JP2011169863A - Heater control device for exhaust gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To monitor an element temperature (a temperature of a sensor element) of an oxygen sensor while reducing costs of the oxygen sensor, and to improve control accuracy of the element temperature. <P>SOLUTION: A switching element 36 is serially connected between the ground and a heater 28 of the oxygen sensor 26, and a voltage detection resistor 37 is connected in parallel with the switching element 36 (that is to say, serially with the heater 28). By focusing attention on that when a resistance value of the heater 28 is changed by temperature change of the heater 28, in response, a heater terminal voltage (an electric potential of an intermediate point 42 between the heater 28 and the voltage detection resistor 37) of when the switching element 36 is in an energization off state is changed, and heater terminal voltage information Vad is changed, the element temperature of the oxygen sensor 26 is estimated on the basis of the heater terminal voltage information Vad detected when the switching element 36 is in the energization off state, and energization of the heater 28 is controlled such that the estimated element temperature becomes a target element temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heater control device for an exhaust gas sensor that controls energization of a heater for heating a sensor element of an exhaust gas sensor provided in an exhaust gas passage of an internal combustion engine to control the temperature of the sensor element.

  In an internal combustion engine that has been electronically controlled in recent years, an exhaust gas sensor (an air-fuel ratio sensor, an oxygen sensor, or the like) that detects an air-fuel ratio, rich / lean, or the like of exhaust gas is installed in an exhaust pipe, and based on the output of the exhaust gas sensor Air-fuel ratio feedback control is performed to feedback-control the fuel injection amount so that the air-fuel ratio of the exhaust gas matches the target air-fuel ratio. In general, an exhaust gas sensor has a low detection accuracy (or cannot be detected) unless the temperature of the sensor element (hereinafter referred to as “element temperature”) is raised to an activation temperature. The sensor element is heated to promote activation of the exhaust gas sensor.

  In the exhaust gas sensor heater control device, for example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2003-148206), a temperature sensor for detecting the element temperature is provided in the exhaust gas sensor, and the temperature sensor detects the temperature. A technique for controlling energization of the heater so that the element temperature becomes the target element temperature has been proposed.

Japanese Patent Laid-Open No. 2003-148206 (page 5, etc.)

  However, in the technique of the above-mentioned Patent Document 1, since it is necessary to provide a temperature sensor for detecting the element temperature in the exhaust gas sensor, the cost of the exhaust gas sensor increases, and there is a demand for cost reduction that is an important technical problem in recent years. There is a disadvantage that it cannot be satisfied. In addition, the exhaust gas sensor that omits the temperature sensor for detecting the element temperature and reduces the cost cannot monitor the element temperature and cannot control the element temperature with high accuracy.

  Therefore, the problem to be solved by the present invention is to provide a heater control device for an exhaust gas sensor that can monitor the element temperature of the exhaust gas sensor and improve the control accuracy of the element temperature while reducing the cost of the exhaust gas sensor. It is to provide.

  In order to solve the above-mentioned problem, the invention according to claim 1 controls the energization of a heater for heating the sensor element of the exhaust gas sensor provided in the exhaust gas passage of the internal combustion engine to control the temperature of the sensor element (hereinafter referred to as “element”). In a heater control device of an exhaust gas sensor having a heater energization control means for controlling a temperature), a voltage detection resistor connected in series with the heater, and a switch means connected in parallel with the voltage detection resistance; When the switch means is in an energized off state, the potential of the intermediate point between the heater and the voltage detection resistor or information correlated therewith (hereinafter collectively referred to as “heater terminal voltage information”) is detected, and the heater terminal voltage information And an element temperature estimating means for estimating the element temperature based on the above.

