JP5798059B2 - Engine control device - Google Patents

Description

  The present invention relates to an engine control device in which an exhaust sensor (A / F sensor) provided with a heater for heating is arranged in an exhaust pipe (exhaust passage). In particular, the amount of condensed water accumulated in the exhaust pipe is newly increased. The present invention relates to a sensor that can be accurately estimated without requiring sensors and that can reliably prevent damage to an exhaust sensor due to condensed water without causing a significant increase in cost.

  In recent years, in order to reduce the environmental load, it has been required to purify exhaust gas discharged from the engine (engine). For that purpose, the air-fuel ratio of the air-fuel mixture used for combustion must be controlled within an appropriate range. Is required.

  Conventionally, in order to control the air-fuel ratio within an appropriate range, the oxygen concentration in the exhaust gas is detected, and the fuel supply amount is feedback-controlled so that the oxygen amount becomes substantially zero. In order to detect the oxygen concentration, an exhaust sensor such as an oxygen sensor that generates a voltage according to the oxygen concentration ratio or a linear air-fuel ratio sensor that can linearly detect the oxygen concentration is used.

  However, the temperature at which the oxygen sensor (the oxygen concentration detecting element) normally operates (activates) is 300 ° C. or higher, and the temperature at which the linear air-fuel ratio sensor (the oxygen concentration detecting element) operates normally (activates) is 600 ° C. As described above, it is necessary to forcibly heat the detection element of the sensor with a heating means such as a heater until the temperature exceeds the activation temperature.

  For this reason, conventionally, a heater for detecting element heating is attached to the sensor (a heater is usually arranged in the vicinity of the detecting element inside the sensor), and the detecting element is heated by the heater. Yes.

  However, in order to activate the detection element of the sensor as soon as possible after starting the engine, rapid heating of the detection element by the heater is necessary. However, if rapid heating is performed, thermal stress accompanying the temperature rise at that time May cause a defect called cracking, element cracking, etc. in the sensing element, making it impossible to detect the oxygen concentration properly. In the worst case, the sensing element may be damaged and not function at all. there were.

  Possible causes of cracks, element cracks, and the like in the detection element of the sensor are as follows.

  Normally, in an engine, fuel injected from a fuel injection valve is vaporized and mixed in the intake air, the mixture is burned in a combustion chamber, and the combustion waste gas (exhaust gas) is formed in an exhaust pipe or the like. While being discharged to the exhaust pipe, the exhaust pipe is warmed by the exhaust gas. Since the heat generation amount of the exhaust gas is proportional to the fuel injection amount, that is, the intake air amount, the integrated value of the intake air amount becomes the heat generation amount.

  Further, engine exhaust gas contains water vapor generated by a combustion reaction between fuel and intake air. When the exhaust gas containing water vapor is cooled in the exhaust pipe, the water vapor in the exhaust gas is condensed in the exhaust pipe to generate condensed water. More specifically, if the exhaust pipe (wall surface) temperature is equal to or higher than the dew point, water vapor is discharged. If the exhaust pipe temperature is equal to or lower than the dew point, water droplets are condensed on the exhaust pipe wall surface.

  In particular, if the exhaust pipe is curved and gas is likely to accumulate at the top, water vapor will accumulate at the top of the curved part, and when the exhaust pipe temperature decreases after the engine stops, the accumulated water vapor will Condensation. For this reason, when the sensor is attached to the curved portion, moisture tends to adhere to the surface of the detection element. Moisture adhering to the surface of the detection element is a main cause of the occurrence of defects such as element cracking. Before explaining this, an example of an exhaust sensor equipped with a heater for heating that is currently in practical use ( A linear air-fuel ratio sensor (also used in an embodiment of the present invention described later) will be described with reference to FIGS. 3 (A) and 3 (B).

  A linear air-fuel ratio sensor 10 shown in FIG. 3A has a cylindrical holder 11 attached to an exhaust pipe 109 and a protector 12 inserted into the exhaust pipe 109, and an oxygen concentration detection element in the protector 12. 20 is arranged. The protector 12 is formed with several holes 14 through which exhaust gas enters and exits.

  As shown in FIG. 3 (B), the detection element 20 has a multilayer structure including upper and lower protective layers 23 and 24, and a heater portion 29 containing a heating wire heater 30 is disposed on the lower surface side thereof. Has been.

