JP3622584B2 - Oxygen concentration detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxygen concentration detection device, and more particularly to an oxygen concentration detection device that prevents element cracking of an air-fuel ratio sensor due to scattering of water adhering to an exhaust pipe wall surface.
[0002]
[Prior art]
In recent air-fuel ratio control of an engine, an air-fuel ratio sensor and a catalyst are arranged in the exhaust system of the engine, and in order to purify harmful components (HC, CO, NOx, etc.) in the exhaust gas to the maximum with the catalyst, Feedback control is performed so that the exhaust air-fuel ratio of the engine detected by the fuel ratio sensor becomes a target air-fuel ratio, for example, the stoichiometric air-fuel ratio. As this air-fuel ratio sensor, a λ-type oxygen sensor (O) having a Z characteristic for determining whether the exhaust air-fuel ratio of the engine is rich or lean from the oxygen concentration contained in the exhaust gas discharged from the engine₂And a limiting current type oxygen concentration detecting element that outputs a limiting current in proportion to the oxygen concentration contained in the exhaust gas exhausted from the engine. The limiting current type oxygen concentration detection element detects the exhaust air / fuel ratio of the engine in a wide area and linearly from the oxygen concentration, and improves the air / fuel ratio control accuracy, or the rich / theoretical air / fuel ratio (stoichi) / lean wide area sky. This is useful for controlling the exhaust air-fuel ratio of the engine to the target air-fuel ratio between the fuel ratios.
[0003]
These air-fuel ratio sensors, that is, O₂It is essential that the sensor and the limiting current type oxygen concentration detection element be kept in an active state in order to maintain the detection accuracy of the air-fuel ratio.₂The heaters attached to the sensor or the limiting current type oxygen concentration detecting element are energized from the time of engine startup to heat them, and the heaters are energized to be activated early and maintain their active state.
[0004]
The heater control device for an air-fuel ratio sensor disclosed in Japanese Patent Application Laid-Open No. Hei 8-278279 has a total power, that is, 100% until the heater temperature reaches a predetermined temperature for early activation of elements of the air-fuel ratio sensor at the initial stage of energization of the heater. Electric power is supplied to the heater at a duty ratio. When the heater temperature reaches a predetermined temperature, electric power corresponding to the heater temperature is supplied to the heater. When the element temperature of the air-fuel ratio sensor reaches the predetermined temperature, the electric power corresponding to the element temperature of the air-fuel ratio sensor is supplied. Supply power to the heater.
[0005]
[Problems to be solved by the invention]
However, in the heater control device of the air-fuel ratio sensor disclosed in the above-mentioned JP-A-8-278279, when the engine is cold started, moisture condensed by the catalyst provided upstream in the exhaust pipe is attached to the exhaust pipe wall surface, When the air-fuel ratio sensor is electrically heated to quickly activate the air-fuel ratio sensor at the time of cold start of the engine and the element temperature of the air-fuel ratio sensor is raised, moisture adhering to the exhaust pipe wall surface is scattered and disposed downstream of the catalyst in the exhaust pipe. The air-fuel ratio sensor element in the protective cover gets wet by passing through a small hole in the protective cover attached to the exhaust pipe so as to surround the air-fuel ratio sensor, and the air-fuel ratio sensor element is rapidly cooled. There is a problem that the temperature difference from the element temperature of the air-fuel ratio sensor increases abruptly, and the element of the air-fuel ratio sensor is cracked due to so-called thermal shock.
[0006]
Therefore, the present invention solves the above-described problem and prevents element cracking of the air-fuel ratio sensor due to thermal shock caused by water exposure of the air-fuel ratio sensor element at the time of cold start of the engine or preheating of the air-fuel ratio before start-up. An object of the present invention is to provide an oxygen concentration detection device.
