JP2004353495A - Sensor protective device for detecting internal combustion engine exhaust gas component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent water from spattering on an air-fuel ratio sensor used in an internal combustion engine, and also prevent uncomfortable feeling of a driver. <P>SOLUTION: When it is determined that the air-fuel ratio sensor may be spattered by water (Texp≤Tdp) (YES in S108), the increments of a throttle opening is limited by a throttle opening updating amount guard value Δθ. Accordingly, an exhaust gas velocity is not rapidly increased, and an allowance for evaporation can be provided before water in an exhaust gas passage is spattered. Since the increments of an intake air amount are not limited, the driver can accelerate by continuing an acceleration operation. Since an exhaust gas tube wall temperature Texp is steadily increased by an increase in the intake air amount, the evaporation of the water content in the exhaust gas passage is also terminated rather earlier. As a result, a large uncomfortable feeling is not given to the driver. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sensor protection device provided in an exhaust pipe of an internal combustion engine to detect an exhaust component and activated by being heated by a heater at a low temperature.
[0002]
[Prior art]
In the internal combustion engine, feedback control is performed so that the exhaust air-fuel ratio becomes a target air-fuel ratio, for example, a stoichiometric air-fuel ratio, in order to purify the harmful components (HC, CO, NOx, etc.) in the exhaust gas with a catalyst. As an air-fuel ratio sensor for detecting the exhaust air-fuel ratio used in the air-fuel ratio feedback control, an O2 sensor for detecting whether the exhaust air-fuel ratio is rich or lean based on the oxygen concentration contained in the exhaust gas, and detecting an air-fuel ratio over a wide range. An air-fuel ratio sensor is used.
[0003]
In these sensors, it is indispensable that the sensors are maintained in an active state in order to maintain the detection accuracy. Usually, the heaters provided in the sensors are energized at the time of starting the internal combustion engine to heat them and activate them early. In order to maintain these active states, energization control of the heater is performed (for example, see Patent Document 1).
[0004]
When moisture attached to the inner wall surface of the exhaust pipe is splashed on the sensor heated by the heater and the sensor gets wet, the sensor is rapidly cooled, causing a thermal shock, which may cause a sensor crack. There is.
[0005]
In order to prevent such cracking of the sensor, in the above-described conventional example, when it is determined that moisture has adhered to the wall surface of the exhaust pipe, a process for suppressing the exhaust gas flow rate is executed, and the moisture content due to the high speed of the exhaust gas is increased. To prevent the sensor from getting wet.
[0006]
[Patent Document 1]
JP-A-2001-41923 (pages 7-8, FIG. 10)
[0007]
[Problems to be solved by the invention]
However, in order to suppress the exhaust flow velocity, the throttle valve opening degree reaches the guard value when the driver operates the accelerator because the throttle valve opening degree is set to a guard value in order to slow down the exhaust flow velocity. The throttle valve opening is fixed.
[0008]
Until the exhaust pipe temperature rises so that there is no risk of moisture adhering to the exhaust pipe inner wall, despite the driver continuing to perform the acceleration operation, the driver does not accelerate sufficiently and maintains the low vehicle speed state May be. Therefore, there is a possibility that the driver will feel great discomfort. In addition, since the rise of the exhaust pipe temperature is considerably delayed, the sense of incongruity tends to be remarkable.
[0009]
An object of the present invention is to prevent the sensor from being wet by water and also to suppress a feeling of strangeness to a driver.
[0010]
[Means for Solving the Problems]
Hereinafter, the means for achieving the above object and the effects thereof will be described.
The sensor protection device for detecting an exhaust component of an internal combustion engine according to claim 1 is a protection device for a sensor that is provided in an exhaust pipe of an internal combustion engine to detect an exhaust component and is activated by being heated by a heater. The wetness determination means for determining the possibility of being wetted by the sensor, and when the wetness determination means determines that there is a possibility of being wetted, the increase rate of the intake air amount of the internal combustion engine is determined. And means for restricting the amount of intake air to be restricted.
