JP2013234573A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently reduce manufacturing costs required for preventing damage to an exhaust gas sensor by eliminating the need for instruments or the like employed for measuring the amount of condensation water accumulated in an exhaust pipe and allow reduction of exhaust gas by activating the exhaust gas sensor as early as possible.SOLUTION: An exhaust pipe wall temperature estimation part calculates an estimated wall temperature in an exhaust pipe which is determined one by one from an exhaust temperature detected from an exhaust temperature sensor, the flow rate of gas detected from an air flow meter, and an outside air temperature detected by an outside air temperature sensor by referring to a map for calculating the supplied amount of heat, a wall temperature additional value map, and a wall temperature subtraction value map. Then a dew-point temperature calculation part of an exhaust pipe wall calculates, by referring to a dew-point temperature calculation map, the dew-point temperature determined from an air-fuel ratio between the flow rate of gas and the weight of fuel. A condensation water amount estimation part determines a relative wall temperature from the estimated wall temperature and the dew-point temperature by referring to a map for calculating a condensation water accumulated amount, calculates the condensation water accumulated amount from the relative wall temperature and the flow rate of gas, and estimates a value obtained by totalizing a calculated condensation water accumulated amount as the amount of the condensation water.

Description

  The present invention relates to a control device for an internal combustion engine having a function of estimating the amount of condensed water generated in an exhaust pipe of the internal combustion engine.

  In general, the exhaust gas of an internal combustion engine contains water vapor generated by the combustion reaction of fuel and intake air. When the exhaust gas containing water vapor is cooled in the exhaust pipe, the exhaust gas in the exhaust pipe contains Water vapor condenses to produce condensed water. However, when the oxygen sensor arranged in the exhaust pipe is heated by the heater, if the condensed water generated in the exhaust pipe adheres to the high-temperature oxygen sensor, the sensor element may be broken.

  As a countermeasure, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-316594), a temperature sensor is disposed outside the exhaust pipe, and the temperature of the exhaust pipe is estimated by the temperature sensor. Based on the temperature, it is determined whether or not condensate can exist in the exhaust pipe. If the condensate can exist, the exhaust pipe is heated by a heat medium heated by the combustion burner. There is what I did.

JP 2004-316594 A

  In order to achieve the above object, in the control apparatus for a conventional internal combustion engine as described above, in the exhaust system of the internal combustion engine, temperature acquisition means is provided outside the exhaust pipe, and temperature acquisition means provided outside is provided. Thus, the temperature of the exhaust pipe is acquired, and the generation of condensed water in the exhaust pipe is prevented based on the temperature.

  More specifically, an exhaust pipe of the internal combustion engine, an exhaust gas sensor that detects the oxygen concentration of the exhaust gas by a sensor element that is activated when heated, a sensor element heating means that heats and activates the sensor element, Temperature acquisition means that is disposed outside the exhaust pipe and acquires the temperature of the exhaust pipe, and condensed water status determination means that determines the status of the condensed water upstream of the exhaust gas sensor based on the acquired temperature of the exhaust pipe And it is necessary to newly provide an exhaust pipe heating means for heating the exhaust pipe upstream of the exhaust gas sensor when it is determined that condensate can exist upstream of the exhaust gas sensor. There was a problem that the manufacturing cost of a minute would be borne.

  The present invention has been made to solve the above-described conventional problems, and eliminates the need for an instrument for measuring the amount of condensed water accumulated in the exhaust pipe, thereby sufficiently increasing the manufacturing cost for preventing damage to the exhaust gas sensor. An object of the present invention is to provide a control device for an exhaust gas sensor that can be reduced to a low level.

