JP4496775B2 - Oxygen sensor heater control device - Google Patents

Description

  The present invention relates to a heater control device for an oxygen sensor, and more particularly to a heater control device for activating an oxygen sensor that detects an oxygen concentration in exhaust gas in an exhaust system of an internal combustion engine.

  When HC, CO and NOx contained in the exhaust gas of an internal combustion engine are purified by a three-way catalyst, in order to maximize the conversion efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen sensor, and the oxygen concentration in the exhaust gas is detected. The actual air-fuel ratio calculated based on the above is used to control the air-fuel ratio to be the stoichiometric air-fuel ratio.

  By the way, in the oxygen sensor used to detect the oxygen concentration in the exhaust gas, it is necessary to raise the ambient temperature of the oxygen sensor to some extent in order to detect the oxygen concentration. With this technology, the temperature of the sensor element is quickly increased, the time until the oxygen sensor is activated (outputs a signal) is shortened, and the purification of exhaust gas is promoted by air-fuel ratio control based on the output of the oxygen sensor. Are known.

On the other hand, if the element temperature of the oxygen sensor is increased too much by the heater, the deterioration of the oxygen sensor is accelerated. For example, as in Patent Document 1, heating is interrupted under the condition that the ambient temperature of the oxygen sensor becomes high. A technique for controlling the heater is also known.
JP-A-10-332628

  However, the conventional technique of intermittently heating the oxygen sensor using a heater basically has a region where heating is performed by the heater (heater ON) depending on the operating state such as engine rotation and load, and heating. A non-performing (heater OFF) area is set, heating is interrupted when the operating state shifts from the heater ON area to the heater OFF area, and heating is performed when the operating state shifts from the heater OFF area to the heater ON area. It is carried out.

  Therefore, after the operation state in which the ambient temperature of the oxygen sensor becomes high continues for a long time and then the operation state shifts to the operation state in which the ambient temperature of the oxygen sensor becomes relatively low, that is, the operation state that has been in the heater OFF region for a long time. When the operation state shifts to the ON region, the oxygen sensor is sufficiently hot while the operation state is in the heater OFF region. Therefore, when the operation state shifts to the heater ON region, oxygen is immediately generated by the heater. When the sensor is heated, the oxygen sensor in a high temperature state is further heated, which may promote deterioration of the oxygen sensor.

Therefore, the oxygen sensor heater control device according to the present invention includes a high load operation duration detecting means for detecting the duration of the engine high load operation state, and the engine operation state is switched from the high load operation to the medium / low load operation. When the engine operating state is high load operation, the heating of the oxygen sensor by the heater is stopped and the engine operating state is changed from high load operation to medium / low load operation. When switching to, the heating start time of the oxygen sensor by the heater is delayed according to the duration of the previous high load operation, and the delay time is less than the preset limit value Rukoto generally set to be longer in proportion to the duration, if the duration is greater than the limit value is set to be substantially constant regardless of the duration in It is characterized.

  According to the present invention, the oxygen sensor in a high temperature state is prevented from being further heated by the heater, deterioration of the oxygen sensor 2 can be effectively suppressed, and the useful life of the oxygen sensor can be increased. .

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a system configuration diagram of an engine according to an embodiment. Air is supplied to the engine 1 via an air cleaner 2, an intake duct 3, a throttle chamber 4, and an intake manifold 5.

  The throttle chamber 4 is configured to open and close the throttle valve 4a with a throttle motor 4a. A fuel injection valve 6 is provided for each cylinder at a branch portion of the intake manifold 5, and an air-fuel mixture is formed by the fuel injected from the fuel injection valve 6. The air-fuel mixture is ignited and burned by spark ignition by the spark plug 7 in the combustion chamber. Each ignition plug 7 is provided with an ignition coil 8. Exhaust gas discharged from the engine 1 is released into the atmosphere through an exhaust manifold 9, a catalytic converter 10, an exhaust duct 11, and a muffler 12.

  The throttle motor 4b, the fuel injection valve 6 and the ignition coil 8 are controlled by an engine control unit 20 (hereinafter referred to as ECU 20) incorporating a microcomputer. Detection signals from various sensors are input to the ECU 20, and the ECU 20 performs arithmetic processing based on these detection signals and outputs a control signal to the fuel injection valve 6 and the like.

