JP2009091949A - Gas sensor controlling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas sensor controlling device capable of preventing cracking of a sensor element in consideration of the fuel properties. <P>SOLUTION: An engine system comprises a first oxygen sensor 64 including a sensor element 65 exposed to exhaust gas of an engine 2 and a heater for activating the sensor element 65, an ECU 4 for continuing a low temperature mode for a predetermined period from the start of the engine the heater is controlled so that the sensor element 65 is maintained at a temperature lower than a temperature for breaking the element by wetting, and switching the same to a high temperature mode after elapse of the predetermined period where the heater is controlled so that the sensor element 65 reaches its activating temperature, a light emitting element 81 for detecting the alcohol concentration in a fuel as the properties of the fuel to be supplied to the engine 2, and a light receiving element 82. The ECU 4 changes the duration of the low temperature controlling mode according to the alcohol concentration in the fuel. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas sensor control device.

  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, exhaust gas condenses in the exhaust passage after the previous engine stop and water remains in the exhaust passage, or is discharged from the engine after starting. 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 Document 1 discloses a countermeasure technique for such a problem. Patent Document 1 discloses a technique for preventing element breakage of a sensor element by restricting energization to a heater when moisture adheres to the wall surface of an exhaust passage. Specifically, if the temperature of the exhaust passage is below the dew point temperature, the sensor element may be damaged due to water exposure, and energization to the heater is limited. Assuming that the sensor element is not damaged, the restriction on energization to the heater is released.

JP 2001-41923 A

  However, when the properties of the fuel supplied to the internal combustion engine are different, the moisture contained in the fuel is also different, and the amount of moisture generated by the combustion of the fuel is also different. Therefore, the amount of condensed water generated in the exhaust passage varies depending on the properties of the fuel. For example, when using a fuel containing alcohol in gasoline, the amount of condensed water generated in the exhaust passage tends to increase compared to using only gasoline as fuel.

  Therefore, when such a fuel is used, it is necessary to consider the property of the fuel, but the technique disclosed in Patent Document 1 does not take measures from such a viewpoint.

  Accordingly, an object of the present invention is to provide a gas sensor control device that prevents the sensor element from cracking in consideration of the properties of the fuel.

The object is to control a gas sensor including a sensor element that is exposed to exhaust gas of an internal combustion engine and a heating means that activates the sensor element, and to control the heating means so that the temperature is lower than a temperature at which the sensor element is damaged by water. A low temperature control mode that continues for a predetermined period from the start of the engine, a heating control unit that switches to a high temperature control mode that controls the heating unit to reach a temperature at which the sensor element is activated, and a heating control unit that switches to the internal combustion engine Fuel property detection means for detecting the property of the supplied fuel, wherein the heating control means changes the duration of the low temperature control mode according to the detection result of the fuel property detection means. This can be achieved by a gas sensor control device.
With this configuration, element cracking of the sensor element can be prevented in consideration of the properties of the fuel.

The said structure WHEREIN: The said fuel property detection means can employ | adopt the structure which detects the content alcohol content in the said fuel.
With this configuration, the concentration of alcohol contained in the fuel has a causal relationship with the amount of condensed water generated, so changing the duration of the low-temperature control mode according to the alcohol concentration prevents the sensor element from cracking due to water. it can.

The said structure WHEREIN: The said heating control means can employ | adopt the structure which lengthens the said continuation time, so that the content alcohol content in the said fuel is high.
With this configuration, the higher the alcohol concentration, the greater the amount of condensed water generated. Therefore, the sensor element can be prevented from cracking due to water exposure by increasing the duration of the low temperature control mode.

In the above-described configuration, the fuel property detecting unit may include a light emitting element and a light receiving element that receives light emitted from the light emitting element and transmitted through the fuel.
With this configuration, the alcohol concentration can be detected by utilizing the fact that the light transmittance of the fuel varies according to the alcohol concentration.

In the above configuration, the fuel property detection means includes a pressure detection means for detecting the pressure in the cylinder, and a heat quantity estimation for estimating the amount of heat generated by the combustion of the mixed gas in the cylinder based on the detection result of the pressure detection means. It is possible to adopt a configuration including means and fuel injection amount detection means for detecting the fuel injection amount into the cylinder.
With this configuration, the alcohol concentration can be detected by utilizing the fact that the amount of heat generated in the cylinder with respect to the fuel injection amount varies according to the alcohol concentration.

  ADVANTAGE OF THE INVENTION According to this invention, the gas sensor control apparatus which prevents the element crack of a sensor element in consideration of the property of a fuel can be provided.