  In order to achieve the above object, the exhaust gas sensor control apparatus according to the present invention is (1) an exhaust gas sensor control apparatus for controlling an energization state of a heater for heating an exhaust gas sensor provided in an exhaust pipe of an internal combustion engine. Exhaust temperature detection means for detecting the exhaust temperature of the exhaust gas from the pipe, gas flow rate detection means for detecting the flow rate of the gas sucked into the internal combustion engine, outside air temperature detection means for detecting the outside air temperature, and the internal combustion engine Condensed water that accumulates in the exhaust pipe using the exhaust temperature detected by the exhaust temperature detection means, the gas flow rate detected by the gas flow detection means, and the outside air temperature detected by the outside air temperature detection means when the engine is started The amount of condensed water is estimated, and when the condensed water is determined to be equal to or less than a predetermined value by the condensed water amount estimating means, energization of the heater is permitted. And heating control means for cormorants control, configured with a.

  This configuration generally estimates the amount of condensed water that accumulates in the exhaust pipe using the exhaust temperature, gas flow rate, and outside air temperature when the internal combustion engine is started, and generally determines the estimated amount of condensed water. Condensed water collected in the exhaust pipe is used to heat the heater when it is determined that the condensed water is below a predetermined value using output values from the exhaust temperature sensor, air flow meter, and outside air temperature sensor provided in the internal combustion engine. It is possible to reduce the manufacturing cost required for preventing damage to the exhaust gas sensor by eliminating the need for an instrument for measuring the amount.

  In the exhaust gas sensor control apparatus according to (1) above, (2) the condensed water amount estimation means calculates an estimated wall temperature in the exhaust pipe that is sequentially obtained using the exhaust temperature, the gas flow rate, and the outside air temperature. And calculating a dew point temperature of the exhaust pipe obtained from an air-fuel ratio of the gas flow rate and fuel weight, obtaining a relative wall temperature from the calculated estimated wall temperature and dew point temperature, and calculating the relative wall temperature and the gas flow rate. The condensed water integrated amount is calculated from the value, and the value obtained by integrating the calculated condensed water integrated amount is estimated as the amount of condensed water.

  With this configuration, the estimated wall temperature in the exhaust pipe, which is obtained sequentially using the exhaust temperature, gas flow rate, and outside air temperature, is calculated, and the dew point temperature of the exhaust pipe is calculated from the air-fuel ratio of the gas flow rate and fuel weight. The relative wall temperature is obtained from the estimated wall temperature and dew point temperature, the condensed water integrated amount is calculated from the relative wall temperature and the gas flow rate, and the value obtained by integrating the calculated condensed water integrated amount is used as the amount of condensed water. By estimating, the output values from the air flow meter, exhaust temperature sensor, and outside air temperature sensor that are generally provided in internal combustion engines are used, eliminating the need for equipment that measures the amount of condensed water that accumulates in the exhaust pipe. Thus, the manufacturing cost for preventing damage to the exhaust gas sensor can be sufficiently reduced.

  In the exhaust gas sensor control apparatus according to (1) or (2), (3) the condensed water amount estimating means estimates the amount of condensed water upstream and downstream of the exhaust gas sensor accumulated in the exhaust pipe. Configure to

  With this configuration, in order to estimate the amount of condensed water upstream and downstream of the exhaust gas sensor that accumulates in the exhaust pipe, the amount of condensed water is larger than when estimating the amount of condensed water upstream or downstream. Since the determination accuracy can be further increased and the heater of the exhaust gas sensor is further heated, it is possible to reliably prevent the exhaust gas sensor from being damaged.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus of the internal combustion engine which fully reduces the manufacturing cost concerning the damage prevention of an exhaust gas sensor can be provided, the instrument etc. which measure the quantity of the condensed water which accumulates in an exhaust pipe are unnecessary.

System Configuration. Control configuration of the engine control device. Exhaust sensor structure. Exhaust sensor control configuration. Elapsed time after startup and element temperature. Condensate estimation method during engine operation. Condensate estimation method when the engine is stopped. Heater energization method. Heater energization method. Heater energization method. Setting method of heater energization timing. Setting method of heater energization timing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an internal combustion engine provided with an exhaust gas sensor with a heater to which a control device according to the present invention is applied.