[0007]
[Means for Solving the Problems]
An oxygen concentration detection apparatus according to the present invention that solves the above-described problem is an air-fuel ratio sensor provided in an exhaust pipe of an internal combustion engine, a heater that heats the air-fuel ratio sensor, and an air-fuel ratio sensor that is at an activation temperature. A heater energization means for energizing the heater;Detecting means for detecting the temperature of the outside air flowing into the intake pipe of the internal combustion engine; first calculating means for calculating a first exhaust temperature downstream of the catalyst provided downstream of the air-fuel ratio sensor in the exhaust pipe of the internal combustion engine; Based on the outside air temperature and the first exhaust temperature, a second calculating means for calculating a second exhaust temperature around the air-fuel ratio sensor, and the air-fuel ratio from the second exhaust temperature and the heat transfer coefficient of the exhaust pipe. Based on the exhaust pipe temperature calculating means for calculating the temperature of the exhaust pipe around the sensor, and the temperature of the exhaust pipe calculated by the exhaust pipe temperature calculating means,A determination means for determining whether moisture has adhered to the wall surface of the exhaust pipe; and when the determination means has determined that moisture has adhered to the wall surface of the exhaust pipe, And an energization restricting means for restricting energization.
[0008]
With the above configuration, when it is determined that moisture has adhered to the wall surface of the exhaust pipe, energization to the heater is restricted, so that the element of the air-fuel ratio sensor is prevented from being wetted and element cracking due to thermal shock is prevented. Here, when moisture adheres to the wall surface of the exhaust pipe, this includes that the possibility that moisture adheres is high.
In addition, with the above configuration, moisture adheres to the wall surface of the exhaust pipe because water vapor in the exhaust pipe is condensed, and this is determined from the exhaust pipe temperature, so it is determined that moisture has adhered to the wall surface of the exhaust pipe. Improves accuracy.
The oxygen concentration detection device includes a flow rate suppression unit that suppresses the flow rate of the exhaust gas of the internal combustion engine when the determination unit determines that moisture is attached to the wall surface of the exhaust pipe.
[0009]
With the above configuration, the flow rate of the exhaust gas is suppressed, so that the scattering of water adhering to the wall surface of the exhaust pipe is suppressed, the water exposure to the elements of the air-fuel ratio sensor is reduced, and the probability of element cracking due to thermal shock is reduced.To do.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an embodiment of an oxygen concentration detection apparatus according to the present invention. In FIG. 1 and subsequent figures, the same components are denoted by the same reference numerals. An air / fuel ratio (A / F) sensor 1 that is disposed in an exhaust pipe of an internal combustion engine (not shown) and detects an exhaust air / fuel ratio of the engine includes an air / fuel ratio sensor element (hereinafter referred to as a sensor element) 2 and a heater 4. A voltage is applied to the sensor element 2 from an air-fuel ratio (A / F) sensor circuit (hereinafter referred to as a sensor circuit) 3, and electric power is supplied to the heater 2 from the battery 5 via the heater control circuit 6. The sensor circuit 3 receives an analog applied voltage from an air-fuel ratio control unit (A / FCU) 10 formed of a microcomputer via a low-pass filter (LPF) 7 and applies it to the sensor element 2.
[0012]
The A / FCU 10 forms part of the electronic control unit (ECU) 100 together with the sensor circuit 3, the heater control circuit 6 and the LPF 7, and converts digital data into a rectangular analog voltage by a D / A converter provided therein. After that, it outputs to the sensor circuit 3 through the LPF 7. The LPF 7 outputs a smoothed signal from which a high-frequency component of the rectangular analog voltage signal is removed, and prevents an error in detecting the output current of the sensor element 2 due to high-frequency noise. As the voltage of the annealing signal is applied to the sensor element 2, the A / FCU 10 supplies the current flowing through the sensor element 2 that changes in proportion to the oxygen concentration in the gas to be detected, that is, to the sensor element 2 at that time. The applied voltage is detected. The A / FCU 10 is provided with an A / D converter in order to detect these currents and voltages, and these A / D converters are analog voltages and sensors corresponding to the current flowing from the sensor circuit 3 to the sensor element 2. The voltage applied to the element 2 is received and converted into digital data.