  Hereinafter, a plurality of embodiments of a gas sensor control device according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing a configuration of an engine system in which a gas sensor control device according to a first embodiment is employed, and is a multi-cylinder in-cylinder injection gasoline engine (hereinafter abbreviated as “engine”) mounted in an automobile. 2 and a schematic configuration of an electronic control unit (hereinafter referred to as “ECU”) 4 thereof. 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 system. 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 and outputs a detection value corresponding to 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, a water temperature sensor 41 that detects the temperature of the coolant of the engine 2, an accelerator opening sensor 56 that detects the amount of depression of the accelerator pedal 44 (accelerator opening ACCP), a crankshaft The engine speed sensor 58, the first oxygen sensor 64, and the second oxygen sensor 70 that detect the engine speed NE from the rotation of the engine 54 output the detected values 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.

  Further, the engine system according to this embodiment includes a fuel tank 80. The fuel stored in the fuel tank 80 is pumped to the fuel injection valve 12 through a pipe (not shown). The fuel tank 80 is provided with a light emitting element 81 and a light receiving element 82 for detecting the alcohol concentration in the fuel. FIG. 2 is a schematic explanatory diagram of the light emitting element 81 and the light receiving element 82.

  The light emitting element 81 and the light receiving element 82 are arranged to face each other with the fuel F interposed therebetween. The light emitting element 81 emits light of a predetermined wavelength toward the fuel F in response to a command from the ECU 4. The light receiving element 82 receives light from the light emitting element 81 that has passed through the fuel F. The light receiving element 82 outputs a value corresponding to the amount of received light to the ECU 4.

  Here, when the fuel F is a mixture of gasoline or light oil with alcohol, it is known that the transmittance of light incident on the fuel F changes based on the alcohol concentration. The ECU 4 can determine the transmittance of the fuel F based on the output value from the light receiving element 82, and can detect the alcohol concentration contained in the fuel F. Specifically, the fuel F obtained by experiments and the like when no alcohol is contained in the fuel is stored in advance in the ROM of the ECU 4 and the fuel F calculated from the output value from the light receiving element 82 is stored. The alcohol concentration contained in the fuel F can be detected by comparing the transmittance of the fuel and the transmittance of the fuel not containing alcohol determined in advance. Therefore, the ECU 4, the light emitting element 81, and the light receiving element 82 function as fuel property detecting means for detecting the property of the fuel, and further detect the alcohol concentration in the fuel. The reason for detecting the alcohol concentration of the fuel F in this way is that the alcohol concentration and the amount of condensed water generated in the exhaust passage 36 have a causal relationship, as will be described in detail later.

  The alcohol includes methanol, ethanol, butanol, propanol and the like. Further, the light emitting element 81 and the light receiving element 82 may be provided, for example, in a pipe communicating from the fuel tank 80 to the fuel injection valve 12.

  Next, the configuration of the first oxygen sensor 64 will be briefly described. FIG. 3 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. 3, it has a housing 69, a laminated sensor element 65, and an outer cover 66a and an inner cover 66b having a double structure provided on the front end side of the housing 69. Although not shown in FIG. 3, 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 briefly described. As shown in FIG. 3, 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 it is discharged out of the outer cover 66a through 68a, a part of the exhaust gas flowing into the inner cover 66b may stay in the inner cover 66b. When the moisture contained in the staying gas comes into contact with the inner wall surface of the inner cover 66b, condensed water may be generated in the inner cover 66b. When the sensor element 65 is maintained at the activation temperature (about 650 ° C.) by the heater and the condensed water gets wet, the sensor element 65 is damaged.

  Next, in order to prevent such damage, a conventional energization control to the heater by the ECU 4 will be described. 4A is a timing chart showing the duty ratio to the heater, and FIG. 4B is a timing chart showing changes in the temperature of the sensor element 65 and the temperature of the inner cover 66b. 4A and 4B are obtained by experiments by the inventor of the present application. In FIG. 4, curve A indicates the duty ratio for the heater, curve B indicates the temperature of the sensor element 65, and curve C indicates the temperature of the inner cover 66b.

