JPH0783034A - Catalyst temperature control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To properly control catalyst temperature by providing a catalyst temperature control means which controls control parameters of an internal combustion engine so as to be lowered when a catalyst temperature is higher than a comparison temperature, and thereby preventing deterioration of the catalyst. CONSTITUTION:A branch pipe 7 is arranged on a downstream side of a throttle valve 3a of an intake pipe 2, while an absolute pressure sensor 8 is installed on a leading end of the branch pipe 7. An engine 1 is provided with an engine speed sensor 11 and a cylinder judgment sensor 12. A catalyst device 15 is arranged on the way of an exhaust pipe 14, for purifying poisonous components such as HC, CO, NOx included in exhaust gas. A catalyst temperature sensor 16 is arranged on a peripheral wall of the catalyst device 15 for supplying to an electronic control unit 5. Control parameters of the internal combustion engine 1 are controlled so as to be lowered when the catalyst temperature is higher than a comparison temperature. Proper catalyst temperature controlling is attained without affecting fuel consumption performance and operability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst temperature control device mounted on an exhaust system of an internal combustion engine to control the temperature of a catalyst for purifying harmful components in exhaust gas.

[0002]

2. Description of the Related Art Generally, in order to improve the exhaust gas purification performance of an internal combustion engine, the engine is equipped with an exhaust gas purification device,
We are trying to reduce the amount of harmful substances emitted from the engine. For example, a three-way catalyst device is used as an exhaust gas purification device, and in order to purify three components of CO, HC and NOx in the exhaust gas at the same time, according to the output value of an exhaust gas concentration detector arranged in the exhaust system of the engine. Feedback control is performed by the changing feedback control signal so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes the stoichiometric air-fuel ratio. In this way, the method of purifying the three-way catalyst by feedback-controlling the air-fuel ratio does not require the supply of secondary air and the purification efficiency of the three-way catalyst is good, but on the other hand, the three-way catalyst is used in the high-speed partial load operating range of the engine. If the temperature of (2) rises abnormally (for example, 800 ° C. or higher), the catalyst tends to deteriorate.

Therefore, the applicant of the present application filed Japanese Patent Application Laid-Open No. 4-298.
As disclosed in Japanese Patent No. 666, the catalyst temperature is a predetermined temperature (7
(00 ° C), the deterioration of the catalyst is prevented by controlling the control parameters of the internal combustion engine such as the air-fuel ratio supplied to the internal combustion engine, the ignition timing, and the exhaust gas recirculation amount (EGR) to lower the temperature of the catalyst. Proposing a device.

[0004]

However, in the conventional device for preventing the deterioration of the catalyst, the output of the temperature sensor may deviate from the actual temperature due to the inherent variation of the catalyst temperature sensor and the deterioration over time. If the deviation is in the positive direction, the catalyst temperature control will be inadvertently performed,
This causes deterioration of fuel efficiency and also affects drivability. Further, if the deviation is in the negative direction, the catalyst will be deteriorated without controlling the catalyst temperature even in a temperature range where the influence of the deterioration is high.

The present invention has been made in view of the above problems, and provides a catalyst temperature control device for an internal combustion engine capable of performing appropriate catalyst temperature control even if the output characteristics of the catalyst temperature sensor are deviated. With the goal.

[0006]

In order to achieve the above object, a catalyst temperature control device for an internal combustion engine according to the present invention is installed in an exhaust system of an internal combustion engine to purify harmful components in exhaust gas, and a catalyst for the catalyst. Catalyst temperature detecting means for detecting a temperature, and a catalyst for controlling a control parameter of the internal combustion engine so that the temperature of the catalyst becomes low when the temperature of the catalyst detected by the catalyst temperature detecting means exceeds a starting temperature. In a catalyst temperature control device for an internal combustion engine comprising a temperature suppressing means, when an operating state detecting means for detecting an operating state of the internal combustion engine, and an operating state detected by the operating state detecting means is a predetermined operating state Reference temperature storage means for storing the temperature of the catalyst detected by the catalyst temperature detection means as a reference temperature, and the reference temperature storage means for storing the reference temperature storage means. The predetermined value lower temperature than the reference temperature and a comparison temperature setting means for setting as a comparison temperature,
The catalyst temperature suppressing means controls the control parameter of the internal combustion engine so that the catalyst temperature becomes low when the catalyst temperature detected by the catalyst temperature detecting means is higher than the comparison temperature.