  In this configuration, when the resistance value of the heater changes due to the temperature change of the heater, the heater terminal voltage (potential at the intermediate point between the heater and the voltage detection resistor) when the switch means is in the energized off state (energization stopped state) accordingly. ) Will change. Therefore, the heater terminal voltage information (for example, the heater terminal voltage, the voltage obtained by dividing the heater terminal voltage by the voltage dividing resistor, etc.) detected when the switch means is turned off is a parameter that accurately reflects the heater temperature. Since the element temperature changes according to the temperature of the heater, the element temperature can be accurately estimated by using the heater terminal voltage information detected when the switch means is in the energized off state. Thereby, since the element temperature of the exhaust gas sensor can be monitored, the element temperature can be accurately controlled by feedback control or the like, and the control accuracy of the element temperature can be improved. Moreover, since it is not necessary to provide a temperature sensor for detecting the element temperature in the exhaust gas sensor, the cost of the exhaust gas sensor can be reduced.

  In this case, the heater energization control means may control the energization of the heater so that the element temperature estimated by the element temperature estimation means becomes the target element temperature. In this way, since the element temperature of the exhaust gas sensor can be quickly controlled to the target element temperature (for example, the activation temperature), the exhaust gas sensor is quickly activated, and the air-fuel ratio feedback based on the output of the exhaust gas sensor Control can be started early, and exhaust emission can be improved.

  Further, as described in claim 3, there is provided a configuration provided with heater deterioration diagnosis means for detecting heater terminal voltage information when the switch means is in an energized off state and performing heater deterioration diagnosis based on the heater terminal voltage information. good. When the resistance value of the heater changes due to the deterioration of the heater, the heater terminal voltage when the switch means is in the energized off state changes accordingly. Therefore, if the deterioration diagnosis of the heater is performed based on the heater terminal voltage information detected when the switch means is in the energized off state, the deterioration of the heater can be diagnosed with high accuracy.

  When the heater deterioration diagnosis unit determines that the heater has deteriorated, the accuracy of estimation of the element temperature based on the heater terminal voltage information may be reduced. The element temperature may be estimated based on the heater terminal voltage information when it is determined that there is no deterioration (the heater is normal). In this way, when it is determined that the heater has deteriorated, estimation of the element temperature based on the heater terminal voltage information is prohibited, and only when it is determined that the heater has not deteriorated (the heater is normal). The element temperature can be estimated based on the voltage information, and the estimation accuracy of the element temperature can be ensured.

FIG. 1 is a schematic configuration diagram of an entire engine control system according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a heater deterioration diagnosis and heater energization control system. FIG. 3 is a flowchart for explaining the flow of processing of the heater deterioration diagnosis routine. FIG. 4 is a flowchart for explaining the flow of processing of the heater energization control routine.

Hereinafter, an embodiment embodying a mode for carrying out the present invention will be described.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 16 whose opening is adjusted by a motor 15 and a throttle opening sensor 17 for detecting the opening (throttle opening) of the throttle valve 16 are provided on the downstream side of the air flow meter 14.

  Further, a surge tank 18 is provided on the downstream side of the throttle valve 16, and an intake pipe pressure sensor 19 for detecting the intake pipe pressure is provided in the surge tank 18. The surge tank 18 is provided with an intake manifold 20 that introduces air into each cylinder of the engine 11, and a fuel injection valve that injects fuel toward the intake port in the vicinity of the intake port of the intake manifold 20 of each cylinder. 21 is attached. An ignition plug 22 is attached to the cylinder head of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by spark discharge of each ignition plug 22.

  On the other hand, a catalyst 24 such as a three-way catalyst for purifying exhaust gas is provided in the exhaust pipe 23 (exhaust gas passage) of the engine 11. An air-fuel ratio sensor 25 (exhaust gas sensor) that outputs a linear air-fuel ratio signal corresponding to the air-fuel ratio of the exhaust gas is provided upstream of the catalyst 24, and the air-fuel ratio of the exhaust gas is theoretically located downstream of the catalyst 24. An oxygen sensor 26 (exhaust gas sensor) is provided in which the output voltage is inverted depending on whether the air-fuel ratio is rich or lean. The air-fuel ratio sensor 25 and the oxygen sensor 26 may include heaters 27 and 28 for heating the sensor elements, respectively (or externally attached).