[0011]
The intake air amount limiting means limits the rate of increase of the intake air amount of the internal combustion engine when it is determined by the water determination means that there is a possibility of being wet.
Since the rate of increase in the amount of intake air is limited in this manner, the exhaust speed does not increase rapidly, and it is possible to allow the water on the inner wall of the exhaust pipe to evaporate before being scattered.
[0012]
In this case, since the increase rate of the intake air amount is limited, it is possible to increase the intake air amount itself, and if the driver continues the acceleration operation, the low intake air amount state is not maintained. There is no situation where acceleration is not possible. In addition, since the exhaust pipe temperature steadily rises due to the increase in the intake air amount, the evaporation of the water on the inner wall of the exhaust pipe ends relatively early. Therefore, it does not give the driver any great discomfort.
[0013]
Therefore, it is possible to prevent the sensor from being wet, and to suppress the driver from feeling uncomfortable.
According to a second aspect of the present invention, in the first aspect, the sensor is a sensor that detects an oxygen concentration in the exhaust gas.
[0014]
A sensor that is activated by being heated by the heater includes a sensor that detects the oxygen concentration in the exhaust gas. In such a sensor, it is possible to prevent a failure such as generation of a crack due to being wet, and to suppress a sense of discomfort to the driver.
[0015]
According to a third aspect of the present invention, in the sensor protection device for detecting an exhaust component of an internal combustion engine according to the first or second aspect, the water determination unit determines a possibility of the sensor being wet based on the exhaust gas temperature. And
[0016]
When the exhaust gas temperature is low, the dew point is easily reached, and moisture easily adheres to the inner wall of the exhaust pipe due to dew condensation. Therefore, it is possible to determine the possibility of the sensor being wetted based on the exhaust gas temperature.
[0017]
Therefore, when the wetness determining means determines that moisture easily adheres to the inner wall of the exhaust pipe, the intake air amount limiting means limits the rate of increase of the intake air amount of the internal combustion engine, thereby preventing the sensor from being wet. In addition, discomfort to the driver can be suppressed.
[0018]
According to a fourth aspect of the present invention, there is provided a sensor protection device for detecting an exhaust component of an internal combustion engine according to any one of the first to third aspects, wherein the intake air amount restricting unit sets an increasing rate of an adjustment amount by the intake air amount adjusting unit of the internal combustion engine. The limiting is to limit the rate of increase of the intake air amount.
[0019]
More specifically, the intake air amount limiting means can limit the increase rate of the intake air amount by limiting the increase rate of the adjustment amount by the intake air amount adjustment means of the internal combustion engine.・ Effects can be produced.
[0020]
According to a fifth aspect of the present invention, the intake air amount adjusting means is a throttle valve.
As the intake air amount adjusting means, a throttle valve can be mentioned. In particular, by using an electronically controlled throttle valve, the intake air amount limiting means can easily limit the increase rate of the intake air amount, Can be prevented from being wet, and a feeling of strangeness to the driver can be suppressed.
[0021]
According to a sixth aspect of the present invention, in the fourth aspect, the intake air amount adjusting means is an intake valve lift amount adjusting means.
[0022]
As the intake air amount adjusting means, a lift amount adjusting means for the intake valve can be mentioned. In this way, even by adjusting the lift amount of the intake valve, the intake air amount limiting means can easily limit the increase rate of the intake air amount, prevent the sensor from being wet, and suppress the driver's discomfort. Can be.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
[Embodiment 1]
FIG. 1 is a schematic configuration diagram of a gasoline engine (hereinafter, abbreviated as “engine”) 2 as an internal combustion engine mounted on a vehicle and an electronic control unit (hereinafter, referred to as “ECU”) 4 as a control device. ing. Although the engine 2 is a four-cylinder engine, FIG. 1 shows only one cylinder in a longitudinal sectional view. Each cylinder is a four-valve engine having two intake valves 2a and two exhaust valves 2b. The number of cylinders may be six or eight, and may be a two-valve engine or a five-valve engine.
