Heater control device

Abstract

To further properly restrain an element crack of a sensor arranged in an exhaust passage of an internal combustion engine.SOLUTION: The control device 100 controls energization of a heater 20h of the second air / fuel ratio sensor 20. The control device 100 executes a process of acquiring the amount of change in impedance of the sensor elements of the second air / fuel ratio sensor 20 before the operation of the internal-combustion engine 10 is stopped, and a process of setting an energization standby time, which is a time from the start of the internal-combustion engine 10 to the start of energization of the heater 20h, based on the acquired amount of change in impedance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heater control device. [Background technology]

[0002] Some sensors provided in the exhaust passage of an internal combustion engine are equipped with a heater to quickly activate the sensor element of the sensor. Here, there may be stagnant water in the exhaust passage due to moisture contained in the exhaust. If the heater is energized when the stagnant water is scattered and adhering to the sensor during engine start-up, the temperature difference between the heating by the heater and the cooling by the adhering water may cause a crack in the sensor element, which is known as element cracking. Therefore, it is preferable to wait until the stagnant water is removed from the exhaust passage after engine start-up before energizing the heater.

[0003] Therefore, in the internal combustion engine described in Patent Document 1, the heater is energized after a predetermined period of time has elapsed since the engine was started. In this internal combustion engine, the timing for energizing the heater is set based on the exhaust system temperature, which is related to the presence or absence of accumulated water in the exhaust passage. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4710615 Summary of the Invention [Problem to be solved by the invention]

[0005] However, since exhaust system temperature is only an indirect way of estimating the amount of accumulated water, there is a risk that the timing for turning on the heater may not be set appropriately, and there is room for improvement in preventing cracking of the sensor element. [Means for solving the problem]

[0006] A heater control device that solves the above problem controls energization of a heater in a sensor provided in an exhaust passage of an internal combustion engine. This control device executes a process of acquiring an amount of change in impedance of a sensor element of the sensor before the internal combustion engine stops, and a process of setting an energization standby time, which is the time from when the internal combustion engine begins to start until energization of the heater, based on the acquired amount of change in impedance. [Effects of the Invention]

[0007] According to the present invention, it is possible to more appropriately prevent element cracking of a sensor provided in an exhaust passage of an internal combustion engine. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an internal combustion engine and its peripheral structure to which a heater control device according to one embodiment of the present invention is applied. [Figure 2] FIG. 2 is a flowchart showing the procedure of processing executed by the control device in the embodiment. [Figure 3] FIG. 3 is a graph showing the operation of the embodiment, where (a) shows the operating state of the internal combustion engine, (b) shows the execution state of the operation for determining stagnant water, (c) shows the impedance of the sensor, and (d) shows the heater current of the sensor. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a heater control device according to one embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. <Configuration of an internal combustion engine> As shown in FIG. 1, an intake passage 11 is connected to an internal combustion engine 10.

[0010] A throttle valve 15 whose passage area is variable is provided in the intake passage 11, and the amount of air taken in through the air cleaner 14 is adjusted by controlling the opening of the throttle valve 15. The amount of air taken in, or intake air amount GA, is detected by an air flow meter 16.

[0011] The air flowing through the intake passage 11 is mixed with fuel injected from a fuel injection valve 17, and then sent to the combustion chamber of the internal combustion engine 10 where it is combusted. An exhaust gas purification catalyst 18 that purifies components in the exhaust gas is provided in the exhaust passage 13 to which the exhaust gas generated by combustion in the combustion chamber is sent. When combustion is performed near the stoichiometric air-fuel ratio, the catalyst 18 oxidizes HC and CO in the exhaust gas and reduces NOx in the exhaust gas, thereby purifying the exhaust gas.