  A cooling water temperature sensor 29 that detects the cooling water temperature and a knock sensor 30 that detects knocking are attached to the cylinder block of the engine 11. A crank angle sensor 32 that outputs a pulse signal every time the crankshaft 31 rotates by a predetermined crank angle is attached to the outer peripheral side of the crankshaft 31, and the crank angle and the engine are determined based on the output signal of the crank angle sensor 32. The rotation speed is detected.

  Outputs of these various sensors are input to an engine control circuit (hereinafter referred to as “ECU”) 33. The ECU 33 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel injection amount of the fuel injection valve 21 can be determined according to the engine operating state. The ignition timing of the spark plug 22 is controlled. Further, the ECU 33 feeds back the energization duty of the heater 27 of the air-fuel ratio sensor 25 and the heater 28 of the oxygen sensor 26 so that the sensor element temperatures of the air-fuel ratio sensor 25 and the oxygen sensor 26 are maintained in the active temperature range during engine operation. Control.

Next, the structure of the heater deterioration diagnosis and heater energization control system for performing deterioration diagnosis and energization control of the heater 28 of the oxygen sensor 26 will be described with reference to FIG.
A heater 28 of the oxygen sensor 26 is connected to a battery 34 mounted on the vehicle via a relay 35 that is turned on / off by an ignition switch (not shown). A switching element 36 (switch means) is connected in series between the heater 28 and the ground, and the energization of the heater 28 is controlled by turning on / off the switching element 36. In addition, a voltage detection resistor 37 is connected in parallel with the switching element 36 (that is, in series with the heater 28), and a series circuit of two voltage dividing resistors 38 and 39 is connected in parallel with the voltage detection resistor 37.

  When the switching element 36 is energized, the potential at the intermediate point 42 between the heater 28 and the voltage detection resistor 37 is equipotential (0 V) with respect to the ground. Even if the resistance value changes, the effect does not appear in the heater terminal voltage (the potential at the intermediate point 42 between the heater 28 and the voltage detection resistor 37).

  On the other hand, when the switching element 36 is in the energization-off state (energization stop state), the resistance value of the heater 28 changes due to the temperature change of the heater 28 or the deterioration of the heater 28. The heater terminal voltage (the potential at the intermediate point 42 between the heater 28 and the voltage detection resistor 37) changes, and the potential at the intermediate point 43 between the two voltage dividing resistors 38 and 39 (the heater terminal voltage is divided into two voltages). The voltage divided by the resistors 38 and 39) changes. The potential at the intermediate point 43 of the voltage dividing resistors 38 and 39 is input to the A / D converter 41 via the resistor 40, and the output of the A / D converter 41 is detected as heater terminal voltage information Vad.

  The energization off state of the switching element 36 includes a temporary energization off state when the switching element 36 is switched on / off at a predetermined duty ratio during energization control of the heater 28.

  The ECU 33 implements a function as a heater deterioration diagnosis unit 44 (see FIG. 2) by executing a heater deterioration diagnosis routine of FIG. 3 to be described later, and heater deterioration that determines whether the heater 28 of the oxygen sensor 26 has deteriorated or not. Diagnose as follows. When the switching element 36 is in the energized off state, the heater terminal voltage information Vad and the battery voltage Vb (the voltage of the battery 34) are detected, and the deterioration determination value K corresponding to the battery voltage Vb is calculated using a map or the like. Thereafter, the heater terminal voltage information Vad is compared with the deterioration determination value K to determine whether the heater 28 has deteriorated.

  When the resistance value of the heater 28 changes due to the deterioration of the heater 28, the heater terminal voltage (the potential at the intermediate point 42 between the heater 28 and the voltage detection resistor 37) when the switching element 36 is turned off changes accordingly. Thus, the heater terminal voltage information Vad changes. Therefore, if the deterioration diagnosis of the heater 28 is performed based on the heater terminal voltage information Vad detected when the switching element 36 is in the energized off state, the deterioration of the heater 28 can be diagnosed with high accuracy.