  In the illustrated internal combustion engine 100, a spark plug 102 to which an ignition voltage is applied from an ignition coil 103 is disposed at the head (combustion chamber) of a cylinder 107 in which a water temperature sensor 110 is disposed. In connection with the valve operating mechanism, a crank angle sensor 111 and a cam angle sensor 112 are provided, and an intake system (intake pipe 108) includes a fuel injection valve 101, a throttle valve 104, a throttle position sensor 113, an intake pipe pressure sensor 114, An intake air flow meter 115, an intake air temperature sensor 121, and the like are provided, and the exhaust air system (exhaust pipe 109) includes the linear air-fuel ratio sensor 10, the exhaust gas temperature sensor 122, the catalyst 118, and the like shown in FIG. Has been. Fuel that has been regulated to a constant pressure is pumped from the fuel tank 125 through the fuel pump 117 and the fuel pressure control valve 126 to the fuel injection valve 101.

  And in the control apparatus 1 of this embodiment, control of the temperature (heat generation amount) of the heater 30 (refer FIG. 3A) for the detection element heating provided in the said linear air fuel ratio sensor 10, and the fuel by the said fuel injection valve 101 A control unit 120 is provided to control the injection amount and fuel injection timing, control the ignition timing of the spark plug 102, and the like.

  As shown in FIG. 2, the control unit 120 includes a CPU 401 that performs numerical and logical operations, a ROM 402 that stores programs and data executed by the CPU 401, a RAM 403 that temporarily stores data, and analog signals from each sensor. An A / D converter 404 that captures and converts it into a digital signal, a digital input circuit 405 that captures signals from switches indicating operation states, a pulse input circuit 406 that counts the time interval of pulse signals and the number of pulses within a predetermined time, Furthermore, a digital output circuit 407, a pulse output circuit 408, and a communication circuit 409 are provided to turn ON / OFF an actuator (not shown) based on the calculation result of the CPU 401, thereby outputting data to the outside. Furthermore, the internal state can be changed by external communication commands. It has to be able to further.

  FIG. 4 shows a connection relationship between the control unit 120, the linear air-fuel ratio sensor 10, and the heater 30. A signal representing the oxygen concentration obtained from the detection element 20 of the linear air-fuel ratio sensor 10 is sent via the sensor signal processing circuit 26. Input to the control unit 120. The heater 30 is energized from the battery 37 according to ON (conducting) / OFF (non-conducting) of the transistor 36, generates heat according to the energization amount (time), and heats the detection element 20. In order to control the heating temperature, a control signal (duty signal) for turning ON / OFF the transistor 36 is supplied from the control unit 120. Note that the voltage value (or current value) at both ends of the transistor 36 is taken into the control unit 120 for use in failure diagnosis of the heater 30 and the like.

  Next, a control example for preventing the detection element 20 from causing defects such as cracks and breakage when the control unit 120 heats the detection element 20 with the heater 30 immediately after the engine is started will be described. .

  As described above, the moisture generated by the combustion is discharged as water vapor if the exhaust pipe temperature is above the dew point, but if the exhaust pipe temperature is below the dew point, it forms water droplets on the wall surface of the exhaust pipe 109 to cause condensation. In addition, moisture (condensation water) also adheres to the surface 20s of the detection element 20.

  In addition, the heating by the heater 30 does not have a uniform temperature distribution with respect to the detection element 20, the heater vicinity (inside) 20 i is high, and the surface portion 20 s away from the heater 30 is low. Thermal stress is generated. The temperature difference varies depending on the thermal resistance of the sensing element 20. When the thermal resistance is large, heat is accumulated inside and the temperature difference becomes large.

  Therefore, assuming that the temperature of the heater 30 (the heating amount for the detection element 20) is constant, as shown in FIG. 5, the temperature in the vicinity of the heater (inside) 20i is high immediately after energizing the heater 30 (immediately after starting the engine). Thus, the temperature difference from the surface portion 20s is maximized.

