JP2008286572A - Gas sensor control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor control device capable of preventing damages of a gas sensor due to the submerging of condensed water generated in a cover. <P>SOLUTION: An ECU 4 adopted in an engine system controls a heater so that a sensor element 65 has a temperature lower than that at which a damage is generated due to the submergence of condensed water, under the condition that the condensed water be generated in the inner cover 66b, and controls the heater so that the temperature of the sensor element 65 is raised up to an activation temperature, under the condition that the condensed water not be generated in the inner cover 66b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas sensor control device.

  Conventionally, in an internal combustion engine, gas sensors such as an air-fuel ratio sensor and an oxygen sensor are arranged in an exhaust passage. Such a gas sensor has a sensor element and a heater that activates the sensor element.

  On the other hand, when the internal combustion engine is started or when it is cold, such as immediately after starting, the exhaust gas condenses in the exhaust passage after the previous engine stop in the exhaust passage and water remains, or is discharged from the engine after the start. Condensed water may be generated when the exhaust gas is in contact with the inner wall of the low temperature exhaust passage.

  If the condensed water is applied to the sensor when the sensor is heated by the heater, the sensor element may be cracked. Patent Documents 1 to 4 disclose countermeasures for such problems.

JP-A-8-15213 JP 2001-73827 A JP 2004-101274 A JP 2001-355498 A

By the way, such a gas sensor is known that includes a cover having a vent hole that covers the sensor element and allows exhaust gas to pass therethrough. By covering the sensor element, it is possible to prevent the condensed water from adhering to the sensor element and being damaged.
However, condensed water may be generated due to condensation on the surface of an insulating glass or the like that is disposed in the cover and supports the sensor element. If the condensed water generated in the cover touches the sensor element activated by the heater, the sensor element may be damaged. The techniques disclosed in Patent Documents 1 to 4 are not considered from such a viewpoint.

  Accordingly, an object of the present invention is to provide a gas sensor control device that prevents the gas sensor from being damaged by the water condensate generated in the cover.

  The above object is provided in the exhaust passage of the internal combustion engine, and includes a sensor element, a heating means for activating the sensor element, and a cover that covers the sensor element and is formed with a vent hole, and the heating Whether or not the heating control means for energizing the means, the cooling water temperature detecting means for detecting the temperature of the engine cooling water, and the condition that condensed water is generated in the cover based on the temperature of the engine cooling water. And the heating control means, under the condition that the condensed water is generated in the cover, the heating so that the temperature of the sensor element is less than the temperature at which the sensor element is damaged by the water of the condensed water. The gas sensor control device is characterized in that the heating means is controlled so as to raise the temperature of the sensor element to an activation temperature under a condition in which condensed water cannot be generated in the cover. It can be achieved by.

  With this configuration, when it is determined that the condensate can be generated in the cover, the heating unit is controlled so that the sensor element does not reach a temperature high enough to be damaged by the condensate. . When it is determined that the condition is such that condensed water cannot be generated in the cover, the heating means is controlled to raise the temperature of the sensor element to the activation temperature. Thereby, the sensor element can be prevented from being damaged by the condensate water generated in the cover, and the sensor element can be activated at an early stage.

  ADVANTAGE OF THE INVENTION According to this invention, the gas sensor control apparatus which prevents the damage of a gas sensor by the flooding of the condensed water which generate | occur | produces in a cover can be provided.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram showing a configuration of an engine system according to the present embodiment. A multi-cylinder in-cylinder injecting gasoline engine (hereinafter abbreviated as “engine”) 2 mounted on an automobile and its electronic control unit ( Hereinafter, the schematic configuration of the ECU 4 is referred to as “ECU”. In FIG. 1, the configuration of one cylinder is mainly shown.

The ECU 4 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and controls the operation of the entire engine.
The engine 2 is provided with a fuel injection valve 12 that directly injects fuel into the combustion chamber 10 and an ignition plug 14 that ignites the injected fuel.

  The intake port 16 connected to the combustion chamber 10 is opened and closed by driving an intake valve (not shown). A surge tank 22 is provided in the middle of the intake passage 20 connected to the intake port 16, and a throttle valve 26 whose opening degree is adjusted by a throttle motor 24 is provided upstream of the surge tank 22.