  Examples of the various sensors include an air flow meter 21 that detects the amount of intake air to the engine 1 upstream of the throttle chamber 4, a throttle sensor 22 that detects the throttle opening, and a water temperature sensor 23 that detects the cooling water temperature of the engine 1. , A knock sensor 24 for detecting knocking vibration, a crank angle sensor 25 for detecting a clan angle, and an oxygen concentration in the exhaust gas that is closely related to the air-fuel ratio of the combustion mixture upstream of the catalytic converter 10. An oxygen sensor 27 that detects the intake air, an intake air temperature sensor 28 that is provided integrally with the air flow meter 21 and detects the intake air temperature, and the like are provided.

  As shown in FIG. 2, the oxygen sensor 27 has a zirconia tube 30 that protrudes into the exhaust pipe. The oxygen concentration in the exhaust gas outside the zirconia tube 30 and the oxygen concentration in the atmosphere inside An electromotive force corresponding to the difference is generated. A rod-shaped heater 31 for heating the element and activating the oxygen sensor 27 is disposed inside the zirconia tube 30. The oxygen sensor 27 is not limited to a zirconia tube type sensor, and may be a plate type sensor provided with a heater as disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-13107. Further, based on the detection signal of the crank angle sensor 25, the engine speed is calculated in the ECU 20.

  The ECU 20 has a function of controlling energization to the heater 31. Hereinafter, energization control to the heater 31 by the ECU 20 will be described with reference to the flowchart of FIG. In the present embodiment, the functions of the operation state determination means, the high load operation duration detection means, and the operation load switching determination means are provided by the ECU 20 as software as shown in the flowchart of FIG. .

  The flowchart shown in FIG. 3 is executed at predetermined time intervals (for example, every 20 ms) during engine operation. In step (hereinafter simply referred to as S) 2, it is determined whether or not the engine is starting. If the engine is started, the process proceeds to S4. If the engine is already operating, the process proceeds to S10. Here, it is determined whether or not the engine is starting, for example, when the current is flowing to the starter motor for cranking by the driver's engine key operation, the starter motor is determined to be If the crankshaft is rotating while no current is flowing in the engine, it is determined that the engine is not started.

  In S4, the heater OFF flag is set to 0, the process proceeds to S6, energization of the heater 31 is started, and heating of the oxygen sensor 27 by the heater 31 is started. That is, when the heater OFF flag = 0, heating of the oxygen sensor 27 by the heater 31 is started.

  In S8, the delay time continuation counting flag = 0 and the process proceeds to S10.

  In S10, it is determined whether or not the delay time continuation counting flag = 1. If the delay time continuation counting flag = 1, the process proceeds to S37, and the delay time continuation counting flag = 1. If not, the process proceeds to S12.

  In S12, it is determined whether or not the engine 1 is in a high load operation state. If the engine 1 is in a high load operation, the process proceeds to S14, and if the engine 1 is not in a high load operation, that is, medium / low If the load operation is being performed, the process proceeds to S22. Specifically, the determination of the operating state of the engine 1 in S12 is performed by determining the operating state from a map stored in the ECU 20 using the engine speed and the intake air intake amount.

  On the other hand, in S37 as well as S12, it is determined whether or not the engine 1 is in a high load operation state. If the engine 1 is in a high load operation, the process proceeds to S39, and the engine 1 is in a high load operation. If not, the process proceeds to S38.

  In S39, the delay time continuation counting flag = 0 is set, the delay time count is cleared, the timer count is started, and the current routine is ended. The timer count started in S39 is substantially for measuring the duration of the high-load operation state, and is continued until the timer count ends at the timing of S24 described later.

  In S14, it is determined whether or not the heater OFF flag = 1. If the heater OFF flag = 1, the current routine is terminated. If the heater OFF flag = 1 is not satisfied, the process proceeds to S16. .

  In S16, the heater OFF flag is set to 1, the process proceeds to S18, the energization to the heater 31 is stopped, the heating of the oxygen sensor 27 by the heater 31 is interrupted, and the process proceeds to S20. That is, when the heater OFF flag = 1, the oxygen sensor 27 is interrupted by the heater 31.

  In S20, counting by an internal timer in the ECU 20 is started, and the current routine is ended. still. The count of the timer started in S20 substantially measures the duration of the high load operation state and continues until the timer count ends at the timing of S24 described later.