[0012] A first air-fuel ratio sensor 19 is provided upstream of the catalyst 18. A second air-fuel ratio sensor 20 is provided downstream of the catalyst 18. The first air-fuel ratio sensor 19 and the second air-fuel ratio sensor 20 are well-known limiting current oxygen sensors. This limiting current oxygen sensor is a sensor that obtains an output current corresponding to the oxygen concentration in the exhaust gas by incorporating a ceramic layer known as a diffusion-limiting layer in the detection section of a concentration cell-type oxygen sensor. The limiting current oxygen sensor outputs a zero output current when the air-fuel ratio, which is closely related to the oxygen concentration in the exhaust gas, is the stoichiometric air-fuel ratio. Furthermore, as the air-fuel ratio becomes richer, the output current increases in the negative direction, and as the air-fuel ratio becomes leaner, the output current increases in the positive direction. Therefore, the degree to which the air-fuel ratio upstream of the catalyst 18 is lean or rich can be detected based on the output value of the first air-fuel ratio sensor 19. Furthermore, the degree to which the air-fuel ratio downstream of the catalyst 18 is rich or lean can be detected based on the output value of the second air-fuel ratio sensor 20.

[0013] The first air-fuel ratio sensor 19 is provided with a heater 19h that heats the sensor element provided in the first air-fuel ratio sensor 19. The second air-fuel ratio sensor 20 is provided with a heater 20h that heats the sensor element provided in the second air-fuel ratio sensor 20.

[0014] The control device 100 controls the internal combustion engine 10, and operates operating parts of the internal combustion engine 10 such as the throttle valve 15, fuel injection valve 17, and spark plugs to control the torque, exhaust component ratio, and other control variables. The control device 100 is equipped with a CPU and memory composed of a ROM, RAM, and the like, and performs various controls by the CPU executing programs stored in the memory.

[0015] The control device 100 receives detection signals from various sensors, including the air flow meter 16, the first air-fuel ratio sensor 19, the second air-fuel ratio sensor 20, an accelerator sensor that detects the amount of accelerator pedal operation, and a crank angle sensor 21 that detects the engine rotation speed NE, and performs various engine controls according to the operating conditions of the internal combustion engine 10 ascertained from the detection signals from these sensors.

[0016] The control device 100 acquires the impedance imp of the sensor element of the second air-fuel ratio sensor 20. Then, the control device 100 performs feedback control of the heater current, which is the current supplied to the heater 20h, so that the impedance imp becomes a predetermined reference value impb while the internal combustion engine 10 is operating.

[0017] Similarly, the control device 100 performs feedback control on the heater current of the heater 19h for the first air-fuel ratio sensor 19 so that the impedance of the sensor element of the first air-fuel ratio sensor 19 becomes a predetermined reference value while the internal combustion engine 10 is operating.

[0018] Incidentally, if the heater 20h is energized while the second air-fuel ratio sensor 20 is covered in water due to the exhaust gas stirring up accumulated water present in the exhaust passage 13, there is a risk that the sensor element may crack, i.e., element cracking may occur. Such element cracking is likely to occur at engine start-up when the temperature difference between heating by the heater 20h and cooling by the adhering water becomes large.

[0019] Therefore, the control device 100 starts energizing the heater 20h after a predetermined energization wait time td has elapsed since the engine start. By setting this energization wait time td, energization of the heater 20h is suspended until the exhaust flow that occurs after the engine start removes the accumulated water from the exhaust passage 13. This prevents the sensor from being wetted by the accumulated water, thereby suppressing the occurrence of element cracking.

[0020] Here, when the second air-fuel ratio sensor 20 provided in the exhaust passage 13 is exposed to water, the temperature of the sensor element of the second air-fuel ratio sensor 20 drops, and the impedance imp of the sensor element increases. The inventors have found that the more water remains in the exhaust passage 13, the greater the amount of change in the impedance imp. This is because the more water remains in the exhaust passage 13, the greater the amount of water exposure to the sensor. Therefore, in this embodiment, the power-on wait time td is set based on the correlation between the amount of water remaining in the exhaust passage 13 and the amount of change in impedance imp due to the sensor being exposed to water.