[0007]

The catalyst temperature control system for an internal combustion engine according to the present invention comprises:
The catalyst attached to the exhaust system of the internal combustion engine purifies harmful components in the exhaust gas, the temperature of the catalyst is detected by the catalyst temperature detecting means, and the temperature of the catalyst detected by the catalyst temperature detecting means is the start temperature. When exceeding, when controlling the control parameter of the internal combustion engine by the catalyst temperature suppressing means such that the temperature of the catalyst becomes low, the operating state of the internal combustion engine is detected by the operating state detecting means, and the detected operating state The temperature of the catalyst detected by the catalyst temperature detecting means when the is in a predetermined operating state is stored as a reference temperature by the reference temperature storage means, and a temperature lower than the reference temperature by a predetermined value is set as the comparison temperature by the comparison temperature setting means. When the catalyst temperature detected by the catalyst temperature detecting means is higher than the comparison temperature, the catalyst temperature suppressing means sets The control parameters of the combustion engine is controlled so that the catalyst temperature becomes lower.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a catalyst temperature control device for an internal combustion engine of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of an embodiment of a catalyst temperature control device for an internal combustion engine.

An internal combustion engine (hereinafter simply referred to as "engine") 1 is of a four cylinder type, and a throttle body 3 is provided in the middle of an intake pipe 2 connected to an intake port of each cylinder of the engine 1. , The throttle valve 3a inside
Are arranged. Further, a throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3a, and an electric signal corresponding to the opening of the throttle valve 3a is output to output an electronic control unit (hereinafter referred to as "ECU") 5 Supply to.

The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3a and slightly upstream of an intake valve (not shown) of the intake pipe 2. Further, each fuel injection valve 6 is connected to a fuel pump (not shown) and the ECU
The valve opening time of fuel injection is controlled by a signal from the ECU 5.

A branch pipe 7 is provided downstream of the throttle valve 3a of the intake pipe 2, and an absolute pressure (PBA) sensor 8 is attached to the tip of the branch pipe 7. The PBA sensor 8 is electrically connected to the ECU 5, and the intake pipe 2
The absolute pressure PBA therein is converted into an electric signal by the PBA sensor 8 and supplied to the ECU 5. An intake air temperature (TA) sensor 9 is attached to the wall of the intake pipe 2 downstream of the branch pipe 7, and the intake air temperature TA detected by the TA sensor 9 is converted into an electric signal and supplied to the ECU 5.

An engine water temperature (TW) sensor 10 composed of a thermistor or the like is attached to the cylinder peripheral wall filled with cooling water of the cylinder block of the engine 1, and the engine cooling water temperature TW detected by the TW sensor 10 is inserted. Is converted into an electric signal and supplied to the ECU 5. An engine speed (NE) sensor 11 and a cylinder discrimination (CYL) sensor 12 are mounted around a cam shaft or a crank shaft (not shown) of the engine 1. The NE sensor 11 is the engine 1
A signal pulse (hereinafter referred to as "TDC signal pulse") is output at a predetermined crank angle position every 180 degrees rotation of the crankshaft, and the CYL sensor 12 outputs a TDC signal pulse at a predetermined crank angle position of a specific cylinder. , Each of these T
The DC signal pulse is supplied to the ECU 5.

Further, the spark plug 13 of each cylinder of the engine 1 is electrically connected to the ECU 5, and the ECU 5 controls the ignition timing.

A catalyst device (three-way catalyst) 15 is provided in the middle of an exhaust pipe 14 connected to an exhaust port of the engine 1, and the catalyst device 15 allows HC and C in exhaust gas to be exhausted.
Purification of harmful components such as O and NOx is performed. On the peripheral wall of the catalyst device 15, a catalyst temperature (T
C) The sensor 16 is inserted, and the catalyst bed temperature TC detected by the TC sensor 16 is converted into an electric signal and the ECU 5
Is supplied to.

Further, an oxygen concentration sensor (hereinafter referred to as an O2 sensor) 17 is provided in the middle of the catalyst device 15, and the oxygen concentration in the exhaust gas detected by the O2 sensor 17 is converted into an electric signal. It is supplied to the ECU 5.

