. 5 as a function of the vehicle speed SPD. On the other hand, the smoothing coefficient m represents the number of updates required from when the engine load changes until the sensor simulated temperature TS matches the sensor steady-state temperature STS, and is calculated based on, for example, the following equation.

M = KTM / PRD Here, KTM represents an annealing time constant, and PRD represents an update time interval of the sensor simulated temperature TS. The smoothing time constant KTM is determined by the actual oxygen sensor 3 after the engine load changes.
It indicates the time required until the temperature of 1 becomes steady or converges, and is obtained in advance by experiments. The annealing time constant KTM decreases as the intake air mass flow rate Ga increases, and is stored in advance in the ROM 22 in the form of a map shown in FIG. 6 as a function of the intake air mass flow rate Ga.

Therefore, referring again to equation (1), the current sensor steady temperature STS and the previous sensor simulated temperature TS (i
-1) and the difference (STS-TS (i-1))) divided by the smoothing coefficient m, and the previous sensor simulated temperature TS (i-
By adding to (1), the sensor simulated temperature TS is updated. TS (0) when i = 1 in Expression (1) corresponds to the initial value TINT of the sensor simulated temperature TS. Next, a method of calculating the initial value TINT will be described.

If the amount of change or decrease DTS in the sensor temperature from when the engine is stopped to when the engine is started can be determined, the sensor temperature at the time when the engine is started, that is, the initial value TINT can be determined accurately. Can be.
However, the sensor temperature change amount DTS is a difference DTHW (THWO) between the engine cooling water temperature THWOLD when the engine is stopped and the engine cooling water temperature THW when the engine is started.
LD-THW) and the sensor simulated temperature TSOLD when the engine is stopped. That is, the sensor temperature change amount DTS is equal to the cooling water temperature difference DT as shown in FIG.
It increases as HW increases, and increases as TSOLD increases. The sensor simulated temperature change amount DTS is stored in the ROM 22 in advance in the form of a map shown in FIG. Therefore, the initial value TINT can be calculated by subtracting the sensor simulated temperature change amount DTS from TSOLD (TINT = TSOLD-DT).
S).

Therefore, generally speaking, every time the engine is started, it is determined based on the engine cooling water temperature and the sensor simulated temperature when the engine was last stopped, and the engine cooling water temperature when the engine was started. This means that the initial value TINT has been calculated. By the way, every time the engine is started, the initial value TI
It is considered that the sensor simulated temperature can be obtained by successively updating even if NT is set to a constant value. In this case, if this constant value is set lower than the heater operating temperature THON (see FIG. 2), the electric heater 41 is always activated when the engine is started, and the temperature of the oxygen sensor 31 is high as in the restart immediately after the engine is stopped. Sometimes oxygen sensor 31
May be overheated. Even if the constant value is set to a value slightly higher than the heater operating temperature THON, the temperature may become lower than the heater operating temperature THON regardless of the actual temperature of the oxygen sensor 31 in the process of updating the sensor simulated temperature TS. is there. Therefore, when setting the initial value TINT to a constant value, it is preferable to set the initial value TINT to a value extremely higher than the heater operating temperature THON. However, in this case, the sensor simulated temperature becomes the heater operating temperature THON.
It takes a long time for the temperature to become lower than this. During this time, the electric heater 41 is not operated, so that the oxygen sensor 31 cannot be quickly activated.

On the other hand, in this embodiment, since the initial value TINT is determined according to the engine cooling water temperature THW as described above, the sensor simulated temperature TS and the actual oxygen sensor 31 are used.
And the deviation from the temperature can be kept small. Therefore, the oxygen sensor 31 can be quickly brought into the active state while preventing the oxygen sensor 31 from being overheated, especially immediately after the engine is started.

Further, in the internal combustion engine shown in FIG. 1, when the simulated sensor temperature TS becomes higher than the threshold value, the fuel injection amount is increased from that in the normal operation to lower the combustion temperature or the exhaust gas temperature. An overheating prevention increase is performed to prevent the overheating of the base 31. Next, the control of the overheating prevention increase will be described with reference to the routine of FIG.