  The intake air amount is adjusted by the opening degree of the throttle valve 26. The throttle opening is detected by a throttle opening sensor 28, and the intake pressure in the surge tank 22 is detected by an intake pressure sensor 30. An air flow meter 21 is disposed in the intake passage 20 to output the intake air amount to the ECU 4.

  The exhaust port 32 connected to the combustion chamber 10 is opened and closed by driving an exhaust valve (not shown). The exhaust passage 36 connected to the exhaust port 32 performs oxidation of unburned components (HC, CO) and reduction of nitrogen oxide (NOx) in the exhaust gas, and has a three-way catalyst having oxygen storage and release functions. A start catalyst 38 is provided. Further, a NOx occlusion reduction catalyst 40 is provided in the exhaust passage 36 downstream of a start catalyst (hereinafter simply referred to as “catalyst”) 38.

  In the exhaust passage 36, a first oxygen sensor 64 is disposed upstream of the catalyst 38, and a second oxygen sensor 70 is disposed between the catalyst 38 and the NOx storage reduction catalyst 40.

  In addition to the throttle opening sensor 28 and the intake pressure sensor 30, the ECU 4 inputs a signal from an accelerator opening sensor 56 that detects the amount of depression of the accelerator pedal 44 (accelerator opening ACCP). Further, the ECU 4 receives signals from an engine speed sensor 58, a first oxygen sensor 64, and a second oxygen sensor 70 that detect the engine speed NE from the rotation of the crankshaft 54, respectively. Further, a water temperature sensor 41 for detecting the engine coolant temperature is provided, and the detected engine coolant temperature is output to the ECU 4.

  The ECU 4 appropriately controls the fuel injection timing, the fuel injection amount, and the throttle opening TA of the engine 2 based on the detection contents from the various sensors described above.

  The ECU 4 sets the fuel injection amount to the output of the first oxygen sensor 64 or the output thereof so that the air-fuel ratio of the exhaust gas flowing into the catalyst 38 becomes the stoichiometric air-fuel ratio in order to enhance the oxidation / reduction ability of the catalyst 38. And the air-fuel ratio feedback control based on the output of the second oxygen sensor 70.

  Next, the configuration of the first oxygen sensor 64 will be briefly described. FIG. 2 is a schematic diagram of the first oxygen sensor 64. The basic structure of the second oxygen sensor 70 is the same as that of the first oxygen sensor 64.

  As shown in FIG. 2, a housing 69a, a laminated sensor element 65 inserted through the housing 69a via an insulator 69b, a double structure outer cover 66a and inner cover 66b provided on the front end side of the housing 69a, Have Although not shown in FIG. 2, the sensor element 65 incorporates a heater (heating means) for raising the temperature of the sensor element 65 to the activation temperature. The operation of the heater is controlled by the ECU 4.

Vent holes 67a and 68a are formed in the outer cover 66a, and vent holes 67b and 68b are formed in the inner cover 66b.
The vent holes 67a and 67b are respectively formed on the outer peripheral side surfaces of the outer cover 66a and the inner cover 66b, and the vent holes 68a and 68b are respectively formed on the lower surfaces of the outer cover 66a and the inner cover 66b.
The exhaust gas flows into the inner cover 66b through the vent holes 67a and 67b, contacts the sensor element 65, and flows so as to be discharged through the vent holes 68b and 68a. By adopting a double pipe structure by the outer cover 66a and the inner cover 66b, the sensor element 65 is prevented from getting wet with condensed water.

Next, problems that may occur in the oxygen sensor having such a cover will be described in detail.
As shown in FIG. 2, the exhaust gas flows into the inner cover 66b through the vent hole 67a and the vent hole 67b. At this time, most of the exhaust gas that flows into the vent hole 68b, Although exhausted to the outside of the outer cover 66a through the 68a, a part of the exhaust gas flowing into the inner cover 66b may stay around the base portion of the sensor element 65. When the moisture contained in the staying gas comes into contact with the lower surface 69c of the insulating glass 69b, condensed water may be generated on the lower surface 69c. When the sensor element 65 is maintained at the activation temperature (about 650 ° C.) by the heater, if the condensed water gets wet, the sensor element 65 is damaged.