Further, an exhaust gas recirculation passage 18 is arranged between the intake pipe 2 and the exhaust pipe 14 in a bypass shape. One end of the exhaust gas recirculation passage 18 is connected to the exhaust pipe 14 on the upstream side (that is, the engine 1 side) of the O2 sensor 17,
The other end is connected to the intake pipe 2 upstream of the PBA sensor 8 (that is, on the throttle valve 3a side). Further, an exhaust gas recirculation amount control valve (hereinafter, referred to as EGR
A valve) 19 is installed. This EGR valve 19
Is a casing 22 composed of a valve chamber 20 and a diaphragm chamber 21, and a valve body 23 disposed in the valve chamber 20 and vertically movable so that the exhaust gas recirculation passage 18 can be opened and closed. And a diaphragm 25 connected to the valve element 23 via a valve shaft 24, and a spring 26 for urging the diaphragm 25 in the valve closing direction. The diaphragm chamber 21 includes an atmospheric pressure chamber 27 defined on the lower side and a negative pressure chamber 28 defined on the upper side via a diaphragm 25. That is, the atmospheric pressure chamber 27 is communicated with the atmosphere via the ventilation hole 27 a, while the negative pressure chamber 28 is connected to the negative pressure communication passage 29. Specifically, the negative pressure communication passage 29 is connected at its tip to the intake pipe 2 between the throttle valve 3 a and the other end of the exhaust gas recirculation passage 18, and the absolute pressure PBA in the intake pipe 2 passes through the negative pressure communication passage 29. It is adapted to be introduced into the negative pressure chamber 28 via the above. An atmosphere communication passage 30 is connected in the middle of the negative pressure communication passage 29, and a pressure adjusting valve 31 is provided in the middle of the atmosphere communication passage 30. The pressure adjusting valve 31 is a dual
The diaphragm chamber 21 is controlled by controlling the tee ratio.
The combined pressure introduced into the negative pressure chamber 28 is adjusted by a normally open solenoid valve.

When the pressure adjusting valve 31 is excited and closed,
The negative pressure in the negative pressure chamber 28 acting on the diaphragm 25 of the EGR valve 19 becomes large, the diaphragm 25 is displaced upward against the urging force of the spring 26, and the valve opening (lift amount) of the EGR valve 19 is increased. growing. On the other hand, the pressure control valve 31
When the valve is demagnetized and the valve is opened, the negative pressure in the negative pressure chamber 28 decreases, so that the diaphragm 25 is displaced downward by the biasing force of the spring 26, and the valve opening degree (lift amount) of the EGR valve 19 decreases. In this way, by energizing or demagnetizing the pressure regulating valve 31, the valve opening degree of the EGR valve 19 is controlled. Further, the pressure adjusting valve 31 is electrically connected to the ECU 5, and opens and closes in response to a command signal from the ECU 5,
The lift amount of the valve body 23 of the GR valve 19 and its lift operation speed are controlled.

Further, the EGR valve 19 is provided with a valve opening (lift) sensor (hereinafter referred to as L sensor) 32. The L sensor 32 indicates the operating position (lift amount) of the valve body 23 of the EGR valve. It detects and supplies the detection signal to ECU5.

Further, the ECU 5 shapes the input signal waveforms from the various sensors described above, corrects the voltage level to a predetermined level, converts the analog signal value into a digital signal value, and the like, and an input circuit 5a. Central arithmetic processing circuit (hereinafter referred to as "CPU") 5b and ROM for storing various arithmetic programs executed by the CPU 5b and predetermined maps
And a storage means 5c including a RAM for storing calculation results and the like.
And an output circuit 5d for supplying a drive signal to the fuel injection valve 6, the spark plug 13, and the pressure adjusting valve 31.

The ECU 5 (CPU 5b) discriminates various engine operating states such as an air-fuel ratio feedback control operating region and an open loop control operating region based on the above various engine operating parameter signals. The fuel injection time TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated based on the equation 1 according to the engine operating state.

[0021]

## EQU1 ## TOUT = Ti × K1 × KEGR × KO2 + K2 Here, Ti is a reference value of the fuel injection time TOUT of the fuel injection valve 6, and is determined according to the engine speed NE and the intake pipe absolute pressure PBA. . KEGR is a fuel amount correction coefficient, which corrects the fuel amount and controls the air-fuel ratio to the stoichiometric air-fuel ratio according to the variation of the exhaust gas recirculation passage 18 described later.

KO2 is an air-fuel ratio correction coefficient, which is set according to the oxygen concentration in the exhaust gas during the air-fuel ratio feedback control, that is, the output of the O2 sensor 17, and is not controlled by the feedback control. In the specific operation area (open-loop control operation area), it is set according to each operation area.