[0013]
The air-fuel ratio sensor 1 cannot use its output for air-fuel ratio control unless the sensor element 2 is activated. For this reason, the A / FCU 10 supplies power from the battery 5 to the heater 4 built in the sensor element 2 when the engine is started to energize the heater 4, activates the sensor element 2 early, and activates the sensor element 2. Supplies power to the heater 4 to maintain its active state. The voltage of the battery 5 is converted into digital data by an A / D converter provided in the A / FCU 10.
[0014]
However, focusing on the fact that the resistance of the sensor element 2 depends on the temperature of the sensor element 2, that is, the resistance of the sensor element 2 attenuates as the sensor element temperature increases, the temperature at which the resistance of the sensor element 2 maintains the active state of the sensor element 2 Control is performed to maintain the temperature of the sensor element 2 at a target temperature, for example, 700 ° C., by supplying electric power to the heater 4 so that the resistance value corresponds to, for example, 30Ω. The air-fuel ratio control unit (A / FCU) 10 includes an A / D converter that receives analog voltage corresponding to the voltage and current of the heater 4 from the heater control circuit 6 that heats the sensor element 2 and converts the analog voltage into digital data. Provided. Using these digital data, for example, the resistance value of the heater 4 is calculated, power is supplied to the heater 4 according to the operating state of the engine based on the calculated resistance value, and overheating (OT) of the heater 4 is prevented. Thus, the temperature of the heater 4 is controlled. In the embodiment of the present invention, a limiting current type oxygen concentration detection element is used as the air-fuel ratio sensor 1. However, the present invention is not limited to this, and the air-fuel ratio sensor 1 is a λ-type oxygen sensor (O) having a Z characteristic for determining whether the air-fuel ratio is rich or lean.₂It can also be applied to the case where a sensor is used.
[0015]
The air-fuel ratio control unit (A / FCU) 10 includes, for example, a CPU, ROM, RAM, B (battery backup). A RAM, an input port, an output port, an A / D converter, and a D / A converter are provided to perform heater control of an air-fuel ratio sensor 1 of the present invention described later. Further, a water temperature sensor (not shown) for detecting the cooling water temperature THW of the engine is connected to the A / D converter in the A / FCU 10, and the CPU reads THW at a predetermined cycle.
[0016]
Here, a cup-type air-fuel ratio sensor in which element cracking of the air-fuel ratio sensor occurs during cold start will be described below.
FIG. 2 is a sectional view of the cup-type air-fuel ratio sensor. The sensor main body 20 of the cup-type air-fuel ratio sensor has a diffusion resistance layer 21 having a cup-shaped cross section, and this diffusion resistance layer 21 is fitted into a mounting hole portion of an engine exhaust pipe 27 at an opening end 21a. It is fixed. The diffusion resistance layer 21 is formed by a plasma spraying method such as ZrO2. The sensor body 20 has a solid electrolyte layer 22, and the solid electrolyte layer 22 is formed of an oxygen ion conductive oxide sintered body and an inner peripheral wall of the resistance diffusion layer 21 through an exhaust gas side electrode layer 23 having a cup-shaped cross section. It is fitted and fixed uniformly. On the inner surface of the solid electrolyte layer 22, an atmosphere-side electrode layer 24 is uniformly fixed in a cross-sectional cup shape. In such a case, both the exhaust gas side electrode layer 23 and the atmosphere side electrode layer 24 are formed so as to be sufficiently porous by chemical plating or the like with a noble metal having high catalytic activity such as platinum (Pt). The area and thickness of the exhaust gas side electrode layer 23 are 10 to 100 mm.²And about 0.5 to 2.0 μm. On the other hand, the area and thickness of the atmosphere side electrode layer 24 is 10 mm.²As described above, the thickness is about 0.5 to 2.0 μm. The sensor body 20 is surrounded by a protective cover 28. The protective cover 28 is provided in order to ensure the heat insulation of the sensor body 20 while preventing direct contact with the exhaust gas of the sensor body 20. The protective cover 28 is provided with a large number of small holes for communicating the inside and outside of the cover.