  Further, the ECU 33 executes a heater energization control routine of FIG. 4 to be described later, thereby realizing a function as the heater energization control unit 45 (see FIG. 2) and controlling the energization of the heater 28 of the oxygen sensor 26. Control is performed as follows. When the heater deterioration diagnosis unit 44 determines that the heater 28 has not deteriorated (the heater 28 is normal) and the switching element 36 is in the energized off state, the heater terminal voltage information Vad and the battery voltage Vb are detected, and the heater terminal voltage information Vad is detected. Based on the battery voltage Vb, the temperature Test of the sensor element of the oxygen sensor 26 (hereinafter referred to as “element temperature”) is estimated. Thereafter, the energization of the heater 28 is controlled so that the estimated element temperature Test becomes the target element temperature Ttrg.

  When the resistance value of the heater 28 changes due to the temperature change of the heater 28, the heater terminal voltage (the potential at the intermediate point 42 between the heater 28 and the voltage detection resistor 37) when the switching element 36 is in an energized off state changes accordingly. Thus, the heater terminal voltage information Vad changes. Therefore, the heater terminal voltage information Vad detected when the switching element 36 is in the energized off state is a parameter that accurately reflects the temperature of the heater 28, and the element temperature changes according to the temperature of the heater 28. If the heater terminal voltage information Vad detected when is turned off, the element temperature Test can be accurately estimated.

  The processing contents of the heater deterioration diagnosis routine of FIG. 3 and the heater energization control routine of FIG. 4 executed by the ECU 33 will be described below.

[Heater deterioration diagnosis routine]
The heater deterioration diagnosis routine shown in FIG. 3 is repeatedly executed at a predetermined cycle while the ECU 33 is turned on, and serves as a heater deterioration diagnosis means in the claims. When this routine is started, first, at step 101, it is determined whether or not the switching element 36 that controls the energization of the heater 28 is in an energized off state. If it is determined in step 101 that the switching element 36 is not in the energized off state (the switching element 36 is in the energized on state), this routine is terminated without performing the processing from step 102 onward.

  On the other hand, if it is determined in step 101 that the switching element 36 is in the energized off state, the process proceeds to step 102 and the heater terminal voltage information Vad (output of the A / D converter 41) and the battery voltage Vb are read. .

  Thereafter, the process proceeds to step 103, where a deterioration determination value K corresponding to the battery voltage Vb is calculated using a map or the like. Here, since the heater terminal voltage increases as the battery voltage Vb increases, the map of the deterioration determination value K is set so that the deterioration determination value K increases as the battery voltage Vb increases.

  It should be noted that the deterioration determination value K corresponding to the battery voltage Vb and the heater temperature Th (heater 28 temperature) may be calculated using a map or the like. Here, the heater terminal voltage increases as the battery voltage Vb increases, and the resistance value of the heater 28 increases and the heater terminal voltage decreases as the heater temperature Th increases. The deterioration determination value K increases as the voltage Vb increases, and the deterioration determination value K decreases as the heater temperature Th increases.

  Thereafter, the process proceeds to step 104, where it is determined whether or not the heater terminal voltage information Vad is smaller than the deterioration determination value K. As a result, when it is determined that the heater terminal voltage information Vad is smaller than the deterioration determination value K, it is determined that the heater 28 has deteriorated and the resistance value of the heater 28 has become abnormally large, and the process proceeds to step 105. It is determined that the heater 28 has deteriorated. In this case, the abnormality flag is set to ON and a warning lamp (not shown) provided on the instrument panel of the driver's seat is turned on, or a warning display section (not shown) of the driver's seat instrument panel is provided. ) Is displayed to warn the driver, and the abnormality data (abnormality code or the like) is stored in a rewritable nonvolatile memory such as a backup RAM (not shown) of the ECU 33 (even when the ECU 33 is powered off). This routine is terminated.

  On the other hand, if it is determined in step 104 that the heater terminal voltage information Vad is greater than or equal to the deterioration determination value K, the process proceeds to step 106, where it is determined that the heater 28 has not deteriorated (the heater 28 is normal). The abnormality flag is kept OFF, and this routine is terminated.