Referring to the routine of FIG. 8, first, at step 200, it is determined whether or not the increase flag XINC is set. This increase flag XINC is set when the overheat prevention increase is to be performed (XINC =
"1"), which is reset when the overheat prevention increase should be stopped (XINC = "0"). Increase flag XI
If the NC has been reset, then step 20
1 and the sensor simulated temperature TS becomes the increase start temperature TION
Is determined. When TS ≦ TION, the processing cycle ends, and when TS> TION, the routine proceeds to step 202, where the increase flag XINC is set. That is, the overheating prevention increase is started.

On the other hand, if the increase flag XINC is set in step 200, then step 2
03, the sensor steady-state temperature STS becomes the increase stop temperature TI.
It is determined whether it is lower than OFF. STS ≧ TIO
When FF, the processing cycle ends, and STS <TIO
In the case of FF, the routine proceeds to step 204, where the increase flag XINC is reset. That is, the overheat prevention increase is stopped. This routine is executed by interruption every predetermined set time.

By the way, while the overheating prevention increase is being performed, the actual simulated time constant deviates from the KTM shown in FIG. 6, so that the sensor simulated temperature TS cannot be accurately obtained at this time. Therefore, in the present embodiment, the update of the sensor simulated temperature TS is stopped while the overheating prevention increase is performed, and the sensor simulated temperature TS is maintained at a constant value, for example, an increase start temperature TION. By doing so, the overheat prevention increase is stopped and the sensor simulated temperature TS
The sensor simulated temperature TS can be accurately obtained even after the renewal of is updated. Further, in step 203 where the sensor simulated temperature TS is held at the increase start temperature TION, the sensor steady temperature STS schematically representing the temperature of the oxygen sensor 31 is used instead of the sensor simulated temperature TS. The increase can be stopped appropriately.

FIGS. 9 and 10 show a routine for calculating the simulated sensor temperature TS according to this embodiment. This routine is executed by interruption every predetermined time PRD. Note that TS and TSOL in this routine
D corresponds to TS (i) and TS (i-1) in equation (1). Referring to FIGS. 9 and 10, first, at step 300, the basic sensor steady temperature STSB is calculated from the map of FIG. In the following step 301, the ignition retard correction coefficient KR is calculated from the map of FIG. In the following step 302, the traveling wind correction coefficient KS is calculated from the map of FIG. In the following step 303, the sensor steady temperature STS
Is calculated (STS = STSB + KR-KS). In the following step 304, it is determined whether or not the increase flag XINC has been reset. When the increase flag XINC is reset, the process proceeds to step 305, and
It is determined whether the process has proceeded to step 305 for the first time after the start of the engine. When the process proceeds to step 305 for the first time after the start of the engine, that is, when the initial value TINT has not yet been calculated, then steps 306 and 3 are executed.
07, otherwise jump to step 308. In step 306, a routine for calculating the initial value TINT is executed. This routine is shown in FIG.

Referring to FIG. 11, first, at step 400,
The engine cooling water temperature THWO when the engine was stopped last time
Cooling water temperature difference DT from LD and current engine cooling water temperature THW
HW is calculated (DTHW = THWOLD-TH
W). In the following step 401, the sensor simulated temperature change amount D
TS is calculated from the map of FIG. Next step 40
At 2, the sensor simulated temperature TS when the engine was stopped last time
Initial value TI from OLD and sensor simulated temperature change amount DTS
NT is calculated (TINT = TSOLD-DTS).
In the following step 403, the initial value TINT is set to the maximum allowable value M.
It is determined whether it is larger than AX. TINT ≦ MA
If X, then the process proceeds to step 405, where TINT>
In the case of MAX, the process proceeds to step 405 after setting the initial value TINT to the maximum allowable value MAX. In step 405, it is determined whether the initial value TINT is smaller than the allowable minimum value MIN. When TINT ≧ MIN, the processing cycle is terminated, and when TINT <MIN, the initial value T
After setting INT to the minimum allowable value MIN, the processing cycle ends.