  In S22, it is determined whether or not the heater OFF flag = 1. If the heater OFF flag = 1, the process proceeds to S24. If the heater OFF flag = 1 is not satisfied, the current routine is terminated. . Here, in detail with respect to S22, the case where the heater OFF flag = 1 in S22 is a state in which the heater 31 is not energized regardless of whether the engine is in an intermediate or low load state. In other words, in S22, it is determined whether or not the high load state is switched to the medium / low load state.

  In S24, the timer count started in S20 described above is terminated, and a timer count value is calculated. This timer count value corresponds to the duration of the high-load operation state of the engine.

  In S26, it is determined whether or not the timer count value calculated in S24 is greater than or equal to a predetermined value set in advance. If it is greater than or equal to the predetermined value, the process proceeds to S32, and if it is less than the predetermined value, S28 is performed. Proceed to The timer count value is cleared after the determination process in S26.

  In S28, the heater OFF flag is set to 0, the process proceeds to S30, energization of the heater 31 is started, heating of the oxygen sensor 27 by the heater 31 is started, and this routine is finished. Here, when the duration of the high-load operation state of the engine is short, it is considered that the oxygen sensor 27 is not so hot. Therefore, in S26, when the duration of high load luck is short, that is, when the timer count value is equal to or smaller than the predetermined value, the process proceeds to S28, and heating of the oxygen sensor 27 by the heater 31 is started immediately.

  In S32, the delay time T is calculated based on the timer count value. The delay time T is a value uniquely associated with the timer count value, and is calculated from a table stored in the ECU 20. More specifically, the delay time T is set to be longer in proportion to the timer counter value when the timer count value is not less than the predetermined value in S26 and not more than a preset limit value. When the value is larger than the limit value, the value is substantially constant regardless of the value of the timer counter value. This is because the temperature of the oxygen sensor 27 is considered to be in an equilibrium state and no longer rise in temperature if the oxygen sensor 27 continues for a high load operation state. The limit value is set by experimental adaptation or the like.

  In S34, during the delay time T calculated in S32, the delay time T starts to be counted in order to delay the heating start timing of the oxygen sensor 27 by the heater 31.

  In S36, the delay time continuation counting flag is set to 1, and the process proceeds to S38. That is, the state where the delay time continuation counting flag is “1” means that the start timing of heating of the oxygen sensor 27 by the motor 31 is intentionally delayed regardless of whether the operation state is medium or low load operation. is doing.

  In S38, it is determined whether or not the delay time T calculated in S32 has elapsed. If the delay time T has elapsed, the process proceeds to S40, and if the delay time T has not elapsed, the current routine is performed. Exit.

  In S40, as the delay time T calculated in S32 has elapsed, the delay time continuation counting flag is set to 0, the delay time count is cleared, and the process proceeds to S42.

  In S42, the heater OFF flag is set to 0, the process proceeds to S44, the energization of the heater 31 is started, and the heating of the oxygen sensor 27 by the heater 31 is started.

  FIG. 4 schematically shows the control flow of FIG. 3 described above. Basically, heating of the oxygen sensor 27 by the heater 31 is interrupted when the engine 1 is in a high load operation state (heater OFF), and the oxygen sensor 27 is heated by the heater 31 when the engine 1 is in a medium / low load operation. When the load has shifted from the heater OFF area to the heater ON area, the time during which the load has continuously remained in the immediately preceding heater OFF area, that is, the continuation of the immediately preceding high load operation Heating of the oxygen sensor 27 by the heater 31 is started after the elapse of a delay time T determined according to the time. That is, the heater OFF region is substantially expanded by delaying the heating start timing of the oxygen sensor 27 by the heater 31.

  As described above, in this embodiment, when the temperature of each part of the sensor is in a high temperature state due to high load operation, when the operation state is switched to medium / low load operation, the heater 31 is used. Since the heating of the oxygen sensor 27 by the delay is delayed, the oxygen sensor 27 in the high temperature state is prevented from being further heated by the heater 31, and the deterioration of the oxygen sensor 27 can be effectively suppressed, and the oxygen sensor The service life of 27 can be increased.

  Further, since the oxygen sensor 27 can accurately detect the oxygen concentration if the element temperature is maintained at a certain level or more, the power consumption can be reduced by delaying the heating of the oxygen sensor 27 by the heater 31. Can do.