[0017]
Since it is necessary to supply a large amount of power to the heater 26 in order to heat the sensor body 20 early when the engine is cold-started, according to the prior art, power is supplied from the battery 5 to the heater 26 at a duty ratio of 100%. . However, when the moisture condensed by the catalyst provided upstream in the exhaust pipe 27 is accumulated at the bottom of the exhaust pipe 27 and the exhaust system at the time of cold start of the engine is not yet warm, this condensed water is combined with the exhaust gas. As a result, the sensor body 20 scatters and passes through the small hole of the protective cover 28 to contact the sensor body 20 to rapidly cool the sensor body 20. As a result, the sensor body 20 is cracked.
[0018]
FIG. 3 is a block diagram of an internal combustion engine equipped with the oxygen concentration detection apparatus shown in FIG. In FIG. 3, a throttle valve 33 is provided in an intake passage 31 of an internal combustion engine (hereinafter simply referred to as an engine) 30 on the downstream side of the air cleaner 32, and the throttle valve 33 is provided at one end of the shaft of the throttle valve 33. A throttle motor 34 that is an actuator for driving the actuator 33 is provided, and a throttle opening sensor 35 that detects the opening of the throttle valve 3 is provided at the other end. That is, the throttle valve 33 of this embodiment is an electronically controlled throttle (hereinafter simply referred to as an electronic throttle) that is driven to open and close by a throttle motor 34. In the electronic throttle, when the opening command value of the throttle valve 33 is input, the throttle motor 34 causes the throttle valve 33 to follow the command opening in response to the command value.
[0019]
An intake air temperature sensor 36 is provided between the throttle valve 33 and the air cleaner 32 in the intake passage 31, and a surge tank 37 is provided downstream of the throttle valve 33. Further, on the downstream side of the surge tank 37, a fuel injection valve 38 for supplying pressurized fuel from the fuel supply system to the intake port is provided for each cylinder. The output of the throttle opening sensor 35 and the output of the intake air temperature sensor 36 are input to an ECU (Engine Control Unit) 100 incorporating a microcomputer.
[0020]
The exhaust pipe 41 is provided with three-way catalytic converters 42 and 43 for simultaneously purifying three harmful components HC, CO and NOx in the exhaust gas. The three-way catalytic converter 42 is activated early by electrical heating. It is a possible electrically heated catalyst (EHC), and the three-way catalytic converter 43 is a main catalyst activated by the exhaust temperature. An air-fuel ratio sensor 1 is provided in the exhaust pipe 41 on the upstream side of the EHC 42. The air-fuel ratio sensor 1 generates an electrical signal according to the oxygen component concentration in the exhaust gas. An exhaust temperature sensor 44 is provided in the exhaust pipe 41 near the downstream side of the main catalyst 43. The outputs of the air-fuel ratio sensor 1 and the exhaust temperature sensor are input to the ECU 100.
[0021]
Further, the ECU 100 has an accelerator pedal depression amount signal (accelerator opening amount signal) from an accelerator opening degree sensor 45 that is attached to an accelerator pedal (not shown) and detects an accelerator depression amount. From a rotational speed sensor 47 that detects the rotational speed of a ring gear (not shown) of the engine 30 to detect the key position signal (off position, on position, starter position) from the connected ignition switch 46 and the engine rotational speed NE. Each output pulse signal is input.
[0022]
Each means of the present invention, that is, the determination means, the energization limiting means, and the flow rate suppression means function by the configuration of the ECU 100.
The electrical control of the oxygen concentration detection device of the present invention will be described below. The present invention detects that moisture has adhered to the wall surface of the exhaust pipe in order to prevent element cracking of the air-fuel ratio sensor at the time of cold start of the engine as described with reference to FIG. The energization control of the heater 4 is performed so as to suppress or prohibit the energization to the heater 4.
[0023]
FIG. 4 is a flowchart of the heater control routine. The processing of this routine and the flowcharts shown in FIGS. 5, 6, 8, 9, and 10 are executed every predetermined processing cycle, for example, 64 ms. First, at step 401, it is determined whether the ignition switch (IGSW) 46 is on or off. When the IGSW 46 is on, the routine proceeds to step 402, and when the IGSW 46 is on, this routine is terminated.