[0021] <About the flowchart> 2 shows a processing procedure executed by the control device 100 to set such a power supply waiting time td. Note that this processing is performed before the operation of the internal combustion engine 10 is actually stopped in response to a stop request. For example, when a stop request for the internal combustion engine 10 is made, execution of this processing may be started, and when various conditions are met, including completion of execution of this processing, operation of the internal combustion engine 10 may actually be stopped. In the following, the step number of each processing step will be represented by a number preceded by "S."

[0022] When the series of processes shown in FIG. 2 is started, the control device 100 performs an operation for determining accumulated water (S100). The operation for determining accumulated water is performed to disperse accumulated water in the exhaust passage 13 and cause the second air-fuel ratio sensor 20 to become wet. For example, the control device 100 performs the operation for determining accumulated water by temporarily increasing the intake air amount of the internal combustion engine 10. More specifically, the control device 100 performs the operation for determining accumulated water by temporarily increasing the opening of the throttle valve 15 by a predetermined amount compared to before the operation for determining accumulated water is performed. When the intake air amount increases, the exhaust pulsation occurring in the exhaust passage 13 increases, accelerating the dispersal of accumulated water. Therefore, the second air-fuel ratio sensor 20 is more likely to become wet. Note that when the second air-fuel ratio sensor 20 is wet due to the operation for determining accumulated water, the temperature of the second air-fuel ratio sensor 20 is already sufficiently warmed by the heater 20h, unlike when the sensor is wet immediately after engine start. Therefore, the element cracking due to the temperature difference described above does not occur.

[0023] Next, the control device 100 acquires the impedance imp of the sensor element of the second air-fuel ratio sensor 20 (S110). Next, the control device 100 calculates the impedance change amount Δimp (S120). In the process of S120, the control device 100 calculates a value by subtracting the reference value impb from the impedance imp acquired in the process of S110. Then, the control device 100 substitutes the calculated subtracted value for the impedance change amount Δimp.

[0024] Next, the control device 100 sets the power supply standby time td based on the calculated impedance change amount Δimp (S130). In the process of S130, the control device 100 sets the power supply standby time td so that the larger the impedance change amount Δimp, the longer the power supply standby time td. Note that since the impedance imp changes even during normal operation, the maximum value of the impedance change amount Δimp during such normal operation is obtained in advance and set as the threshold value A. Then, if the calculated impedance change amount Δimp is equal to or smaller than the threshold value A, the power supply standby time td may be set to "0".

[0025] When the process of S130 is completed, the control device 100 ends this process. <Operation of this embodiment> Fig. 3 shows the operation of this embodiment. Fig. 3(a) shows the operating state of the internal combustion engine. Fig. 3(b) shows the state in which the accumulated water determination operation is being performed. Fig. 3(c) shows the impedance imp of the sensor element of the second air-fuel ratio sensor 20. Fig. 3(d) shows the heater current supplied to the heater 20h.

[0026] At time t1, when a request to stop the internal combustion engine 10 is made, the process shown in FIG. 2 is started, and the accumulated water determination operation described above is performed for a predetermined time. When the accumulated water determination operation is performed and the second air-fuel ratio sensor 20 becomes wet, the impedance imp temporarily increases according to the amount of water exposure, which correlates with the amount of accumulated water in the exhaust passage 13. Therefore, an impedance change amount Δimp according to the amount of accumulated water is calculated, and a power supply waiting time td to be applied at the next engine start is set based on the calculated impedance change amount Δimp.

[0027] Thereafter, when the engine is actually stopped at time t2, the current supply to the heater 20h that had been running up until that point is stopped, and the heater current becomes "0". When engine starting is initiated at time t3, power supply to the heater 20h is initiated at time t4, which is the time when the power supply standby time td has elapsed from the timing of engine starting.