[Heater energization control routine]
The heater energization control routine shown in FIG. 4 is repeatedly executed at a predetermined cycle while the ECU 33 is powered on, and serves as a heater energization control means in the claims. When this routine is started, first, in step 201, it is determined whether or not the heater 28 is not deteriorated (the heater 28 is normal) based on the diagnosis result of the heater deterioration diagnosis routine of FIG.

  If it is determined in step 201 that the heater 28 has deteriorated, it is determined that the estimation accuracy of the element temperature Test based on the heater terminal voltage information Vad may be reduced, and the processes in and after step 202 are performed. By ending this routine without performing it, the estimation of the element temperature Test based on the heater terminal voltage information Vad is prohibited.

  On the other hand, if it is determined in step 201 that the heater 28 has not deteriorated (the heater 28 is normal), it is determined that the estimated accuracy of the element temperature Test based on the heater terminal voltage information Vad can be secured, and the heater terminal The estimation of the element temperature Test based on the voltage information Vad is permitted, and the processing after step 202 is executed as follows.

  First, in step 202, it is determined whether or not the switching element 36 that controls the energization of the heater 28 is in an energized off state. If it is determined in step 202 that the switching element 36 is not in the energization-off state (the switching element 36 is in the energization-on state), this routine is terminated without performing the processing after step 203.

  On the other hand, if it is determined in step 202 that the switching element 36 is in the energized off state, the process proceeds to step 203, where the heater terminal voltage information Vad (output of the A / D converter 41) and the battery voltage Vb are read. .

  Thereafter, the process proceeds to step 204, where the resistance value R of the heater 28 is calculated based on the heater terminal voltage information Vad and the battery voltage Vb. Then, the process proceeds to step 205, where the element temperature Test is determined based on the resistance value R of the heater 28. It is calculated (estimated) using a map or mathematical formula. The element temperature Test map or mathematical expression, for example, defines the relationship between the resistance value R (heater 28 temperature information) of the heater 28 and the element temperature Test, and is based on test data, design data, or the like in advance. It is created and stored in the ROM of the ECU 33. The processing of these steps 201 to 205 serves as element temperature estimation means in the claims.

  Note that the element temperature Test may be directly calculated (estimated) using a map or a mathematical formula based on the heater terminal voltage information Vad and the battery voltage Vb. Further, when the battery voltage Vb is substantially constant, the element temperature Test may be calculated (estimated) based on only the heater terminal voltage information Vad using a map or a mathematical expression.

  Thereafter, the process proceeds to step 206, and the target element temperature Ttrg is calculated based on the engine operating state (for example, the water temperature at the start, the elapsed time after the start, etc.). Thereafter, the process proceeds to step 207, where the energization duty Duty of the heater 28 is calculated by PID control or the like so that the deviation between the target element temperature Ttrg and the element temperature Test is small. The on / off of the switching element 36 is controlled so as to energize 28. As a result, the energization duty Duty of the heater 28 is feedback-controlled so that the estimated element temperature Test becomes the target element temperature Ttrg.

  In the present embodiment described above, when the resistance value of the heater 28 changes due to the temperature change of the heater 28, the heater terminal voltage (the heater 28 and the voltage detection resistor 37 between the heater 28 and the voltage detection resistor 37) when the switching element 36 is turned off accordingly. Focusing on the fact that the heater terminal voltage information Vad changes as the potential of the intermediate point 42 changes, the element temperature Test is estimated based on the heater terminal voltage information Vad detected when the switching element 36 is in the energized off state. As a result, the element temperature Test can be estimated with high accuracy. Thereby, since the element temperature of the oxygen sensor 26 can be monitored, the element temperature can be accurately controlled by feedback control or the like, and the control accuracy of the element temperature can be improved. In addition, since it is not necessary to provide the oxygen sensor 26 with a temperature sensor that detects the element temperature, the cost of the oxygen sensor 26 can be reduced.