[0024]
The processing of steps 402 to 414 will be briefly described. Electric power supply from the battery 5 to the heater 4 is started for early activation of the air-fuel ratio sensor 1, and electric power set in accordance with duty control at the start is supplied to the heater 4 until the heater temperature reaches a predetermined temperature ( When the heater temperature reaches a predetermined temperature, electric power corresponding to the heater temperature is supplied to the heater 4 (heater upper limit resistance F / B control). When the temperature of the air-fuel ratio sensor 1 reaches the predetermined temperature, the temperature is empty. Electric power for maintaining the sensor element 2 in an active state according to the element temperature of the fuel ratio sensor 1 is supplied to the heater 4 (element temperature F / B control). Next, the processing of steps 402 to 414 will be described individually.
[0025]
In step 402, the element DC impedance Zdc of the air-fuel ratio sensor 1 is calculated. The impedance Zdc is obtained by applying a negative voltage Vneg to the sensor element 2, detecting the current Ineg, and calculating Zdc = Vneg / Ineg. In general, there is a correlation that the element DC impedance decreases as the element temperature rises. For example, when the sensor element 2 has an activation temperature of 700 ° C., the element DC impedance is 30Ω.
[0026]
In step 403, it is determined whether or not the activation flag F1 of the air-fuel ratio sensor 1 is set. If F1 = 1, the process proceeds to step 404. In step 404, element temperature F / B control described later is executed, and F1 = When it is 0, the process proceeds to step 405.
In step 405, the temperature of the exhaust pipe is calculated. The exhaust pipe temperature calculation routine will be described later in detail with reference to FIG. In step 406, the exhaust pipe temperature T_EPIs the threshold T_thIt is determined whether or not it is greater than or equal to T_EP≧ T_thIn this case, it is determined that the water droplets adhering to the inner wall surface of the exhaust pipe have evaporated, and the routine proceeds to step 407, where the air-fuel ratio sensor 1 is heated early by steps 407 to 414, and T_EP<T_thIn this case, it is determined that moisture is attached to the inner wall surface of the exhaust pipe or that there is a high possibility that the moisture has adhered, that is, it is determined that the sensor element may be damaged by moisture, and this routine is terminated and empty. The early heating of the fuel ratio sensor 1 is not performed.
[0027]
In step 407, the activation determination of the sensor element 2 is performed based on the element DC impedance. That is, when Zdc> 30, it is determined that the sensor element 2 is activated, the activation flag F1 of the air-fuel ratio sensor 1 is set to 1 at step 308, and then element temperature F / B control is executed at step 404, and Zdc ≦ When it is 30, it is determined that the sensor element 2 is in an inactive state, and the process proceeds to step 409 to perform heater control for activating the sensor element 2. The flag F1 is reset by a one-shot pulse signal when the ignition switch IGSW 46 is switched from OFF to ON.
[0028]
In step 409, the voltage Vn and current In applied to the heater 4 are detected. In step 410, the resistance Rh of the heater 4 is calculated from Rh = Vn / In.
In step 411, it is determined whether or not the heater temperature has reached a heater upper limit temperature 1020 ° C lower than the heat-resistant limit temperature 1200 ° C of the heater 4 by a predetermined temperature. If the determination result is YES, the process proceeds to step 412. Then, the start-time DUTY control for supplying as much power as possible to the heater 4 is executed. When the determination result is NO, the process proceeds to step 413, and the heater 4 is controlled to maintain the heater upper limit temperature at 1020 ° C. Step 412 will be described in detail later using FIG. 6, and 413 will be described in detail later using FIG. Here, the reason why the upper limit temperature of the heater is not set to the heat resistant limit temperature of the heater 4 is that the resistance temperature characteristic of the heater 4 varies. When the median of the variation is used, the heater resistance Rh corresponding to the heater upper limit temperature of 1020 ° C. is 2.1Ω, and when the heater control is performed so that the heater resistance Rh is 2.1Ω, the heater temperature variation is 870 to 1200. It falls within the range of ° C and does not exceed the heat resistance limit temperature of the heater 4.