  If moisture adheres to the sensing element surface 20s, the element surface 20s has a latent heat of moisture. Therefore, even if heated, the element surface 20s is maintained at 100 ° C. while the moisture evaporates. Therefore, the temperature difference further increases. Although the temperature rise rate of the element surface 20s during the evaporation of water is substantially zero, it rapidly rises immediately after the water is used up.

  Therefore, in the present embodiment, when the control unit 120 estimates the moisture adhesion state of the surface 20s of the detection element 20 at the time of starting the engine, there is a possibility that moisture (condensation water) may adhere to the surface 20s. The temperature (heating amount) of the heater 30 immediately after starting is suppressed to a relatively low temperature without rapidly increasing as in the prior art, and the temperature between the interior 20i of the detection element 20 near the heater 30 and the surface 20s away from the heater 30 Warm-up control is performed to control the temperature of the heater 30 so that the difference does not exceed a predetermined value.

  Then, the warm-up control is continued until the time when all the moisture on the element surface 20s evaporates (this is also estimated based on the heat generation amount of the exhaust gas = the integrated value of the intake air amount, etc.). After the estimated time, sensor activation promotion control is performed to increase the temperature of the sensing element 20 to the activation temperature (about 600 ° C. or higher), and after the sensing element 20 reaches the activation temperature, the optimum temperature is achieved by feedback control. (For example, about 750 ° C. to 760 ° C.). The feedback control requires the actual temperature of the sensing element 20, but the actual temperature of the sensing element 20 is obtained based on a signal obtained from the sensing element 20 when it reaches 400 ° C to 500 ° C. Can do.

  Since the moisture adhesion state of the element surface 20s at the time of starting the engine differs depending on the temperature of the exhaust pipe 109 at the time of starting the engine, in this embodiment, the engine that can be regarded as substantially the same as the temperature of the exhaust pipe 109. The water adhering state of the sensing element surface 20s is estimated on the basis of the cooling water temperature and the intake air temperature (only one of them is acceptable).

  Further, the control unit 120 estimates a condensed water amount Mcon generated in the exhaust pipe 109 by the condensed water amount estimation control.

Hereinafter, a method for estimating the amount of condensed water Mcon generated in the exhaust pipe 109 will be described.
Based on the intake air amount Mair [g / s] per unit time and the fuel injection amount Mfue [g / s] per unit time, the water vapor amount Mwgs per unit time generated by the combustion reaction between the fuel and the intake air g / s] is calculated.

  Further, the exhaust gas temperature Tg (for example, the exhaust gas temperature in the vicinity of the exhaust port) is estimated based on the intake air amount, the engine speed, and the like. The exhaust gas temperature Tg may be detected by a temperature sensor. Further, the exhaust pipe temperature Tp (for example, the exhaust pipe temperature in the vicinity of the oxygen sensor 26) is estimated by a method described later.

  Then, a condensation ratio C corresponding to the current exhaust gas temperature Tg and the exhaust pipe temperature Tp is calculated with reference to a map of the condensation ratio C using the exhaust gas temperature Tg and the exhaust pipe temperature Tp as parameters. This condensation rate C is the rate of condensation in the exhaust pipe 25 of the water vapor (water vapor in the exhaust gas) generated by the combustion reaction between the fuel and the intake air. The map of the condensation ratio C is created in advance using the relationship between the exhaust gas temperature Tg, the exhaust pipe temperature Tp, and the condensation ratio C obtained based on experimental data, design data, etc., and is stored in the ROM of the control unit 120. ing.

  Thereafter, the water vapor amount Mwgs is multiplied by the condensation ratio C and the calculation cycle Δt to calculate the condensed water increase amount ΔMcon [g] per calculation cycle Δt.

ΔMcon = Mwgs × C × Δt
Thereafter, the current condensed water amount increase ΔMcon is added to the previous condensed water amount estimated value Mcon to obtain the current condensed water amount estimated value Mcon [g].