  In the above-described embodiment, the delay time T is determined according to the duration of the immediately preceding high load operation. However, the oxygen sensor 27 is used by using the duration of the immediately preceding high load operation and the engine speed. The delay time T may be determined according to the estimated temperature of the oxygen concentration sensor 27.

  The technical idea of the present invention that can be grasped from the above embodiment will be listed together with the effects thereof.

  (1) An oxygen sensor that detects the oxygen concentration in the exhaust, a heater that is heated to activate the oxygen sensor, and operating state determination means that determines the engine operating state, and the engine operating state is high When the load is operated, the heating of the oxygen sensor by the heater is interrupted. It has a high load operation duration detection means for detecting the duration of the operation state and an operation load switching judgment means for judging that the engine operation state has been switched from the high load operation to the medium / low load operation. When the state is switched from high load operation to medium / low load operation, the heating start time of the oxygen sensor by the heater is delayed according to the duration of the previous high load operation. Heater controller of an oxygen sensor according to claim Rukoto. Thus, the oxygen sensor in a high temperature state is prevented from being further heated by the heater, deterioration of the oxygen sensor 2 can be effectively suppressed, and the useful life of the oxygen sensor can be increased. Further, since the oxygen sensor can accurately detect the oxygen concentration if the element temperature is maintained at a certain level or more, power consumption can be reduced by delaying the heating of the oxygen sensor by the heater.

  (2) More specifically, the heater control device for the oxygen sensor according to (1) described above uses the duration of the high load operation and the engine speed during the high load operation, and the oxygen at the end of the high load operation. Oxygen sensor temperature estimation means for estimating the sensor temperature. When the engine operating state is switched from high load operation to medium / low load operation, the oxygen sensor temperature estimation means estimates the temperature of the oxygen sensor. Accordingly, the heating start timing of the oxygen sensor by the heater is delayed.

  (3) More specifically, the oxygen sensor heater control device according to the above (1) or (2) includes an engine speed detecting means for detecting the engine speed, and an intake air for detecting the intake air amount of the engine. The operation state determination unit determines the operation state of the engine by using the engine speed and the intake air amount.

Explanatory drawing which shows the system configuration | structure in one Embodiment of this invention. Sectional drawing of an oxygen sensor. The flowchart which shows the flow of control in one Embodiment of this invention. Explanatory drawing which showed the effect | action in one Embodiment of this invention typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine 20 ... Engine control unit 27 ... Oxygen sensor 31 ... Heater

Claims (3)

An oxygen sensor for detecting the oxygen concentration in the exhaust; a heater for heating the oxygen sensor; and an operating state determining means for determining an engine operating state. When the oxygen sensor is heated, the heating of the oxygen sensor by the heater is interrupted and the oxygen sensor is heated by the heater when the engine is operating at a medium or low load.
High load operation duration detection means for detecting the duration of the engine high load operation state;
Having an operation load switching determination means for determining that the engine operating state has been switched from high load operation to medium / low load operation;
When the engine operating state is switched from high load operation to medium / low load operation, the heating start time of the oxygen sensor by the heater is delayed according to the duration of the previous high load operation ,
The delay time is set to be longer in proportion to the duration when the duration is less than or equal to a preset limit value, and when the duration is greater than the limit value, A heater control device for an oxygen sensor, which is set to be substantially constant regardless of the duration . An oxygen sensor for detecting the oxygen concentration in the exhaust; a heater for heating the oxygen sensor; and operating state determining means for determining an engine operating state. In the case of the oxygen sensor heater control device, the heating of the oxygen sensor by the heater is interrupted and the oxygen sensor is heated by the heater when the engine is operating at a medium or low load.
High load operation duration detection means for detecting the duration of the engine high load operation state;
Driving load switching determining means for determining that the operating state of the engine has switched from high load operation to medium / low load operation;
Oxygen sensor temperature estimating means for estimating the temperature of the oxygen sensor at the end of the high load operation using the duration of the high load operation and the engine speed during the high load operation;
When the engine operating state is switched from high load operation to medium / low load operation, the oxygen sensor heating start timing by the heater is delayed according to the temperature of the oxygen sensor estimated by the oxygen sensor temperature estimation means. heater controller of oxygen sensor characterized. The engine speed detecting means for detecting the engine speed and the intake air amount detecting means for detecting the intake air amount of the engine, and the operating state determining means uses the engine speed and the intake air amount to operate the engine. The heater control apparatus for an oxygen sensor according to claim 1 or 2, wherein

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