  Thus, the sensor element 65 may be damaged by the condensed water generated in the inner cover 66b. However, the ECU 4 determines whether or not the condition for generating condensed water in the inner cover 66b is based on the temperature of the cooling water, and changes the energization state of the heater according to the determination result. This process will be briefly described.

The ECU 4 first determines whether or not the condition is that condensed water is generated in the inner cover 66b.
The conditions under which condensed water is generated in the inner cover 66b are the surfaces of members surrounded by the inner cover 66b including the inner wall of the inner cover 66b (the lower surface 69c of the insulating glass 69b and the housing 69a exposed in the inner cover 66b). The surface temperature is below the upper limit of the dew point temperature under standard atmospheric pressure (below the boiling point of water under standard atmospheric pressure). Specifically, the condition that condensed water is generated in the inner cover 66b refers to a state where the temperature of the inner wall of the inner cover 66b and the lower surface 69c of the insulating glass 69b is 100 ° C. or less. In this state, the exhaust gas touching the inner cover 66b and the lower surface 69c of the insulating glass 69b may cause dew condensation, and condensed water may be generated on the inner wall of the inner cover 66b or the lower surface 69c of the insulating glass 69b.

  The ECU 4 controls the heater so that the sensor element 65 is at a temperature lower than the level at which the sensor element 65 is damaged by the condensate water under conditions where condensed water is generated in the inner cover 66b, and the condensed water is contained in the inner cover 66b. Under the conditions that cannot occur, the heater is controlled so as to raise the temperature of the sensor element 65 to the activation temperature. As a result, when it is determined that the condition is such that condensed water can be generated in the inner cover 66b, the heater is controlled so that the sensor element 65 does not reach a temperature high enough to be damaged by being exposed to condensed water. The If it is determined that the condition is such that condensed water cannot be generated in the inner cover 66b, the heater is controlled so as to raise the temperature of the sensor element 65 to the activation temperature. As a result, it is possible to prevent damage to the sensor element 65 due to flooding of the condensed water generated in the inner cover 66b and to activate the sensor element 65 at an early stage.

  The ECU 4 determines whether or not this condition is satisfied based on the coolant temperature of the engine cooling water. The engine cooling water temperature starts to gradually increase after the engine is started. On the other hand, the temperature of the inner wall of the inner cover 66b and the lower surface 69c of the insulating glass 69b starts to gradually increase due to the amount of heat received from the exhaust gas and the amount of heat received from the heater. Therefore, it can be said that there is a certain correlation between the temperature rise of the engine cooling water and the temperature rise of the inner wall of the inner cover 66b and the lower surface 69c of the insulating glass 69b.

Next, the heater control process executed by the ECU 4 will be specifically described.
FIG. 3 is a flowchart showing an example of a heater control process executed by the ECU 4. FIG. 4 is a chart showing changes in the coolant temperature of the engine, the temperature of the sensor element 65, and the temperature of the inner cover 66b. Note that the chart of FIG. 4 is obtained by an experiment by the inventor of the present application and shows a change in water temperature in a predetermined period from the time of starting the engine. In FIG. 4, a curve A indicates the temperature of the inner cover 66b, a curve B indicates the temperature of the sensor element 65, a curve C indicates the cooling water temperature, and a curve D indicates the duty ratio for the heater. Yes.

  First, the ECU 4 detects the water temperature of the engine cooling water when starting the engine and the current water temperature of the engine cooling water based on the output from the water temperature sensor 41 (step S1). As shown in FIG. 4, the water temperature curve C of the engine cooling water gradually rises as the engine starts.

Next, the ECU 4 calculates a determination value for determining whether or not the condition is such that condensed water is generated in the inner cover 66b (step S2). This determination value is calculated by the following equation.
Judgment value = Water temperature at start-up + (Temperature for rising x Coefficient) …… (1)
The temperature of the rise is the temperature of the rise from the starting temperature to the current temperature. The coefficient is set to be appropriately changeable depending on the mounting position of the first oxygen sensor 64 and the like.

  Next, the ECU 4 determines whether or not the determination value is larger than the reference value (step S3). When the determination value is less than the reference value, the ECU 4 executes low power control on the heater, assuming that the condensed water is generated in the inner cover 66b (step S4, * 1). Specifically, the duty ratio is controlled to about 10%. As a result, the temperature of the sensor element 65 gradually increases (* 2). Further, the curve of the inner cover 66b rises gently (* 3).