Mcon = Mcon + ΔMcon
This condensed water amount estimated value Mcon is stored in a backup RAM (storage means) of the control unit 120. The data stored in the backup RAM of the control unit 120 is retained even when the engine is stopped when an IG switch (ignition switch) (not shown) is turned off. When estimating the condensed water amount Mcon when the engine is restarted, the estimated condensed water amount Mcon stored immediately before the previous engine stop (that is, the estimated amount of condensed water remaining in the exhaust pipe 109 while the engine is stopped) is an initial value. And

  By the way, when the amount of intake air increases due to accelerator depression or the like and the amount of exhaust gas flowing through the exhaust pipe 109 increases, the condensed water accumulated in the exhaust pipe 109 is blown away by the exhaust gas and discharged outside the exhaust pipe 109. The

  Therefore, in this embodiment, when the intake air amount Mair exceeds the predetermined value Mth, the condensed water amount estimated value Mcon is reset to zero. Alternatively, the condensed water amount estimated value Mcon may be decreased according to the intake air amount Mair. Thus, when the intake air amount Mair increases and the amount of exhaust gas flowing through the exhaust pipe 109 increases, the condensed water accumulated in the exhaust pipe 109 is blown off by the exhaust gas and discharged outside the exhaust pipe 109. In response to this, the condensed water amount estimation value Mcon is reset to 0 or decreased.

Next, a method for estimating the exhaust pipe temperature Tp will be described.
The control unit 120 estimates the exhaust pipe temperature Tp by an estimation method during engine operation (see FIG. 6) during engine operation (period from engine start to IG switch OFF), and engine stop (IG switch ON). During the period from engine start to engine start), the exhaust pipe temperature Tp is estimated by an estimation method during engine stop (see FIG. 7).

  As shown in FIG. 6, when estimating the exhaust pipe temperature Tp during engine operation, first, the heat receiving side heat transfer coefficient Kin for obtaining the amount of heat received from the exhaust gas to the exhaust pipe 109, and the exhaust pipe A heat radiation side heat transfer coefficient Kout for calculating a heat radiation amount radiated from 109 to the outside air is calculated.

  When calculating the heat-receiving-side heat transfer coefficient Kin, the current engine is referred to by referring to a map of the correction coefficient α using the engine speed (substitution information of exhaust flow velocity) and the load (substitution information of exhaust pressure) as parameters. A correction coefficient α corresponding to the rotational speed and load is calculated.

  The correction coefficient α is a coefficient for correcting the heat receiving side heat transfer coefficient basic value Kin0. The map of the correction coefficient α is created in advance using the relationship between the engine rotational speed, the load, and the amount of heat received by the exhaust pipe 109 obtained based on experimental data, design data, and the like, and is stored in the ROM of the control unit 120. Yes. In general, the amount of heat received by the exhaust pipe 109 decreases as the engine speed increases and the exhaust flow rate increases, and the amount of heat received by the exhaust pipe 109 increases as the load increases and the exhaust pressure increases. Is set such that the higher the engine speed, the smaller the correction coefficient α and the smaller the heat receiving side heat transfer coefficient Kin, and the larger the load, the larger the correction coefficient α and the larger the heat receiving side heat transfer coefficient Kin. Yes.

  Thereafter, the heat receiving side heat transfer coefficient Kin is obtained by multiplying the heat receiving side heat transfer coefficient basic value Kin0 by the correction coefficient α.

Kin = Kin0 × α
As a result, the heat-receiving-side heat transfer coefficient Kin is changed by correcting the heat-receiving-side heat transfer coefficient basic value Kin0 in accordance with the engine speed (substitution information for the exhaust gas flow rate) and the load (substitution information for the exhaust pressure).

  Further, when calculating the heat radiation side heat transfer coefficient Kout, the correction coefficient β according to the current radiator fan rotation speed and the vehicle speed is referred to by referring to the map of the correction coefficient β using the radiator fan rotation speed and the vehicle speed as parameters. β is calculated.