  The detection element 20 includes a detection electrode 21 and a reference electrode 22, and a predetermined current flows through the diffusion layer 25 sandwiched between the detection electrode 21 and the reference electrode 22, and oxygen in exhaust gas flowing through the exhaust pipe 109. In accordance with the concentration, oxygen is moved so that the oxygen concentration ratio between the detection electrode 21 side and the reference electrode 22 side is constant. Since the current value at this time is proportional to the oxygen concentration on the exhaust pipe 109 side, the oxygen concentration in the exhaust pipe (exhaust gas) can be detected by measuring the current value. The oxygen concentration is oxygen that has not reacted during combustion and corresponds to the air-fuel ratio. Therefore, it has a current characteristic as shown in FIG. 4 according to the air-fuel ratio.

  In order for the sensing element 20 to function normally, it is necessary to heat to a temperature (600 ° C. or higher) at which oxygen can move as ions. If the exhaust gas is 600 ° C. or higher, heating with the exhaust gas is possible, but in normal operation, the exhaust gas temperature is 600 ° C. or lower, and heating with the heater 30 is necessary.

  On the other hand, 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, if the temperature of the heater 30 is constant, as shown in FIG. 6, the temperature of the heater vicinity (inside) 20i increases immediately after energization of the heater 30 (immediately after engine start), and the temperature with the surface portion 20s. The difference 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 sensing element surface 20s during the evaporation of moisture is substantially zero, it rises rapidly immediately after the water has disappeared, so the temperature rise rate becomes extremely large. Such a temperature difference between the inside 20i of the sensing element 20 and the surface 20s and a thermal stress accompanying a rapid temperature rise are considered to cause defects such as cracks and element cracks in the sensing element 20.

  As a countermeasure against the occurrence of problems such as element cracks in such an exhaust sensor (detection element thereof), a temperature sensor has conventionally been arranged outside the exhaust pipe as described in Patent Document 1, for example. The temperature sensor estimates the temperature in the exhaust pipe, determines whether or not the condensed water can exist in the exhaust pipe based on the temperature, and if the condensed water can exist, burns the exhaust pipe It has been proposed to heat with a heat medium heated by a burner.

JP 2004-316594 A

  However, in the countermeasures as in the prior art, it is necessary to newly provide an exhaust pipe heating means for heating an upstream portion of the temperature sensor or the exhaust pipe from the exhaust sensor, which increases the manufacturing cost accordingly. was there.

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to accurately estimate the amount of condensed water accumulated in the exhaust pipe without the need to newly provide sensors or heating means. Thus, it is an object of the present invention to provide an engine control device that can reliably prevent element cracking or the like of an exhaust sensor due to condensed water without causing a significant increase in cost.

In order to achieve the above object, an engine control device according to the present invention is configured to perform energization control on a heater for detecting element heating of an exhaust sensor on the basis of the amount of condensed water in an exhaust pipe, and a fuel injection amount and an intake air amount. A water vapor amount calculating means for calculating the amount of water vapor generated by combustion based on the above, an exhaust gas temperature acquiring means for estimating or detecting the temperature of the exhaust gas, and an exhaust pipe temperature acquiring means for estimating or detecting the temperature of the exhaust pipe And a 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 . In the energization control for the heater, the condensate amount estimation value estimated by the condensate amount estimation unit is compared with a preset water yield strength upper limit value, and the energization control for the heater is controlled based on the comparison result. When the engine is started and the estimated amount of condensed water exceeds the water yield strength upper limit value, until the condensed water amount estimated value becomes equal to or less than the water yield strength upper limit value, It is characterized by prohibiting or restricting energization to the heater .