[0029]
In step 414, the voltage of the battery 5 is applied to the heater according to the DUTY ratio set in steps 412 and 413. Here, DUTY control means that when the cycle of turning on and off the voltage of the battery 5 to the heater 4 is 100 ms, for example, when the DUTY ratio is 20%, the on time is 20 ms, the off time is 80 ms, and the DUTY ratio is 50%. When the ON time is 50 ms, the OFF time is 50 ms, and the DUTY ratio is 100%, the control means that the voltage of the battery 5 is applied to the heater 4 in each cycle of the ON time of 100 ms. Next, step 405 of FIG. 4, that is, the exhaust pipe temperature calculation routine will be described below with reference to FIG.
[0030]
FIG. 5 is a flowchart of an exhaust pipe temperature calculation routine. In step 501, the outside air temperature T detected by the intake air temperature sensor 36._OARead. In step 502, the main catalyst detected by the exhaust temperature sensor 44.43Exhaust temperature T directly below_EA2 Read. In step 503, the outside air temperature T_OAAnd exhaust temperature T_EA2 And the exhaust temperature T in the vicinity of the air-fuel ratio sensor 1_EA1 Is estimated as follows.
[0031]
Outside temperature T_OAAnd the heat transfer coefficient k1 of the exhaust pipe, a decrease in exhaust temperature T from the vicinity of the air-fuel ratio sensor 1 to the vicinity of the exhaust temperature sensor 44 T_DGuess. Exhaust temperature T near the air-fuel ratio sensor 1_EA1Is the exhaust temperature T_EA2Exhaust temperature drop T_DSince the above is added, the following equation is established.
T_EA1= T_EA2+ T_D(1)
In step 504, the exhaust gas temperature T near the air-fuel ratio sensor 1 calculated in step 503 is calculated._EA1And the heat transfer coefficient k2 of the air to the exhaust pipe, the exhaust pipe temperature T around the air-fuel ratio sensor 1_EPIs calculated.
[0032]
Also, the exhaust pipe temperature T_EPMay be calculated as follows. First, the exhaust temperature T in the vicinity of the air-fuel ratio sensor 1_EA1Is calculated from a two-dimensional map of the engine speed NE detected from the engine speed sensor 47 and the intake air amount GA detected from an air flow meter (not shown). This two-dimensional map is created from experimental values. NE is greater, GA is greater, T_EA1Becomes higher. The exhaust temperature T calculated in this way_EA1And the outside air temperature T detected by the intake air temperature sensor 36_OAAnd exhaust pipe temperature T_EPIs calculated from the following equation.
[0033]
T_EP= Α (T_EA1-T_OA)
Where α is a constant. Next, step 412 of FIG. 4, that is, the start-time DUTY control will be described with reference to FIG.
FIG. 6 is a flowchart showing heater control at the time of engine start according to one embodiment, and FIG. 7 is a map for calculating element temperature from sensor element impedance. First, in step 601, the engine coolant temperature THW is read. In step 602, the element impedance of the air-fuel ratio sensor is detected. The element impedance may be detected in the same manner as in step 402 in FIG. 4, but here the element AC impedance is detected as follows.
[0034]
Usually, 0.3 (V), for example, is applied to the sensor element 2, and the limit current is detected at every predetermined period to calculate the exhaust air-fuel ratio. The AC impedance Zac applies a pulse voltage of 0.3 ± 0.2 (V) to the sensor element 2 every predetermined period, for example, every 64 ms, and detects the voltage Vac and current Iac of the sensor element 2 at that time. Calculate Zac = Vac / Iac. In general, there is a correlation that the element AC impedance is attenuated as the element temperature rises, similarly to the element DC impedance. In the case of detecting the element AC impedance, there is no need to apply a negative voltage to the sensor element 2 as in the case of detecting the element DC impedance, so that there is an advantage that the control circuit can be simplified.