  The correction coefficient β is a coefficient for correcting the heat radiation side heat transfer coefficient basic value Kout0. The map of the correction coefficient β is created in advance using the relationship between the radiator fan rotation speed, the vehicle speed, and the heat dissipation amount of the exhaust pipe 109, which is obtained based on experimental data, design data, and the like, and is stored in the ROM of the control unit 120. ing. In general, the higher the radiator fan rotational speed and the vehicle speed, the greater the heat radiation amount of the exhaust pipe 109. Therefore, the correction coefficient β map shows that the higher the radiator fan rotational speed and the vehicle speed, the larger the correction coefficient β and the heat dissipation side heat transfer coefficient. Kout is set to be large. As the atmospheric pressure (pressure outside the exhaust pipe 109) increases, the amount of heat released from the exhaust pipe 109 increases. Therefore, as the atmospheric pressure increases, the correction coefficient β increases to increase the heat radiation side heat transfer coefficient Kout. May be.

  Thereafter, the heat radiation side heat transfer coefficient Kout is obtained by multiplying the heat radiation side heat transfer coefficient basic value Kout0 by the correction coefficient β.

Kout = Kout0 × β
As a result, the heat dissipation side heat transfer coefficient Kout is changed by correcting the heat dissipation side heat transfer coefficient basic value Kout0 according to the rotational speed of the radiator fan and the vehicle speed.

  After calculating the heat receiving side heat transfer coefficient Kin and the heat radiating side heat transfer coefficient Kout in this way, the difference (Tg−Tp) between the exhaust gas temperature Tg and the exhaust pipe temperature Tp is multiplied by the heat receiving side heat transfer coefficient Kin. Then, the amount of heat received by the exhaust pipe 109 {Kin × (Tg−Tp)} is obtained, and the difference between the exhaust pipe temperature Tp and the outside air temperature Ta (Tp−Ta) is multiplied by the heat radiation side heat transfer coefficient Kout. The heat dissipation amount {Kout × (Tp−Ta)} of 109 is obtained.

  Then, using the heat reception amount {Kin × (Tg−Tp)} of the exhaust pipe 109, the heat release amount {Kout × (Tp−Ta)} of the exhaust pipe 109, the heat capacity Cp of the exhaust pipe 109, and the calculation period Δt, Is used to calculate the exhaust pipe temperature change amount ΔTp per calculation cycle Δt.

ΔTp = {Kin × (Tg−Tp) −Kout × (Tp−Ta)} / Cp × Δt
Thereafter, the current exhaust pipe temperature estimated value Tp is obtained by adding the current exhaust pipe temperature change amount ΔTp to the previous exhaust pipe temperature estimated value Tp.

Tp = Tp + ΔTp
This exhaust pipe temperature estimated value Tp is stored in the backup RAM of the control unit 120. When the exhaust pipe temperature Tp is estimated when the engine is restarted, the exhaust pipe temperature estimated value Tp estimated immediately before the engine is started by an estimation method during engine stop, which will be described later, is used as an initial value.

  On the other hand, as shown in FIG. 7, when the exhaust pipe temperature Tp is estimated while the engine is stopped (the period from when the IG switch is turned on to when the engine is started), first, the exhaust pipe temperature decrease rate D using the engine stop time as a parameter. Referring to the map, the exhaust pipe temperature decrease rate D corresponding to the current engine stop time is calculated. The map of the exhaust pipe temperature decrease rate D is created in advance using the relationship between the engine stop time and the exhaust pipe temperature decrease rate D obtained based on experimental data, design data, etc., and stored in the ROM of the control unit 120. Has been.

  Thereafter, the difference (Tpz-Ta) between the estimated exhaust pipe temperature Tpz immediately before the engine stop and the outside air temperature Ta (Tpz-Ta) is multiplied by the exhaust pipe temperature decrease rate D, and this value is added to the outside air temperature Ta to obtain the exhaust pipe. A temperature estimated value Tp is obtained.