According to the present invention, parameters normally detected or estimated by sensors provided in the engine, specifically, the water vapor amount, exhaust gas temperature, and exhaust pipe temperature obtained from the fuel injection amount and the intake air amount. The amount of condensed water is estimated based on the amount of water, and the energization control is performed on the heater for detecting element of the exhaust sensor based on the amount of condensed water, so that there is no need to newly provide sensors or heating means. In addition to being able to accurately grasp the amount of condensed water accumulated in the exhaust pipe, it is possible to properly control the energization of the heater for heating the exhaust sensor. It can be surely prevented without incurring an increase.
Problems, configurations, and effects other than those described above will be clarified by the following embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows one Embodiment of the control apparatus of the engine which concerns on this invention with an example of the vehicle-mounted engine to which it is applied. The figure which is provided for description of the surroundings of the control unit which comprises the principal part of the control apparatus shown by FIG. FIG. 1 is a linear air-fuel ratio sensor used in the engine shown in FIG. 1, wherein (A) is an overall side view showing a mounted state of the linear air-fuel ratio sensor, and (B) is a partially cutaway perspective view showing a structure of a detection element. . The figure which shows the output characteristic of the linear air fuel ratio sensor of FIG. The figure which shows the connection relation of the control unit shown in FIG. 1, a linear air fuel ratio sensor, and a heater. The figure which shows the temperature rise characteristic of the detection element immediately after starting of the linear air fuel ratio sensor of FIG. The block diagram which shows an example of the process (The exhaust pipe temperature variation | change_quantity (DELTA) Tp calculation per calculation period (DELTA) t in engine operation) performed when the control unit shown by FIG. 1 estimates the amount of condensed water. The block diagram which shows an example of the process (exhaust pipe temperature estimation at the time of an engine stop) performed when the control unit shown by FIG. 1 estimates the amount of condensed water. The time chart which shows transition of the exhaust pipe temperature Tp during engine operation-> stop period. FIG. 2 is a block diagram showing an example of processing executed when the control unit shown in FIG. 1 estimates the amount of condensed water (condensed water amount estimation and energization control to the linear air-fuel ratio sensor). The figure used for description of the problem for onboard mounting of the exhaust pipe model (condensed water amount estimation model) on the ECU and the measures for solving it. The figure which is provided for description of the setting of the timing which turns ON the heater of a linear air fuel ratio sensor in this invention Example. FIG. 4 is a block circuit diagram for explaining the setting of timing for turning on (energizing) the heater of the linear air-fuel ratio sensor in the embodiment of the present invention. 4 is a time chart for explaining the setting of timing for turning on (energizing) the heater of the linear air-fuel ratio sensor in the embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an in-vehicle engine having an exhaust sensor with a heater to which a control device according to the present invention is applied.

  The illustrated engine 100 is, for example, an in-line four-cylinder gasoline engine, and a spark plug 102 to which an ignition voltage is applied from an ignition coil 103 is disposed on the head (combustion chamber) of a cylinder 107 in which a water temperature sensor 110 is disposed. Further, a crank angle sensor 111 and a cam angle sensor 112 are provided in relation to the crankshaft and the intake / exhaust valve operating mechanism, and a fuel injection valve 101, an electric throttle valve 104, A throttle (opening) sensor 113, an intake pipe pressure sensor 114, an air flow sensor 115, an intake air temperature sensor 121 for detecting an intake air temperature (which can be regarded as an outside air temperature), and the like are disposed. As shown in FIG. 3, a linear air-fuel ratio sensor 10, an exhaust temperature sensor 122 for detecting the exhaust gas temperature, a catalyst 118, and the like are arranged.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.

  In the control device of the present embodiment, energization (ON / OFF and temperature (heat generation amount)) control of the detection element heating heater 30 (see FIG. 3) provided in the linear air-fuel ratio sensor 10 is performed. A control unit 120 is provided to control the fuel injection amount and fuel injection timing by the fuel injection valve 101 and the ignition timing by the spark plug 102.

  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 representing the operating state, 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 for controlling an actuator (fuel pump 117, electric throttle valve 104, etc.) based on the calculation result of the CPU 401 are provided. Is output to the outside, and from the outside And to be able to change the internal state by Shin command.

  FIG. 5 shows the connection relationship between the control unit 120, the linear air-fuel ratio sensor 10, and the heater 30, and a signal (see FIG. 4) representing the oxygen concentration obtained from the detection element 20 of the linear air-fuel ratio sensor 10 is sensor signal processing. The signal is input to the control unit 120 via the circuit 26. 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 description will be given of a control example for preventing the detection element 20 from causing defects such as cracks and element cracks when the control unit 120 heats the detection element 20 with the heater 30 immediately after starting the engine. To do.