  Conventionally, as shown in FIG. 4A, the ECU 4 limits the duty ratio to about 10% from the start of the engine 2 to a predetermined period, and maintains the temperature of the sensor element 65 to be equal to or lower than the predetermined temperature. (P1). The control by the ECU 4 at this time is referred to as a low temperature mode. In addition, a period during which the heater is continuously controlled in the low temperature mode is referred to as a low temperature mode continuing period LP. By executing the control in the low temperature mode, the ECU 4 gradually increases the temperature of the sensor element 65 (P2). Specifically, the temperature of the sensor element 65 is maintained below a temperature (about 250 ° C.) that is damaged by being exposed to water. Similarly, the temperature of the inner cover 66b gradually rises due to exhaust gas or heat received from the heater (P3).

  Next, the ECU 4 raises the temperature of the sensor element 65 to the activation temperature by setting the duty ratio to about 60% from the low temperature mode (P4, P5). The control by the ECU 4 at this time is referred to as a high temperature mode. In addition, a period during which the heater is continuously controlled in the high temperature mode is referred to as a high temperature mode continuing period HP. During the high temperature mode duration HP, immediately after the transition from the low temperature mode, the duty ratio is maintained at about 60% in order to raise the temperature of the sensor element 65 to the activation temperature at an early stage. After reaching the activation temperature, the duty ratio is maintained at about 40 to 20 percent so that the sensor element 65 does not fall below the activation temperature.

  Here, the timing of switching from the low temperature mode to the high temperature mode has conventionally been, for example, the temperature of the coolant at the time of starting the engine, the temperature of the inner cover 66b, the temperature of the wall surface of the exhaust port 32, and the wall surface of the exhaust passage 36. When these temperatures were estimated to have reached temperatures above the dew point, switching from the low temperature mode to the high temperature mode was performed. That is, the heater is controlled in the low temperature mode under the condition where condensed water is generated, and the heater is controlled in the high temperature mode under the condition where condensed water is not generated. For example, when the temperature of the inner cover 66b reaches 100 ° C. or higher, there is no possibility that condensed water is generated on the wall surface of the inner cover 66b, so the control of the heater is switched from the low temperature mode to the high temperature mode. Thereby, the element cracking by the flooding of the condensed water of the sensor element 65 was prevented.

  However, depending on the nature of the fuel supplied to the engine 2, the amount of moisture contained in the exhaust gas differs and the amount of condensed water generated also differs. For example, when a fuel containing alcohol is used, the amount of water contained in the exhaust gas also changes depending on the alcohol concentration. Therefore, the ECU 4 changes the low temperature mode duration LP according to the properties of the fuel. The heater control process executed by the ECU 4 will be specifically described below. The ECU 4 functions as a heating control unit.

  FIG. 5 is a flowchart showing an example of a heater control process executed by the ECU 4. The ECU 4 detects whether or not the ignition is turned on (step S1). If the determination is negative, this process ends. If the determination is affirmative, it can be determined that the engine 2 has started, and the ECU 4 controls the heater in the low temperature mode (step S2). Next, the ECU 4 issues a command to the light emitting element 81, emits light toward the fuel F, and detects the alcohol concentration contained in the fuel F based on the output value from the light receiving element 82 (step S3). . Specifically, the alcohol concentration is detected by a map or the like showing the relationship between the transmittance of the fuel F and the alcohol concentration. This map is obtained in advance by experiments or the like and is stored in the ROM of the ECU 4.

  Next, the ECU 4 determines the low temperature mode duration LP based on a predetermined map stored in the ROM (step S4). FIG. 6 is an example of a map showing the relationship between the alcohol concentration contained in the fuel F and the low temperature mode duration. The higher the alcohol concentration, the longer the low temperature mode duration is set. The reason for this is that the higher the alcohol concentration, the greater the amount of condensed water generated, so that the sensor element 65 can be prevented from cracking due to moisture by increasing the duration of the low temperature control mode. Note that the map shown in FIG. 6 is obtained in advance by experiments or the like.

  Next, the ECU 4 determines whether or not the low temperature mode duration LP determined above has elapsed (step S5). When the determined duration time has elapsed, the ECU 4 switches the heater to control in the high temperature mode (step S6). Thereby, the heater is heated up to the activation temperature. If the determined duration time has not elapsed, the ECU 4 continues the low temperature mode for the heater (step S7). Thereafter, the ECU 4 executes the process of step S5 again, and continues to control the heater in the low temperature mode until the determined duration time has elapsed.

  As described above, the element cracking of the sensor element 65 can be prevented by changing the low temperature mode duration LP in consideration of the properties of the fuel.