[0024]
The output of the engine 2 is finally transmitted to the wheels via a transmission as running drive power. The engine 2 is provided with an ignition plug 14 for igniting an air-fuel mixture in the combustion chamber 10. The intake port 16 connected to the combustion chamber 10 is opened and closed by driving the intake valve 2a. A fuel injection valve 12 for injecting fuel toward the intake port 16 is provided for each cylinder in the middle of each intake passage 20 connected to the intake port 16. The intake passage 20 is connected to a surge tank 22, and a throttle valve 26 whose opening is adjusted by a motor 24 is provided upstream of the surge tank 22. The intake air amount GA is adjusted by the opening of the throttle valve 26 (throttle opening TA). The throttle opening TA is detected by the throttle opening sensor 28 and read into the ECU 4. The intake air amount GA is detected by an intake air amount sensor 30 provided upstream of the throttle valve 26, and the intake air temperature THA is detected by an intake air temperature sensor 31 provided upstream of the throttle valve 26 and read into the ECU 4. ing.
[0025]
The exhaust port 32 connected to the combustion chamber 10 is opened and closed by driving the exhaust valve 2b. Two three-way catalytic converters 38 and 40 are arranged in the exhaust passage 36 connected to the exhaust port 32. Among them, the upstream first three-way catalytic converter 38 is an electrically heated catalyst which can be activated early by heating of the electric heater, and the downstream second three-way catalytic converter 40 is mainly activated by the exhaust gas temperature. It is a catalyst. An exhaust passage 36 upstream of the first three-way catalytic converter 38 is provided with an air-fuel ratio sensor 42 for detecting an air-fuel ratio AF from the oxygen concentration in the exhaust gas. Is provided with an exhaust gas temperature sensor 44.
[0026]
Note that a heater for heating is provided in the air-fuel ratio sensor 42, and the air-fuel ratio sensor 42 is heated to an activation temperature by power supply control by the ECU 4.
The ECU 4 is an engine control circuit mainly composed of a digital computer. The ECU 4 inputs signals from sensors other than the above-described throttle opening sensor 28, intake air amount sensor 30, intake air temperature sensor 31, air-fuel ratio sensor 42, and exhaust gas temperature sensor 44 that detect the operating state of the engine 2. ing. That is, an accelerator opening sensor 48 for detecting the depression amount (accelerator opening ACCP) of the accelerator pedal 46, an engine speed sensor 50 for detecting the engine speed NE from the rotation of the crankshaft, and a reference crank from the rotation phase of the intake camshaft. A signal is input from a reference crank angle sensor 52 for determining an angle. Further, signals are input from a cooling water temperature sensor 54 for detecting the engine cooling water temperature THW and a vehicle inclination angle sensor 56 for detecting the inclination angle Vs of the vehicle. In addition, various sensors other than such a sensor are provided as needed.
[0027]
The ECU 4 controls the throttle opening degree TA, the fuel injection timing, the fuel injection amount, and the ignition of the engine 2 based on the control signals for the throttle valve motor 24, the fuel injection valve 12, and the ignition plug 14 based on the detection contents from the above-described sensors. Timing is appropriately controlled.
[0028]
Next, among the controls executed by the ECU 4, the throttle opening speed limiting control will be described. FIG. 2 shows a flowchart of this process. This process is a process repeatedly executed in a time cycle. Note that steps in the flowchart corresponding to individual processing contents are represented by “SＳ”.
[0029]
When the process is started, first, it is determined whether or not the standby time T0 has elapsed since the start of the engine 2 (S100). At the time of starting, it is necessary to control the engine output torque with a high response until the engine 2 reaches a stable rotation. Therefore, it is necessary to drive the throttle valve 26 quickly. For this reason, the time from the start to the stable rotation is measured in advance and stored as the standby time T0 in the ROM of the ECU 4. In step S100, the determination of the elapse of the standby time T0 from the start of the engine 2 determines the stabilization of the engine rotation.