  As described above, moisture generated by combustion is discharged as water vapor when the exhaust pipe (wall surface) temperature is equal to or higher than the dew point. However, when the exhaust pipe temperature is equal to or lower than the dew point, water drops on the inner wall surface of the exhaust pipe 109 are discharged. As a result, condensation occurs, and moisture (condensation water) also adheres to the surface 20 s 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. 6, the temperature in the vicinity of the heater (inside) 20i is high immediately after energization of the heater 30 (immediately after engine start). 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 (condensed 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 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. Based on the cooling water temperature and the intake air temperature (only one of them is acceptable), the moisture adhesion state of the sensing element surface 20s is estimated.

  In addition, the control unit 120 is configured as shown in FIG. 7 (exhaust pipe temperature change amount ΔTp calculation per calculation period Δt during engine operation), FIG. 8 (exhaust pipe temperature estimation when the engine is stopped), FIG. The amount of condensate water Mcon generated in the exhaust pipe 109 is estimated by executing a process (program) as shown in FIG.

Hereinafter, a method for estimating the amount of condensed water Mcon generated in the exhaust pipe 109 will be described.
First, as shown in the equation shown in the following [Equation 1], the sum of the intake air amount Mail [g / s] per unit time and the fuel injection amount Mfue [g / s] per unit time is calculated as follows. Since the water vapor amount Mwgs [g / s] per unit time generated by the combustion reaction of the intake air is equal to the sum of the carbon dioxide amount Mco2 [g / s] per unit time, the water vapor amount Mwgs [ 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. This function serves as “exhaust gas temperature acquisition means”. 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 linear air-fuel ratio sensor 10) 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 109 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 by the following equation.
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] by the following equation.
Mcon = Mcon + ΔMcon

  This condensed water amount estimated value Mcon is stored in a backup RAM (storage means) of the control unit 120. Data stored in the backup RAM of the control unit 120 is held 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 value of the condensed water remaining in the exhaust pipe 109 while the engine is stopped) is an initial value. (Previous DC).

  By the way, when the amount of intake air increases due to depression of the accelerator pedal 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 off by the exhaust gas and discharged out of the exhaust pipe 109. Is done.

  Therefore, in this embodiment, when the intake air amount Mail 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 in accordance with the intake air amount Mail. As a result, 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. Correspondingly, 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.
As shown in FIG. 9 (time chart showing the transition of the exhaust pipe temperature Tp during the engine operation to the stop period), the control unit 120 operates while the engine is operating (the period from engine start to IG switch OFF). The exhaust pipe temperature Tp is estimated by an estimation method during operation (see FIG. 7). When the engine is stopped (the period from when the IG switch is turned off until the engine is started), the exhaust pipe is estimated by the estimation method during engine stop (see FIG. 8). The temperature Tp is estimated.

  In estimating the exhaust pipe temperature Tp during engine operation, as shown in FIG. 7, 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 rotation 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 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 Kin0 is multiplied by the correction coefficient α to obtain the heat-receiving-side heat transfer coefficient Kin by the following equation.
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 according to 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, a correction coefficient according to the current radiator fan rotation speed and the vehicle speed is referred to by referring to a 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 and the heat-radiation-side heat transfer coefficient Kout increases. May be.

Thereafter, the heat radiation side heat transfer coefficient Kout is obtained by the following equation 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 manner, 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 to obtain the exhaust pipe. 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 cycle Δt, To calculate the exhaust pipe temperature change amount ΔTp per calculation period 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

  The 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 (see FIG. 8) described later is used as an initial value.

  On the other hand, when estimating the exhaust pipe temperature Tp while the engine is stopped (the period from when the IG switch is turned off until starting), as shown in FIG. 8, first, the exhaust pipe temperature decrease rate D with the engine stop time as a parameter is used. 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 exhaust pipe temperature estimated value Tpz and the outside air temperature Ta immediately before the previous engine stop is multiplied by the exhaust pipe temperature decrease rate D, and the 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, as described above, when the linear air-fuel ratio sensor 10 is heated by a heater and condensed water adheres when it is in a high temperature state, the sensor element may be damaged (element crack).

  In consideration of these circumstances, in this embodiment, when the condensed water amount estimated value Mcon exceeds the predetermined determination threshold value (waterproof strength upper limit value described later) M1, the possibility of receiving water increases. The heater control (energization) of the linear air-fuel ratio sensor 10 is prohibited (or restricted), and the failure diagnosis of the heater of the linear air-fuel ratio sensor 10 is prohibited. 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.

  A problem for mounting the exhaust pipe model (condensed water amount estimation model) as described above on the ECU on board and measures for solving the problem will be described below.