  Next, a gas sensor control apparatus according to the second embodiment will be described. FIG. 7 is a configuration diagram of an engine system in which the gas sensor control device according to the second embodiment is employed. In addition, about the location similar to the gas sensor control apparatus which concerns on Example 1, the duplicate description is abbreviate | omitted by using the same code | symbol. As shown in FIG. 7, a pressure sensor 91 for detecting the pressure in the cylinder is provided. The pressure sensor 91 includes a semiconductor element, a piezoelectric element, an optical fiber detection element, or the like, and is provided in a number corresponding to the number of cylinders. In FIG. 7, only one is shown. The pressure sensor 91 is disposed on the cylinder head so that the pressure receiving surface faces the corresponding combustion chamber 10. Further, the detection value of the combustion chamber 10 is output to the ECU 4.

The ECU 4 estimates the amount of heat generated by the combustion of the mixed gas in the cylinder based on the detection value from the pressure sensor 91. Specifically, the ECU 4 estimates using the following formula.

  Here, κ is the specific heat ratio, P is the in-cylinder pressure, V is the in-cylinder volume, and θ is the crank angle. A value obtained by dividing the heat generation amount Q in the cylinder calculated by this equation by the fuel injection amount and the alcohol concentration have a correlation.

  FIG. 8 is a map showing the relationship between the value obtained by dividing the in-cylinder heat generation amount Q by the fuel injection amount and the alcohol concentration. This map is obtained in advance by experiments or the like, and is stored in the ROM of the ECU 4. For example, when the fuel injection amount is the same, the in-cylinder heat generation amount Q varies according to the alcohol concentration. Generally, alcohol has a lower calorific value per volume than gasoline. Accordingly, when the fuel injection amount is the same and the in-cylinder heat generation amount Q is relatively small, the alcohol concentration can be determined to be high, and when the in-cylinder heat generation amount Q is relatively large, The alcohol concentration can be determined as a low concentration. Further, since the ECU 4 controls the fuel injection amount in accordance with the operating state, the alcohol concentration in the fuel can be easily detected by calculating the in-cylinder heat generation amount Q. Therefore, the ECU 4 functions as a heat quantity estimation unit and also functions as a fuel injection amount detection unit that detects the amount of fuel injected into the cylinder. In this way, using the detected alcohol concentration, the ECU 4 changes the duration of the control in the low temperature mode as described above.

  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 by which the gas sensor control apparatus which concerns on Example 1 was employ | adopted. It is typical explanatory drawing of a light emitting element and a light receiving element. It is a schematic diagram of a 1st oxygen sensor. FIG. 4A is a timing chart showing the duty ratio to the heater, and FIG. 4B is a timing chart showing changes in the sensor element temperature and the inner cover temperature. It is the flowchart which showed an example of the control process of the heater which ECU performs. It is an example of the map which showed the relationship between the alcohol concentration contained in fuel, and low temperature mode continuation time. It is a block diagram of the engine system by which the gas sensor control apparatus which concerns on Example 2 was employ | adopted. 4 is a map showing a relationship between a value obtained by dividing the in-cylinder heat generation amount Q by the fuel injection amount and the alcohol concentration.

Explanation of symbols

2 Engine 4 ECU (heating control 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 80 fuel tank 81 light emitting element 82 light receiving element 91 pressure sensor

Claims (5)

A gas sensor comprising a sensor element exposed to exhaust gas of an internal combustion engine and a heating means for activating the sensor element;
The low temperature control mode for controlling the heating means is continued for a predetermined period from the start of the engine so that the temperature of the sensor element is lower than the temperature at which the sensor element is damaged by water, and the heating means is controlled to reach a temperature at which the sensor element is activated. Heating control means for switching to the high temperature control mode after the predetermined period,
Fuel property detection means for detecting the property of the fuel supplied to the internal combustion engine,
The gas sensor control device, wherein the heating control means changes a duration of the low temperature control mode in accordance with a detection result of the fuel property detection means.   The gas sensor control device according to claim 1, wherein the fuel property detection unit detects a concentration of alcohol contained in the fuel.   The gas sensor control device according to claim 2, wherein the heating control unit lengthens the duration as the concentration of alcohol contained in the fuel increases.   4. The gas sensor control device according to claim 2, wherein the fuel property detection unit includes a light emitting element and a light receiving element that receives light emitted from the light emitting element and transmitted through the fuel. 5.   The fuel property detection means includes a pressure detection means for detecting a pressure in the cylinder, a heat quantity estimation means for estimating a heat quantity generated by combustion of the mixed gas in the cylinder based on a detection result of the pressure detection means, The gas sensor control device according to claim 2, further comprising a fuel injection amount detection unit that detects a fuel injection amount into the cylinder.

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