[0030]
If the standby time T0 has not elapsed ("NO" in S100), the present process is temporarily terminated.
When the standby time T0 has elapsed (“YES” in S100), the intake air temperature THA (° C.) detected by the intake air temperature sensor 31 is read into the work area in the RAM of the ECU 4 (S102). Further, the intake air amount GA (g / s) detected by the intake air amount sensor 30 is similarly read into the work area (S104).
[0031]
Then, the exhaust pipe wall temperature Texp near the air-fuel ratio sensor 42 is estimated based on the intake air temperature THA and the intake air amount GA (S106). The estimation of the exhaust pipe wall temperature Texp is performed as follows.
[0032]
That is, as the intake air amount GA increases, the exhaust amount and the exhaust temperature rise, and the amount of heat applied to the pipe wall of the exhaust passage 36 near the air-fuel ratio sensor 42 increases. On the other hand, when the intake air temperature THA reflecting the outside air temperature decreases, the amount of heat taken from the pipe wall of the exhaust passage 36 near the air-fuel ratio sensor 42 also increases. From this, a map for obtaining the exhaust pipe wall temperature Texp using the intake air amount GA and the intake air temperature THA as parameters is obtained in advance as experimental values, and the exhaust gas is extracted from the intake air temperature THA and the intake air amount GA read in steps S102 and S104. The tube wall temperature Texp is calculated.
[0033]
In addition, the exhaust pipe wall temperature Texp may be obtained by using the intake air temperature THA and the exhaust air temperature THEx detected by the exhaust air temperature sensor 44. That is, at the position of the exhaust gas temperature sensor 44, the detected exhaust gas temperature THEx is attained by the heat transfer between the exhaust gas and the outside air via the tube wall of the exhaust passage 36, so that the exhaust gas passes through the tube wall of the exhaust passage 36. The exhaust pipe wall temperature Texp can be determined from the heat transfer coefficient between the exhaust air and the outside air, the intake air temperature THA, and the exhaust air temperature THEx. In this case, assuming that the heat transfer coefficient is constant, a map for obtaining the exhaust pipe wall temperature Texp using the intake air temperature THA and the exhaust air temperature THEx as parameters may be obtained and used as experimental values.
[0034]
Alternatively, an exhaust pipe wall temperature sensor that detects the temperature of the pipe wall of the exhaust passage 36 near the air-fuel ratio sensor 42 may be provided to directly measure the exhaust pipe wall temperature Texp.
After the exhaust pipe wall temperature Texp is calculated in this way, it is determined whether the exhaust pipe wall temperature Texp is equal to or lower than the determination temperature Tdp (S108). Here, the determination temperature Tdp indicates a dew point of the exhaust gas or a temperature near the dew point, and is set to, for example, “60 ° C.”.
[0035]
Here, if Texp ≦ Tdp (“YES” in S108), then the throttle opening update amount guard value Δθ is set (S110). The throttle opening update amount guard value Δθ limits the rate of increase of the throttle opening TA.
[0036]
The throttle opening TA is adjusted by rotating the throttle valve 26 by the throttle valve motor 24 by the throttle opening control by the ECU 4 so that the throttle opening target value TAt obtained based on the accelerator opening ACCP is obtained. Have been. The amount of power supplied to the throttle valve motor 24 is adjusted so that the rotation amount (° / s) of the throttle valve 26 per unit time at the time of adjusting the throttle opening TA is equal to or less than the throttle opening update guard value Δθ in the opening direction. Adjusted. This limits the throttle opening update amount.
[0037]
The throttle opening update amount guard value Δθ is specifically set based on the exhaust pipe wall temperature Texp as shown in the map of FIG. On the low temperature side of the exhaust pipe wall temperature Texp, the throttle opening update amount guard value Δθ decreases, indicating that the opening speed of the throttle valve 26 decreases as the temperature decreases. Since the opening speed is not limited at 60 ° C. or higher, the throttle opening update amount guard value Δθ is a constant value.