Tp = (Tpz−Ta) × D + Ta
By the way, when the linear air-fuel ratio sensor 10 is heated by a heater and is in a high temperature state and condensed water adheres and gets wet, the sensor element may be broken.

  In consideration of these circumstances, in the present embodiment, the heater control of the linear air-fuel ratio sensor 10 is prohibited (or when the estimated condensate amount Mcon becomes equal to or greater than the predetermined value M1 and the possibility of being flooded increases (or Restrict. As a result, failure or abnormal operation of the linear air-fuel ratio sensor 10 due to flooding can be prevented in advance, and a state where the heater of the linear air-fuel ratio sensor 10 cannot normally operate due to flooding is regarded as an abnormality of the heater of the linear air-fuel ratio sensor 10. Preventing misdiagnosis in advance.

  Since the estimated value of the condensed water amount starts from 0 kg (dry state) immediately after the engine is started, the condensate amount (estimated value) calculated by the exhaust pipe model and the element crack even if the linear air-fuel ratio sensor 10 is submerged. In a method for comparing the limit water amount (hereinafter referred to as the water yield strength upper limit value) that does not generate water, immediately after the start (time point t0), the amount of condensed water (estimated value) becomes the water yield strength upper limit value (energization threshold value). Since it is unclear whether or not the maximum value of the condensed water amount exceeds the energization threshold value M1, it cannot be determined whether or not the heater of the linear air-fuel ratio sensor 10 should be turned on (energized).

Therefore, in the embodiment of the present invention, the following processing is performed.
That is, as described in FIG. 11 and FIG. 12, the worst condition in which the amount of condensed water is maximized from the starting water temperature and the starting intake air temperature (outside air temperature) (here, when idling is left where exhaust heat is minimized). The maximum value of the amount of condensed water (condensed water amount when idling) is given on a map (condensed water amount (A value) in condition A). On the other hand, the amount of condensed water (estimated value) calculated from the above-described exhaust pipe model is set as the amount of condensed water (B value) in Condition B.

  The amount of condensed water in the condition B calculated from the exhaust pipe model increases the exhaust heat when traveling is started, so that the condensed water evaporates faster and the amount of condensed water decreases more quickly than when idle.

  Therefore, after the start-up, the amount of condensed water in condition A is switched to the amount of condensed water in condition B calculated correctly. The switching timing is the moment when the amount of condensate in condition B starts to decrease from the increase (maximum value), that is, the time when the amount of condensate calculated this time becomes smaller than the amount of condensate calculated last time (switching at this time). A command is issued).

  Then, as the amount of condensed water used to determine the timing of starting energization of the heater, the condensation under worst conditions (when idling) is continued until the amount of condensed water (B value) calculated by the exhaust pipe model starts to decrease from the maximum value. The maximum value (A value) of the estimated water amount is used, and after that, the amount of condensed water (B value) calculated by the exhaust pipe model is used. When the upper limit value (determination threshold value M1) is exceeded, energization of the heater is prohibited or restricted until the amount of condensed water becomes equal to or less than the upper limit value of water resistance. When the amount of condensed water (A value) in condition A is equal to or less than the water yield strength upper limit (energization threshold M1) at the time of starting, it is considered that the amount of condensed water will not exceed the energization threshold M1 after that. Immediately after, for example, when the engine speed exceeds a predetermined value N1, energization of the heater is started.

  Here, as a heater energization method of the linear air-fuel ratio sensor 10 of the embodiment of the present invention, the amount of condensed water generated in the temperature range in advance from the cooling water temperature, the intake air temperature, and the outside air temperature at the time of engine start, for example, FIG. Then, by predicting with the map shown in FIG. 12 and comparing with the energization threshold value M1 of the condensed water amount estimated value Mcon, it is determined whether or not heater energization is possible.