  Furthermore, in this embodiment, since the energization duty of the heater 28 is feedback-controlled so that the estimated element temperature Test becomes the target element temperature Ttrg, the element temperature of the oxygen sensor 26 is quickly adjusted to the target element temperature (for example, the active element temperature). Temperature), the oxygen sensor 26 can be activated quickly, air-fuel ratio feedback control based on the output of the oxygen sensor 26 can be started early, and exhaust emission can be improved.

  Further, in this embodiment, when the resistance value of the heater 28 changes due to the deterioration of the heater 28, the heater terminal voltage (the intermediate point between the heater 28 and the voltage detection resistor 37) when the switching element 36 is turned off accordingly. 42), the heater terminal voltage information Vad changes, and the heater terminal voltage information Vad detected when the switching element 36 is in the energized off state is compared with the deterioration determination value K. Therefore, the deterioration of the heater 28 can be accurately diagnosed.

  Further, in this embodiment, when it is determined that the heater 28 is deteriorated, it is determined that the estimation accuracy of the element temperature Test based on the heater terminal voltage information Vad may be reduced, and the heater terminal voltage information Vad is determined. Based on the heater terminal voltage information Vad, the element temperature Test is estimated only when it is determined that the heater 28 is not deteriorated (the heater 28 is normal). The estimation accuracy of the temperature Test can be ensured.

  In the above embodiment, the heater terminal voltage information Vad that changes in accordance with the heater terminal voltage is detected, and the element temperature is estimated and the deterioration diagnosis of the heater 28 is performed based on the heater terminal voltage information Vad. The heater terminal voltage may be directly detected, and the element temperature may be estimated or the heater 28 may be deteriorated based on the heater terminal voltage.

  In the above embodiment, the present invention is applied to the estimation of the element temperature of the oxygen sensor 26 and the deterioration diagnosis of the heater 28 of the oxygen sensor 26. However, the estimation of the element temperature of the air-fuel ratio sensor 25 and the heater 27 of the air-fuel ratio sensor 25 are performed. The present invention may be applied to the deterioration diagnosis.

  In addition, the present invention is not limited to the intake port injection type engine as shown in FIG. 1, but includes an in-cylinder injection type engine, and both an intake port injection fuel injection valve and an in-cylinder injection fuel injection valve. It can also be applied to dual-injection engines.

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 16 ... Throttle valve, 21 ... Fuel injection valve, 22 ... Spark plug, 23 ... Exhaust pipe (exhaust gas passage), 26 ... Oxygen sensor (exhaust gas sensor), 28 ... Heater 33 ... ECU (heater energization control means, element temperature estimation means, heater deterioration diagnosis means) 34 ... Battery 36 ... Switching element (switch means) 37 ... Voltage detection resistor 44 ... Heater deterioration diagnosis section 45 ... Heater energization controller

Claims (4)

An exhaust gas sensor having heater energization control means for controlling energization of a heater for heating a sensor element of an exhaust gas sensor provided in an exhaust gas passage of an internal combustion engine to control the temperature of the sensor element (hereinafter referred to as “element temperature”) In the heater control device of
A voltage detection resistor connected in series with the heater;
Switch means connected in parallel with the voltage detection resistor;
When the switch means is in an energized off state, a potential at an intermediate point between the heater and the voltage detection resistor or information correlated therewith (hereinafter collectively referred to as “heater terminal voltage information”) is detected, and the heater terminal A heater control device for an exhaust gas sensor, comprising: an element temperature estimating means for estimating the element temperature based on voltage information.   The heater control apparatus for an exhaust gas sensor according to claim 1, wherein the heater energization control unit controls energization of the heater so that the element temperature estimated by the element temperature estimation unit becomes a target element temperature.   2. A heater deterioration diagnosis unit that detects the heater terminal voltage information when the switch unit is in an energized off state, and performs a deterioration diagnosis of the heater based on the heater terminal voltage information. Or the heater control apparatus of the exhaust gas sensor of 2.   The element temperature estimation means includes means for estimating the element temperature based on the heater terminal voltage information when the heater deterioration diagnosis means determines that the heater is not deteriorated. A heater control device for the exhaust gas sensor described.

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