[0038]
Thus, the present process is once ended.
When the throttle opening update amount guard value Δθ is set in this manner (S110), the rotational speed in the opening direction is changed to the throttle opening update amount guard value Δθ by the rotation speed control of the throttle valve 26 separately executed by the ECU 4. Is set as the upper limit.
[0039]
As long as Texp ≦ Tdp (“YES” in S108), the opening speed of the throttle valve 26 is limited by the throttle opening update amount guard value Δθ set according to the value of the exhaust pipe wall temperature Texp.
[0040]
Thereafter, if Texp> Tdp (“NO” in S108), the setting of the throttle opening update amount guard value Δθ is not performed (S110), and the rotation speed of the throttle valve 26 is not limited.
[0041]
Next, a description will be given of the heater energization control process (FIG. 4) for the air-fuel ratio sensor using the exhaust pipe wall temperature Texp obtained in step S106 of the throttle opening speed limiting process (FIG. 2). This process is a process executed after the throttle opening speed limiting process (FIG. 2).
[0042]
When the process is started, it is first determined whether or not Texp ≦ Tdp (S200). This process is the same process as step S108. If Texp ≦ Tdp (“YES” in S200), the vehicle inclination angle Vs detected by the vehicle inclination angle sensor 56 is read (S202). The vehicle inclination angle sensor 56 is configured, for example, by suspending a movable body such as a weight via a wire on an axis fixed to the vehicle, and when the vehicle is parked on an inclined surface such as a sloping road or before and after. The displacement of the movable body when receiving the acceleration is read mechanically or electrically.
[0043]
Next, it is determined whether or not the vehicle inclination angle Vs is equal to or greater than the inclination reference value Ks (S204). The inclination reference value Ks is such that when the vehicle inclines further, the exhaust passage 36 is inclined, and condensed moisture stays in the exhaust passage 36, and the air-fuel ratio sensor 42 may be flooded by a large amount of accumulated water. It represents a certain inclination angle.
[0044]
If Vs <Ks ("NO" in S204), the power supply to the heater in the air-fuel ratio sensor 42 is permitted assuming that there is no risk of being wet (S208). In this case, the air-fuel ratio sensor 42 is heated to the activation temperature by energizing the heater.
[0045]
On the other hand, when Vs ≧ Ks (“YES” in S204), the power supply to the heater in the air-fuel ratio sensor 42 is prohibited because there is a possibility of being wet (S206).
In the above-described configuration, the throttle valve 26 corresponds to intake air amount adjusting means, and the air-fuel ratio sensor 42 is activated by being heated by the heater. Further, steps S102 to S108 of the throttle opening speed limiting process (FIG. 2) correspond to a process as a wet determination unit, and step S110 corresponds to a process as an intake air amount limiting unit.
[0046]
According to the first embodiment described above, the following effects can be obtained.
(I). In a state where there is a possibility that the air-fuel ratio sensor 42 is exposed to water, that is, in a state where the exhaust pipe wall temperature Texp is lower than the dew point temperature and moisture adheres to the exhaust passage 36 near the air-fuel ratio sensor 42 due to condensation of water vapor in the exhaust gas. If it is determined that there is (YES in S108), the rate of increase of the throttle opening TA is limited (S110).
[0047]
As described above, in the state where there is a possibility that the air-fuel ratio sensor 42 is wet, the rate of increase of the intake air amount is limited, so that the exhaust speed does not increase rapidly, and the moisture in the exhaust passage 36 is scattered. Allow for time to evaporate.
[0048]
The ECU 4 does not limit the increase in the amount of intake air, but limits the rate of increase in the amount of intake air. Therefore, the increase in the amount of intake air is possible, and the driver can continue the acceleration operation. It is possible to accelerate. Then, since the exhaust pipe wall temperature Texp steadily rises due to the increase in the intake air amount, the evaporation of the moisture in the exhaust passage 36 ends relatively early. Therefore, there is no great discomfort to the driver.