  Since the amount of condensed water (estimated value) calculated by the exhaust pipe model starts from 0 kg (dry state) immediately after starting, the amount of condensed water (estimated value) calculated by the exhaust pipe model and the linear air-fuel ratio sensor 10 are submerged. However, in the method of comparing with the limit water amount (hereinafter referred to as the water yield strength upper limit value) at which no element crack occurs, as shown in FIGS. 11A and 11B, immediately after the start (time point t0). Is then unknown whether the amount of condensate (estimated value) exceeds the water yield strength upper limit (determination threshold M1), in other words, whether the maximum value of the condensate exceeds the determination threshold M1. Therefore, it cannot be determined whether or not the heater of the linear air-fuel ratio sensor 10 should be turned on (energized). Specifically, as shown in FIG. 11A, after the start (t0), the amount of condensed water (estimated value) increases and exceeds the water yield strength upper limit value (determination threshold M1) at time t1, When the maximum value is reached at t2 and then decreases and becomes equal to or less than the determination threshold value M1 at time t3, the heater may be turned on at time t3. However, as shown in FIG. If the amount of condensed water (estimated value) reaches the maximum value at time t2 ′ after starting, but starts to decrease without exceeding the water proof strength upper limit value (determination threshold value M1), the heater is turned on. The timing cannot be grasped (the amount of condensed water may exceed the upper limit of water resistance as shown in FIG. 11A after time t0, so it is not known when the heater is turned on after time t0). As a result, heater control can be performed properly. There is no fear.

In order to solve this problem, the following processing is performed in the embodiment of the present invention.
That is, as can be understood by referring to FIGS. 12, 13, and 14, the worst condition (here, the exhaust heat is the minimum) where the amount of condensed water is maximized from the starting water temperature and the starting intake air temperature (outside air temperature). The maximum value of the amount of condensed water (when the idle is left) (the amount of condensed water when the idle is left) is given on a map (the amount of condensed water (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 (shown in FIG. 13). A switching command is issued at this point as shown).

  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 lower than the upper limit value of water resistance. When the amount of condensed water (A value) in condition A is equal to or lower than the water yield strength upper limit (judgment threshold value M1) at the time of starting, it is considered that the condensed water amount will not exceed the judgment threshold value M1 thereafter. Therefore, energization of the heater is started immediately after starting, for example, when the engine speed exceeds a predetermined value N1.

  More specifically, the amount of condensed water used for determining the timing for turning on (energizing) the heater of the linear air-fuel ratio sensor 10 is as shown in FIG. 14 (A) [normal start] and FIG. In the case of FIG. 14C] [in the case of low temperature start], it becomes as shown by a thick solid line.

  Here, in the case of the normal start in FIG. 14A, the condensate water amount (A value) of the condition A at the start time (also the condensate water amount (B value) of the condition B) is the upper limit of the water resistance strength (determination threshold). M1) or less, it is considered that the amount of condensed water will not exceed the determination threshold value M1 thereafter. Therefore, immediately after starting, for example, at the time t11 when the engine speed exceeds the predetermined value N1, the heater is energized. To be started.

  On the other hand, in the case of the start-up immediate running of FIG. 14B, when the amount of condensed water (A value) in the condition A is switched to the amount of condensed water (B value) in the condition B, the amount of condensed water is equal to or less than the determination threshold value M1. Therefore, energization of the heater is started at time t12 immediately after switching from the A value to the B value.

  In the case of the low temperature start in FIG. 14C, the B value exceeds the determination threshold value M1 even after the amount of condensed water (A value) in the condition A is switched to the amount of condensed water (B value) in the condition B. Therefore, after switching from the A value to the B value, energization of the heater is started at time t13 when the B value becomes equal to or less than the determination threshold value M1.

  As described above, the amount of condensed water used for determining the start timing of energization of the heater is the worst condition (when idling) until the amount of condensed water (B value) calculated by the exhaust pipe model starts to decrease from the maximum value. The condensate water amount (B value) calculated by the exhaust pipe model is used thereafter, and the condensate water amount is reduced when the engine is started. If the water yield strength upper limit value (determination threshold M1) is exceeded, the energization of the heater is prohibited or restricted until the amount of condensed water becomes equal to or less than the water yield strength upper limit value. Immediately after start-up, only the amount of condensed water calculated from the exhaust pipe model, in other words, the heater energization control of the linear air-fuel ratio sensor 10 is not performed at the wrong heater energization timing. By the element crack or the like of the linear air-fuel ratio sensor 10, it can be reliably prevented without causing a significant cost increase.