Further, the ECU 5 calculates the ignition advance value based on the equation 2 and controls the advance / retard of the ignition timing.

[0024]

[Mathematical formula-see original document] θIG = θIGMAP + θIGCAT where θIGMAP is the operating state of the engine, for example, NE-PBA-stored in the storage means 5c (ROM) in advance.
This is a basic ignition advance value set according to the engine speed NE and the intake pipe absolute pressure PBA based on the θIG map, and θIGCAT is applied when the catalyst bed temperature control is stored in advance in the storage means 5c (ROM). It is a correction ignition advance value set based on the correction value map.

In the above catalyst temperature control device, the ECU 5
Is the catalyst bed temperature TC detected by the TC sensor 16.
When the temperature exceeds the start temperature TSTART, the catalyst temperature suppressing means for controlling the control parameter of the internal combustion engine 1 to lower the catalyst bed temperature TC, and the TC sensor 16 when the detected operating state is a predetermined operating state. Reference temperature storage means for storing the detected catalyst bed temperature TC as a reference temperature is provided. Further, the ECU 5 uses the TC sensor 16
The exhaust gas recirculation amount increasing means for increasing the exhaust gas recirculation amount flowing through the exhaust gas recirculation passage 18 when the catalyst bed temperature TC detected by the exhaust gas recirculation amount is higher than the start temperature TSTART, and the exhaust gas recirculation amount increasing means increases the exhaust gas recirculation amount for a predetermined amount. Ignition timing correction means for advancing the ignition timing when the delay time T1 has elapsed,
When the exhaust gas recirculation amount is increased by the exhaust gas recirculation amount increasing means and a predetermined time T2 has passed, the catalyst bed temperature T
When C is lower than the start temperature TSTART but higher than the end temperature TEND, an air-fuel ratio enriching means for enriching the air-fuel ratio of the air-fuel mixture is provided. Further, the ECU 5 is provided with fuel amount correction means for correcting the fuel amount after a predetermined delay time T1 corresponding to the increase in the exhaust gas recirculation amount by the exhaust gas recirculation amount increasing means.

Next, a procedure for setting the starting temperature TSTART and the ending temperature TEND of the catalyst temperature control, which is the main point of this embodiment, will be described. FIG. 2 is a flowchart showing a catalyst temperature setting routine.

First, when this routine is started, a reference temperature monitor subroutine for detecting the reference temperature TREF of the catalyst bed temperature Tc is executed (step S1). FIG. 3 is a flowchart showing the reference temperature monitor subroutine.
First, it is determined whether the internal combustion engine is in the starting mode (step 201). In the start mode, the timer T4 is preset to count the time elapsed after the start and the countdown is started (step S202).
The timer T5 for measuring the duration of the predetermined operating state of the engine 1 is also preset to start the countdown (step S203), and the flag FOK for determining that the catalyst temperature control can be executed is set to the value "1". It sets (step S204) and returns to the main routine. When not in the start mode, it is determined whether or not a predetermined time T4 after the start has elapsed since the countdown was started after the timer T4 was preset (step S205). Until the predetermined time T4 after the start has elapsed, the timer T5 is preset to start the countdown again (step S203).
Return to the main routine. After a lapse of a predetermined time T4 after the start, it is determined whether or not the engine cooling water temperature TW is equal to or higher than the predetermined temperature Ta and the warm-up is completed (step S206). When the warm-up operation is not completed, the timer T5 starts the countdown after presetting again and returns to the main routine.

When the warm-up completion state is reached, it is determined whether or not the engine 1 has reached a predetermined operating state (step S207). When the predetermined operation state is not reached, the timer T5 is preset to start the countdown again. Here, the predetermined operating state is the engine speed N
e, a range set in the map of the absolute pressure PB in the intake pipe, and in the present embodiment, the catalyst bed temperature TC is a medium load operation range in which the catalyst bed temperature TC can reach a high temperature (for example, 800 ° C. or higher). When the engine 1 reaches the predetermined operating state, a predetermined time T5 is reached after the engine 1 reaches the predetermined operating state.
It is determined whether or not has passed (step S208).