[0049]
In this manner, by preventing the air-fuel ratio sensor 42 from being wet, it is possible to prevent a failure such as a crack from occurring, and to suppress a sense of discomfort to the driver.
(B). In the present embodiment, in consideration of not only the exhaust flow velocity but also the vehicle inclination, if the vehicle inclination angle Vs ≧ Ks (“YES” in S204), the air-fuel ratio sensor 42 is determined to have a possibility of being wet, and the heater is turned on. Is prohibited (S206). Therefore, even when the vehicle is wet due to the inclination of the vehicle, the air-fuel ratio sensor 42 is not rapidly cooled, and a failure such as a crack can be prevented.
[0050]
[Other embodiments]
(A). The present invention is applicable not only to the gasoline engine of the type in which the fuel injection valve 12 injects the fuel into the intake port 16 as shown in the above-described embodiment, but also to the in-cylinder injection type of gasoline engine in which the fuel is directly injected into the combustion chamber 10. .
[0051]
(B). As the intake air amount adjusting means, a variable valve mechanism (corresponding to a lift amount adjusting means) for adjusting the lift amount of the intake valve 2a without using the throttle valve 26 can also be used. In this case, the guard value in step S110 is a guard value of the lift rate increase rate. Thus, the same effect as in the first embodiment can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an engine and an ECU according to a first embodiment.
FIG. 2 is a flowchart of a throttle opening speed limiting process executed by the ECU.
FIG. 3 is a graph showing a map for obtaining a throttle opening update guard value Δθ from an exhaust pipe wall temperature Texp used in the throttle opening speed limiting process.
FIG. 4 is a flowchart of an air-fuel ratio sensor heater energization control process executed by the ECU.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 2 ... Engine, 2a ... Intake valve, 2b ... Exhaust valve, 4 ... ECU, 10 ... Combustion chamber, 12 ... Fuel injection valve, 14 ... Spark plug, 16 ... Intake port, 20 ... Intake passage, 22 ... Surge tank, 24 ... Throttle valve motor, 26 ... Throttle valve, 28 ... Throttle opening sensor, 30 ... Intake air amount sensor, 31 ... Intake air temperature sensor, 32 ... Exhaust port, 36 ... Exhaust passage, 38 ... First three-way catalytic converter 40: second three-way catalytic converter, 42: air-fuel ratio sensor, 44: exhaust temperature sensor, 46: accelerator pedal, 48: accelerator opening sensor, 50: engine speed sensor, 52: reference crank angle sensor, 54: cooling Water temperature sensor, 56: vehicle inclination angle sensor.

Claims (6)

A protection device for a sensor provided in an exhaust pipe of an internal combustion engine to detect an exhaust component and activated by being heated by a heater,
Wet determination means for determining the possibility of being wet by the sensor,
An internal combustion engine, comprising: an intake air amount limiting unit that limits an increase rate of an intake air amount of the internal combustion engine when the wet determination unit determines that there is a possibility of being wet. Exhaust component detection sensor protection device. 2. The sensor protection device according to claim 1, wherein the sensor is a sensor that detects an oxygen concentration in exhaust gas. 3. The sensor protection device for detecting exhaust components of an internal combustion engine according to claim 1, wherein the water determination unit determines the possibility of water detection of the sensor based on an exhaust gas temperature. The intake air amount limiting means according to any one of claims 1 to 3, wherein the intake air amount limiting means limits the rate of increase of the amount of intake air by limiting the rate of increase of the adjustment amount by the intake air amount adjusting means of the internal combustion engine. Protection device for detecting exhaust components of an internal combustion engine. 5. The sensor protection device according to claim 4, wherein the intake air amount adjusting means is a throttle valve. 5. The sensor protection device according to claim 4, wherein the intake air amount adjusting means is an intake valve lift amount adjusting means.

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