  As shown in FIG. 8, when the energization threshold M1 is larger than the predicted amount of condensed water generation, it can be predicted that condensed water will not be generated to the extent that the sensor element will break in the corresponding water temperature range at the time of starting. Energize.

  As shown in FIG. 9, when the energization threshold M1 is smaller than the predicted amount of condensed water generation, there is a possibility that condensed water is generated to the extent that the sensor element is broken. When the condensed water begins to decrease due to evaporation after starting, if the condensed water amount estimated value Mcon is smaller than the predetermined value M1, it can be determined that the condensed water is not generated enough to break the sensor element. Start energizing the heater.

  On the other hand, as shown in FIG. 10, when the condensed water starts to decrease due to evaporation after starting, if the condensed water amount estimated value Mcon is larger than the predetermined value M1, the sensor element is broken, so the condensed water amount estimated value Mcon is predetermined. The heater is not energized until the value M1 or less.

  Thus, in the present invention, the amount of condensed water generated is predicted from the cooling water temperature, the intake air temperature, and the outside air temperature, and the energization timing to the heater is varied based on the predicted amount of condensed water generated. Since energization timing to the heater can be set at an appropriate timing based on the temperature region, element cracking of the linear air-fuel ratio sensor 10 can be prevented.

DESCRIPTION OF SYMBOLS 1 Control apparatus 10 Linear air fuel ratio sensor 20 Detection element 30 Heater 100 Internal combustion engine 101 Fuel injection valve 102 Spark plug 103 Ignition coil 104 Throttle valve 110 Water temperature sensor 111 Crank angle sensor 112 Cam angle sensor 113 Throttle position sensor 114 Intake pipe pressure sensor 115 Intake air flow meter 118 Catalyst 119 Oxygen sensor 120 Control unit 121 Intake air temperature sensor 122 Exhaust air temperature sensor

Claims (5)

In a control device for an internal combustion engine that controls an energization state of a heater that heats an exhaust gas sensor provided in an exhaust pipe of the internal combustion engine,
A water vapor amount calculating means for calculating a water vapor amount generated by combustion based on a fuel injection amount and an intake air amount of an internal combustion engine;
Exhaust gas temperature acquisition means for estimating or detecting the temperature of the exhaust gas of the internal combustion engine;
Exhaust pipe temperature acquisition means for estimating or detecting the temperature of the exhaust pipe of the internal combustion engine;
First condensate amount estimation means for estimating the amount of condensate generated in the exhaust pipe based on the water vapor amount, the exhaust gas temperature, and the exhaust pipe temperature;
A second condensate amount estimating means for predicting a maximum condensate amount in a temperature range preliminarily estimated from at least one of a cooling water temperature, an intake air temperature, and an outside air temperature when starting the internal combustion engine;
A control apparatus for an internal combustion engine, comprising: a heating control unit that controls to allow energization of the heater when the amount of condensed water or the maximum amount of condensed water is determined to be equal to or less than a predetermined value. The control apparatus for an internal combustion engine according to claim 1,
When the predetermined value is large by comparing the predetermined value and the maximum amount of condensed water when starting the internal combustion engine,
The control apparatus for an internal combustion engine, wherein the heating control means permits energization of the heater immediately after starting. The control apparatus for an internal combustion engine according to claim 1,
When the predetermined value is small by comparing the predetermined value and the maximum amount of condensed water when the internal combustion engine is started,
The control apparatus for an internal combustion engine, wherein the heating control means does not permit energization of the heater. The control apparatus for an internal combustion engine according to claim 3,
When the amount of condensed water after the internal combustion engine starts is smaller than the predetermined value when it starts to decrease due to evaporation,
The control device for an internal combustion engine, wherein the heating control means permits energization of the heater. The control apparatus for an internal combustion engine according to claim 3,
When the amount of condensed water after starting the internal combustion engine is greater than the predetermined value when starting to decrease due to evaporation,
The control device for an internal combustion engine, wherein the heating control means does not permit energization of the heater until the amount of condensed water becomes equal to or less than the predetermined value.