When the predetermined time T5 has not elapsed, the value of the flag FOK is reset to "0" to interrupt the catalyst temperature control (step S209), preset the timer T6 and start down counting (step S210). ) Return to the main routine. When the predetermined time T5 has elapsed, it is determined whether or not the predetermined time T6 for calculating the average value of the catalyst bed temperature TC detected by the TC sensor 16 has elapsed (step S211). After the elapse of the predetermined time T5, the catalyst bed temperature TC rises to a temperature (for example, 800 ° C.) corresponding to the predetermined operation state. The catalyst bed temperature TC at that time is read until a predetermined time T6 elapses (step S212), and the average value of the read catalyst bed temperature TC is calculated (step S213). The calculation of this average value is performed by, for example, a weighted average according to Expression 3.

[0030]

## EQU3 ## TCAVE ← CTC / 100 × TC + (100−CTC) / 100 × TCAVE where CTC is an average smoothing coefficient set to any value between 0 and 100.

After calculating the average value, the process returns to the main routine. When the predetermined time T6 has passed, the flag FO
K is set to the value "1", the catalyst temperature control is restarted (step S214), and the process returns to the main routine.

Returning to the main routine of FIG. 2, step S
In step 2, it is determined whether or not the average value of the catalyst bed temperature Tc has been calculated. If it has been calculated, the process proceeds to the next processing step S3, but if it has not been calculated, this routine is once terminated.

The average value of the catalyst bed temperature TC calculated by the above-mentioned subroutine of FIG. 3 is stored in the storage means 5c of the ECU 5 as the reference temperature TREF of the catalyst bed temperature TC (step S3). Next, the constant temperature ΔT ₁ is subtracted from the reference temperature TREF stored in the storage means 5c based on the equation 4 to obtain the catalyst temperature control start temperature TSTART (step S4).

[0034]

## EQU4 ## T START = T REF −ΔT ₁ Here, in this embodiment, the constant temperature ΔT ₁ is 100 ° C.
Is set to. Therefore, since the reference temperature TREF is set to 800 ° C. in this embodiment, the catalyst temperature control start temperature TSTART becomes 700 ° C. Further, the end temperature TEND of the catalyst temperature control is set by adding hysteresis based on the start temperature TSTART, and in this embodiment, it is 650 ° C. which is lower than the start temperature TSTART by ΔT ₂ (= 50 ° C.) (step S5). ).

When the start temperature TSTART and the end temperature TEND are set, the catalyst temperature control will be executed according to the catalyst bed temperature Tc. The start determination routine will be described. FIG. 4 is a flowchart showing a catalyst temperature control start determination routine. First, step S204 and step S21 of the reference temperature monitor subroutine of FIG.
Flag F set in 4 and stored in the storage means 5c
It is determined whether OK is set to the value "1" (step S401). When the flag FOK is set to the value "1", the catalyst bed temperature TC is the start temperature TST.
Determine if ART or more (step S
402). When the flag FOK has the value "0", this routine is once terminated without doing anything thereafter. Further, when the catalyst bed temperature TC is equal to or higher than the start temperature TSTART, the catalyst temperature control is started and this routine is once ended (step S403). Catalyst bed temperature TC is start temperature TSTART
If the temperature has not yet reached, it is further determined whether or not the end temperature TEND has been reached (step S404). When the end temperature TEND is not reached, the catalyst temperature control is ended (step S405), and when the end temperature TEND is reached, this routine is once ended without ending the catalyst temperature control.

As described above, after the temperature control start temperature TSTART is set in the catalyst temperature setting routine, the catalyst temperature control is started when the start temperature TSTART is reached again.

Next, the catalyst temperature control is started by executing the catalyst temperature control by various means such as exhaust gas recirculation amount, ignition timing, air-fuel ratio, etc.
Since the catalyst temperature control is disclosed in detail in JP-A-298666, only its outline will be described here.