[0035]
In step 603, the element temperature T of the air-fuel ratio sensor in the current processing cycle._iIs calculated from the sensor element impedance Zac detected in step 602 based on the map shown in FIG.
In step 604, it is determined whether or not the coolant temperature THW read in step 601 is less than 0 ° C. If THW <0 ° C, it is determined that the engine is cold, that is, moisture adheres to the inner wall surface of the exhaust pipe. The process proceeds to step 605, and when THW ≧ 0 ° C., the engine is warmed up and the sensor element 2 is wetted by evaporation of water adhering to the inner wall surface of the exhaust pipe. It is determined that there is not, and the process proceeds to Step 606.
[0036]
In step 605, the element temperature T calculated in the previous processing cycle is displayed._i-1To the element temperature T calculated in this processing cycle_iIs subtracted (ΔT = T_i-1-T_i). This ΔT indicates the degree of decrease per unit time of the element temperature of the air-fuel ratio sensor. In step 607, it is determined whether or not the subtraction value ΔT calculated in step 606 is greater than 5 ° C. If ΔT> 5 ° C, it is determined that the sensor element 2 has been submerged or its possibility is high. Proceeding to 608, if ΔT ≦ 5 ° C., it is determined that the sensor element 2 is not wet or its possibility is low, and the processing proceeds to step 606. In Step 608, when the subtraction value ΔT, that is, the degree of decrease in the element temperature of the air-fuel ratio sensor per unit time is larger than the reference value 5 ° C., the same electric power as the previous processing cycle is supplied to the heater 4, Since the element crack of the sensor element occurs due to the thermal shock caused by the water exposure, DUTY = 0 is set to prevent this. On the other hand, in step 606, since it is determined that the sensor element 2 is not wet, DUTY = 100 is set so as to supply all power to the heater 4 for early activation of the sensor element 2.
[0037]
Further, as described in steps 602 and 603 of FIG. 6, the element temperature of the air-fuel ratio sensor is calculated from the element impedance of the air-fuel ratio sensor. However, in the stacked air-fuel ratio sensor, the heater and the sensor element are close to each other. Alternatively, the element temperature of the air-fuel ratio sensor may be estimated by detecting the heater resistance and calculating the heater temperature from the heater resistance value.
[0038]
Note that although DUTY = 0 is set in step 608, in step 608, for example, DUTY = 20 may be set as a power supply that does not cause sensor element cracking for early activation of the sensor element 2.
Next, steps 609 to 614 will be described. Steps 609 to 614 set a time from when it is determined that the sensor element 2 has been submerged until the sensor element 2 returns to the normal start-up DUTY control. In step 609, it is determined whether or not the flag F3 indicating that the sensor element 2 has been determined to be wet is set. If F3 = 1, the process proceeds to step 610. If F3 = 0, the process proceeds to step 611. . In step 611, the flag F3 is set.
[0039]
In step 610, a counter C for measuring the time since F3 = 1 is set is counted up (C = C + 1). In step 612, it is determined whether or not 6400 ms, that is, 6.4 seconds has elapsed since F3 = 1 is set. If the determination result is YES, the process proceeds to step 613, and if the determination result is NO, this routine Exit. In step 613, F3 is reset (F3 = 0), and in step 614, the counter C is reset (C = 0).
[0040]
By the processing of the above steps 609 to 614, it is possible to return to the normal start-up DUTY control 6.4 seconds after it is determined that the sensor element 2 has been wetted, and every time the sensor element is wetted, it is determined to be 6.4. Energization of the heater 4 is prohibited for a second. Next, step 413 in FIG. 4, that is, the heater upper limit resistance F / B control will be described in detail with reference to FIG.
[0041]
FIG. 8 shows heater control based on the heater upper limit resistance. First, in step 801, it is determined whether or not the heater power control flag F2 indicating that the heater power control is being executed is set. If F2 = 1, the process proceeds to step 802. If F1 = 0, the process proceeds to step 803. In step 803, 20% is set as the initial duty ratio of the heater power control. This 20% is a value selected so that a sudden change in the heater temperature is suppressed when the heater voltage control is shifted to the power control. Next, at step 804, F2 is set. The flag F2 is reset by a one-shot pulse signal when the ignition switch IGSW is switched from OFF to ON.