  DESCRIPTION OF SYMBOLS 1 ... Control apparatus 10 ... Linear air-fuel ratio sensor 20 ... Detection element 30 ... Heater 100 ... 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 sensor 114 ... Intake pipe pressure sensor 115 ... Air flow sensor 118 ... Catalyst 119 ... Oxygen sensor 120 ... Control unit 121 ... Intake air temperature sensor, 122 ... Exhaust air temperature sensor

Claims (7)

An engine control device configured to perform energization control on a detection element heating heater of an exhaust sensor based on an amount of condensed water in an exhaust pipe,
A water vapor amount calculating means for calculating the amount of water vapor generated by combustion based on the fuel injection amount and the intake air amount;
Exhaust gas temperature acquisition means for estimating or detecting the temperature of the exhaust gas;
Exhaust pipe temperature acquisition means for estimating or detecting the temperature of the exhaust pipe;
A condensed water amount estimating means for estimating the amount of condensed water generated in the exhaust pipe based on the water vapor amount, the exhaust gas temperature, and the exhaust pipe temperature ;
In the energization control for the heater, the condensate amount estimation value estimated by the condensate amount estimation means is compared with a preset water yield strength upper limit value, and the energization control for the heater is controlled based on the comparison result. And
When the estimated amount of condensed water exceeds the water proof strength upper limit when the engine is started, the heater is energized until the condensed water amount estimated value becomes less than the water proof strength upper limit. An engine control device which is prohibited or restricted . An engine control device configured to perform energization control on a detection element heating heater of an exhaust sensor based on an amount of condensed water in an exhaust pipe,
Exhaust gas temperature acquisition means for estimating or detecting the temperature of the exhaust gas;
An intake air amount detection means for detecting an intake air amount;
An outside air temperature detecting means for detecting the outside air temperature;
When the engine is started, the exhaust gas temperature obtained by the exhaust gas temperature acquisition means, the intake air amount detected by the intake air amount detection means, and the outside air temperature detected by the outside air temperature detection means are used in the exhaust pipe. A condensate amount estimating means for estimating the amount of condensate accumulated ,
In the energization control for the heater, the condensate amount estimation value estimated by the condensate amount estimation means is compared with a preset water yield strength upper limit value, and the energization control for the heater is controlled based on the comparison result. And
When the estimated amount of condensed water exceeds the water proof strength upper limit when the engine is started, the heater is energized until the condensed water amount estimated value becomes less than the water proof strength upper limit. An engine control device which is prohibited or restricted . The amount of condensed water estimation means, the exhaust gas temperature, the intake air amount, and thereby estimates the wall temperature of the exhaust pipe with the outer air temperature, the air-fuel mixture obtained from said fuel injection amount and the intake air amount based on the air-fuel ratio estimating the dew point temperature of the exhaust pipe, determine the relative wall temperature from the estimated and the wall temperature and the dew point temperature, accumulated from said relative wall temperature and the intake air quantity to the exhaust pipe condensation of The engine control device according to claim 2, wherein the amount of water is estimated. Claim 1 timing of the energization control for the heater, and a startup coolant temperature start-up intake air temperature, amount of condensed water is characterized that you determined using the maximum value of the amount of water condensation estimated value under the worst conditions of maximum 4. The engine control device according to any one of 1 to 3 . As the maximum value of the amount of water condensation estimated value in the worst condition, according to claim 4 exhaust heat characterized that you determined by the timing with the maximum value of the amount of water condensation estimate at minimum idling state Engine control device. As the condensed water amount estimated value to be compared with the water yield strength upper limit value, until the condensed water amount estimated value estimated by the condensed water amount estimating means starts to decrease from the maximum value, the maximum value of the condensed water amount estimated value under the worst condition is reached. the used, thereafter the control device for an engine according to claim 4 or 5, characterized that you determined by the timing with the condensed water amount estimation value estimated by the amount of water condensation estimating means. The said condensed water amount estimation means reduces the said condensed water amount estimated value according to the intake air amount of an engine or the information correlated with it, or resets it to 0, The one of Claim 1 to 6 characterized by the above-mentioned. Engine control device.

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