FIG. 5 is a time chart showing the operation timing of the various means incorporated in the ECU 5. ECU
5 reads the catalyst bed temperature TC output from the TC sensor 16, and when the catalyst bed temperature TC is higher than a start temperature TSTART at which catalyst deterioration occurs, for example, 700 ° C., a target valve of the EGR valve 19 by the exhaust gas recirculation amount increasing means. The opening degree value LCMD is increased to increase the exhaust gas recirculation amount (unburned gas) and decrease the catalyst bed temperature TC. After the elapse of a predetermined delay time T1, the fuel amount correction means calculates the fuel amount correction coefficient KEGR in order to correct the air-fuel ratio to the stoichiometric air-fuel ratio in response to the increase in the exhaust gas recirculation amount, and changes the fuel injection time TOUT. When the ignition timing correction means is executed at the same time as the fuel amount correction means is executed, the ignition timing θ
The ignition temperature is corrected to reduce the combustion temperature. When a predetermined time T2 when the air-fuel ratio A / F and the catalyst bed temperature TC are stabilized has elapsed and the catalyst bed temperature TC is higher than the end temperature TEND, the air-fuel ratio enriching means is executed to enrich the air-fuel ratio. The air-fuel ratio correction coefficient KO2 is increased to increase the air-fuel ratio to the rich side,
For example, the air-fuel ratio A / F = 14.3 is set.

As described above, according to the catalyst temperature control system for the internal combustion engine of this embodiment, the absolute value measured by the catalyst temperature sensor 16 is predetermined even if the sensor-specific variation or the time-dependent deterioration occurs. Since the start of the catalyst temperature control is decided based on the value relative to the average value of the reference temperature detected in the operating state, the catalyst is not deteriorated and the drivability is not affected, and the catalyst is controlled. It is possible to eliminate the above-described problems of the conventional catalyst temperature control without deterioration.

In the above embodiment, for example, the constant temperature ΔT is set to a predetermined temperature of 100 ° C.
You may set relatively according to the value of the signal output from a temperature sensor. The reference temperature TREF is the catalyst bed temperature TC.
Was set using the average value of the catalyst bed temperature TC measured within a predetermined time T6 after entering the predetermined operating state, but the present invention is not limited to this, and may be set to the maximum temperature within the predetermined time T6. Alternatively, various setting methods may be used, such as setting an average value of temperatures excluding the maximum temperature and the minimum temperature.

[0041]

According to the catalyst temperature control apparatus for an internal combustion engine of the present invention, even if there is a sensor-specific variation due to the absolute value of the catalyst temperature measured by the catalyst temperature detecting means or a deviation due to deterioration over time, Since the start of the catalyst temperature control is determined based on the value relative to the reference temperature, therefore, the appropriate catalyst temperature control can be performed without deteriorating the fuel efficiency and drivability and without degrading the catalyst. Can be performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an overall configuration of an internal combustion engine 1 incorporating an embodiment of a catalyst temperature control device of the present invention.

FIG. 2 is a flowchart showing a catalyst temperature setting routine.

FIG. 3 is a flowchart showing a reference temperature monitor subroutine.

FIG. 4 is a flowchart showing a catalyst temperature control start determination routine.

FIG. 5 is a time chart showing operation timings of various means.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... ECU 8 ... Absolute pressure sensor (operating state detecting means) 11 ... Engine speed sensor (operating state detecting means) 13 ... Spark plug 16 ... Catalyst temperature sensor (catalyst temperature detecting means) 17 ... Oxygen concentration sensor 19 ... EGR valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location F02D 43/00 BE

Claims (3)

[Claims] 1. A catalyst attached to an exhaust system of an internal combustion engine for purifying harmful components in exhaust gas, catalyst temperature detecting means for detecting the temperature of the catalyst, and temperature of the catalyst detected by the catalyst temperature detecting means. When the temperature exceeds a starting temperature, a catalyst temperature control device for an internal combustion engine, comprising: a catalyst temperature suppressing means for controlling the control parameter of the internal combustion engine so that the temperature of the catalyst becomes low; Operating state detecting means for detecting, and reference temperature storing means for storing the temperature of the catalyst detected by the catalyst temperature detecting means as a reference temperature when the operating state detected by the operating state detecting means is a predetermined operating state. And a comparison temperature setting means for setting a temperature lower than the reference temperature stored in the reference temperature storage means by a predetermined value as a comparison temperature. The catalyst temperature suppressing means controls the control parameter of the internal combustion engine so that the catalyst temperature becomes low when the catalyst temperature detected by the catalyst temperature detecting means is higher than the comparison temperature. Catalyst temperature controller. 2. The catalyst temperature control device for an internal combustion engine according to claim 1, wherein the operating parameter is at least one of ignition timing, air-fuel ratio, and exhaust gas recirculation amount. 3. The internal combustion engine according to claim 1, wherein the predetermined operation state is a time when a predetermined time has elapsed after the start of the internal combustion engine and the internal combustion engine continues in a medium load operation state. Catalyst temperature controller.