Referring again to FIGS. 9 and 10, in the following step 307, the initial value TINT is set to the sensor simulated temperature TS.
Is stored as In the following step 308, it is determined whether or not a predetermined time, for example, a few seconds, has elapsed since the engine was started. If the fixed time has not elapsed since the start of the engine, the process jumps to step 312.
That is, immediately after the start of the engine, not only the engine operation but also the output of each sensor is not stable.
S is not updated. On the other hand, when the predetermined time has elapsed, the process then proceeds to step 309,
The annealing time constant KTM is calculated from the map of FIG. In the following step 310, a smoothing coefficient is calculated (M = K
MT / PRD). In the following step 311, the sensor simulated temperature TS is updated using the following equation.

TS = TSOLD + (STS−TSOLD) / m In the following step 312, the current sensor simulated temperature TS is T
The current engine cooling water temperature THW is stored as THWOLD. Therefore, after the engine is started, TSOLD and T
HWOLD represents the sensor simulated temperature and the engine cooling water temperature when the engine was stopped last time.

On the other hand, if the increase flag XINC is set in step 304, then step 3
13 and the sensor simulated temperature TS becomes the heater operating temperature TI
It is kept ON. In the embodiments described so far,
The case where the present invention is applied to the case where the simulated temperature of the oxygen sensor 31 downstream of the catalytic converter 17 is obtained is shown. However, the oxygen sensor 30 upstream of the catalytic converter 17,
The present invention can be applied to the case where the temperatures of a catalyst, an exhaust manifold, an exhaust pipe, and the like are obtained. Further, the electric heater 4 of the oxygen sensor 30 upstream of the catalytic converter 17
The present invention can also be applied to the case of controlling the operation or stop of the electric heater attached to 0 or the catalyst.

[0031]

The temperature of the exhaust system components of the internal combustion engine can be accurately and easily obtained.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a flowchart showing a control routine of the electric heater.

FIG. 3 is a diagram showing a basic sensor steady temperature STSB.

FIG. 4 is a diagram showing an ignition retard correction coefficient KR.

FIG. 5 is a diagram showing a traveling wind correction coefficient KS.

FIG. 6 is a diagram showing an average time constant KTM.

FIG. 7 is a diagram showing a sensor simulated temperature change amount DTS.

FIG. 8 is a flowchart showing a control routine for increasing the amount of overheating prevention.

FIG. 9 is a flowchart illustrating a routine for calculating a sensor simulated temperature TS.

FIG. 10 is a flowchart illustrating a calculation routine of a sensor simulated temperature TS.

FIG. 11 is a flowchart illustrating a routine for calculating an initial value TINT.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine body 15 ... Exhaust manifold 17 ... Catalytic converter 31 ... Oxygen sensor 28 ... Water temperature sensor 41 ... Electric heater

Claims (3)

[Claims] An simulated temperature is calculated by setting an initial value of a simulated temperature representing the temperature of an exhaust system component of an internal combustion engine in accordance with an engine cooling water temperature and sequentially updating the simulated temperature in accordance with an engine operating state. A simulated temperature calculating device for an exhaust system component of an internal combustion engine. 2. The simulated temperature calculating device for an exhaust system component of an internal combustion engine according to claim 1, wherein the exhaust system component is an air-fuel ratio sensor disposed in an engine exhaust passage. 3. The simulated temperature is calculated by setting an initial value of a simulated temperature representing the temperature of an air-fuel ratio sensor of the internal combustion engine in accordance with the engine cooling water temperature, and sequentially updating the simulated temperature in accordance with the engine operating state. When the simulated temperature is lower than a predetermined set temperature, the electric heater of the air-fuel ratio sensor is operated, and when the simulated temperature is higher than the set temperature, the electric heater is stopped. Electric heater control device for fuel ratio sensor.