[0028] <Effects of this embodiment> (1) The power supply waiting time td, which is the time from when the internal combustion engine 10 starts to when power is supplied to the heater 20h, is set based on the impedance change amount Δimp of the sensor element. The impedance change amount Δimp obtained when the sensor is exposed to water is a value that correlates with the amount of accumulated water in the exhaust passage 13. Therefore, the power supply waiting time td is set with high accuracy according to the amount of accumulated water. Therefore, it is possible to more appropriately prevent element cracking of the sensor element of the second air-fuel ratio sensor 20.

[0029] (2) Since the power supply wait time td can be set with high accuracy, it is possible to suppress delays in activation of the second air-fuel ratio sensor 20, which may be caused by setting an excessive power supply wait time td, for example. Therefore, it is also possible to suppress delays in starting control using the detection value of the second air-fuel ratio sensor 20.

[0030] (3) The above-described operation for determining accumulated water is performed to prevent the second air-fuel ratio sensor 20 from being wetted by accumulated water. Therefore, it is easier to detect a change in impedance imp due to water exposure of the sensor compared to when the operation for determining accumulated water is not performed.

[0031] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0032] In the above embodiment, when a request to stop the internal combustion engine 10 is made, the accumulated water determination operation is performed and the power supply wait time td is set. However, the accumulated water determination operation may not be performed and the power supply wait time td may be calculated at another timing. Such a modification example will be described below.

[0033] First, the impedance change amount Δimp is calculated during normal engine operation. During a fuel cut in which fuel injection from the fuel injection valve 17 is stopped, cooled gas flows through the exhaust passage 13, and this cooled gas also changes the impedance imp. Therefore, it is desirable to calculate the impedance change amount Δimp during engine operation when such a fuel cut is not being executed. Then, for example, when the impedance change amount Δimp is equal to or greater than the threshold A described above, the power supply standby time td is calculated based on the impedance change amount Δimp calculated at that time. The time Te from the time when the power supply standby time td is calculated until the engine is stopped is measured. If the time Te is equal to or greater than the power supply standby time td, it is considered that the removal of accumulated water from the exhaust passage 13 has been completed. Therefore, the heater 20h is powered on simultaneously with the engine start without power supply standby for the heater 20h at the next engine start. On the other hand, if the time Te is shorter than the power supply standby time td, it is considered that the removal of accumulated water from the exhaust passage 13 may not have been completed. Therefore, in this case, when the engine is next started, the heater 20h is energized after the power supply standby time td has elapsed since the engine start. According to this modification, the presence or absence of accumulated water in the exhaust passage 13 when the engine is stopped can be determined by comparing the time Te with the power supply standby time td. Then, based on the determination result, it can be appropriately determined whether or not to standby the power supply to the heater 20h when the engine is next started.

[0034] The setting of the above-mentioned power supply waiting time td may be similarly applied to the power supply control of the heater 19h provided in the first air-fuel ratio sensor 19. The sensor for which the power supply waiting time td is set as described above is the air-fuel ratio sensor provided in the exhaust passage 13, but the present invention may be applied to other sensors equipped with heaters. Examples of other sensors include gas sensors such as a concentration cell type oxygen sensor, a NOx sensor, and a hydrogen sensor. [Explanation of symbols]

[0035] 10...Internal combustion engine 11...Intake passage 13...Exhaust passage 14...Air cleaner 15...Throttle valve 16...Air flow meter 17...Fuel injection valve 18...Catalyst 19...First air-fuel ratio sensor 19h...Heater 20...Second air-fuel ratio sensor 20h...Heater 21...Crank angle sensor 100...Control device

Claims

[Claim 1] A device for controlling energization of a heater included in a sensor provided in an exhaust passage of an internal combustion engine, a process of acquiring an amount of change in impedance of a sensor element of the sensor before the internal combustion engine stops operating; and setting a power supply waiting time, which is the time from when the internal combustion engine is started until when power supply to the heater is started, based on the acquired change in impedance. Heater control device.

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