  If the determination value is larger than the reference value, the ECU 4 controls the power so that the sensor element 65 reaches the activation temperature with respect to the heater, assuming that the condensed water is not generated in the inner cover 66b. S5, * 4). Specifically, the duty ratio is controlled to about 60%. As a result, the temperature of the sensor element 65 rises gradually and reaches the activation temperature early (* 5). Further, the temperature of the inner cover 66b also rises rapidly (* 6).

  Next, the reference value will be described. This reference value is obtained when the temperature of the inner cover 66b is the upper limit value of the dew point temperature under standard atmospheric pressure (water at The temperature of the sensor element 65 at this time is defined from the temperature of the engine cooling water in a state where the temperature of the sensor element 65 is lower than the temperature at which the sensor element 65 is damaged by water. Specifically, the reference value is the engine cooling in a state where the temperature of the inner cover 66b is increased to 100 ° C. (* 7) and the temperature of the sensor element 65 is less than 300 ° C. (* 8). It is specified from the temperature of water. When the temperature of the inner cover 66b is 100 ° C. or higher, the temperature of the lower surface 69c of the insulating glass 69b is estimated to be 100 ° C. or higher. Therefore, by determining the determination value calculated based on this reference value, it is possible to determine whether or not the current state is a condition for generating condensed water in the inner cover 66b.

  In this way, the ECU 4 controls the heater so that the sensor element 65 is less than the temperature at which the sensor element 65 is damaged by the condensate water under conditions where condensed water is generated in the inner cover 66b (* 1), and the inner cover 66b. Under the condition where condensed water cannot be generated, the heater is controlled to raise the temperature of the sensor element 65 to the activation temperature (* 4). As a result, it is possible to prevent damage to the sensor element 65 due to flooding of the condensed water generated in the inner cover 66b and to activate the sensor element 65 at an early stage.

  Further, since it is determined based on the temperature of the cooling water whether or not the condition is that condensed water is generated in the inner cover 66b, for example, in the case where the inner wall of the exhaust passage is determined based on the temperature. Depending on the fluctuation of the engine operating state, there is a possibility that the temperature once becomes higher than the dew point but again becomes lower than the dew point. However, such a problem can be prevented. That is, by making a determination based on the temperature of the cooling water, the above determination can be made accurately without being affected by fluctuations in the operating state of the engine.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

It is the schematic diagram which showed the structure of the engine system which concerns on a present Example. It is a schematic diagram of a 1st oxygen sensor. It is the flowchart which showed an example of the control process of the heater which ECU performs. It is a chart figure showing changes, such as a temperature of engine cooling water, a temperature of a sensor element.

Explanation of symbols

2 Engine 4 ECU (heating control means, condensed water determination means)
DESCRIPTION OF SYMBOLS 10 Combustion chamber 12 Fuel injection valve 14 Spark plug 16 Intake port 20 Intake passage 22 Surge tank 24 Throttle motor 26 Throttle valve 28 Throttle opening sensor 30 Intake pressure sensor 32 Exhaust port 36 Exhaust passage 38 Catalyst 40 NOx storage reduction catalyst 44 Accelerator pedal 54 Crankshaft 56 Accelerator opening sensor 58 Engine speed sensor 64 First oxygen sensor 65 Sensor element 66a Outer cover 66b Inner cover 70 Second oxygen sensor

Claims (1)

A gas sensor disposed in an exhaust passage of the internal combustion engine, including a sensor element, a heating unit that activates the sensor element, and a cover that covers the sensor element and is formed with a vent hole;
Heating control means for controlling energization of the heating means;
Cooling water temperature detection means for detecting the temperature of the engine cooling water;
Condensed water determination means for determining whether or not it is a condition in which condensed water is generated in the cover based on the temperature of the engine cooling water,
The heating control means controls the heating means so that the temperature of the sensor element is lower than the temperature at which the sensor element is damaged by the exposure of condensed water under the condition that condensed water is generated in the cover. A gas sensor control device, wherein the heating means is controlled so as to raise the temperature of the sensor element to an activation temperature under a condition in which no generation of the gas occurs.

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