[0042]
In step 802, it is determined whether or not the heater resistance Rh is greater than 2.5Ω in order to perform control for protecting the heater 4 from being abnormally heated due to an increase in the exhaust gas temperature accompanying a sudden change in engine operating conditions. When Rh> 2.5Ω, the process proceeds to step 805, and when Rh ≦ 2.5Ω, the process proceeds to step 806. In step 806, DUTY = DUTY-10 is calculated, and the calculated value is set to a new DUTY ratio. When DUTY becomes a negative value, DUTY = 0 is set.
[0043]
In step 805, the heater power Wh is calculated from the following equation.
Wh = Vn × In × DUTY / 100
Here, Vn and In indicate the voltage value and current value detected in step 807 of FIG. 4, and DUTY indicates the DUTY ratio set in step 803, 806, 808 or 809 in the previous processing cycle.
[0044]
In step 807, the heater power Wh in the current processing cycle is compared with the heater power supply 21W corresponding to the heat-resistant limit temperature 1200 ° C of the heater 4. When Wh ≦ 21, the power supplied to the heater 4 is lower than the target power. The process proceeds to step 808, and the duty ratio is increased by 3% (duty = duty + 3 is calculated) in step 808 to increase the power supplied to the heater 4. When Wh> 21, the power supplied to the heater 4 is the target. It is determined that the electric power is higher than the electric power, and the process proceeds to step 809. In step 809, the duty ratio is subtracted by 3% (DUTY = DUTY-3 is calculated) to reduce the electric power supplied to the heater 4.
[0045]
By controlling the heater based on the DUTY set as described above, the actual power supplied to the heater 4 can be controlled to the target power 21 (W).
Next, the element temperature F / B control in step 404 of FIG. 4 will be described. Based on the element DC impedance Zdc detected in step 402, the duty ratio of the voltage applied to the heater 4 is set based on the following equation so that the element DC impedance Zdc is 30 (Ω) corresponding to an element temperature of 700 ° C. Calculate.
[0046]
DUTY = GP + GI + c
GP = a (Zdc-30) ... proportional term
GI = GI + b (Zdc-30) ... integral term
Here, a, b, and c are constants of, for example, a = 4.2, b = 0.2, and c = 20. By controlling the heater 4 with the duty ratio calculated as described above, the element DC impedance Zdc can be controlled in the vicinity of 30 (Ω), the sensor element can always be maintained in a good active state, and damage to the sensor element due to abnormal heating can be prevented. it can.
[0047]
Next, before the engine is started by the ignition key, immediately after the driver opens and closes the door on the driver's seat and closes the door, the air-fuel ratio sensor 1 starts preheating control. An example applied to an engine without an electronic throttle will be described below with reference to FIG. 9, and an example applied to an engine with an electronic throttle will be described with reference to FIG.
[0048]
FIG. 9 is a flowchart of the preheat control routine of the air-fuel ratio sensor. First, in step 901, it is determined whether a courtesy switch (not shown), that is, a door switch on the driver's seat side is ON and the driver is seated in the driver's seat. If the determination result is YES, the process proceeds to step 902. When the determination result is NO, this routine is finished. In step 902, the voltage V of the battery 5_BWhether or not is 10V or more, and V_BWhen ≧ 10V, the process proceeds to step 903 and V_BWhen <10 V, this routine is terminated.
[0049]
In step 903, the exhaust temperature T calculated by executing the exhaust temperature calculation routine shown in FIG._EPDetermines whether or not the dew point has exceeded 60 ° C, T_EPWhen ≦ 60 ° C., it is determined that the sensor element may be damaged due to evaporation of water adhering to the inner wall surface of the exhaust pipe, and the process proceeds to step 904. In step 904, the element temperature of the air-fuel ratio sensor is reduced to about Execute first element temperature F / B control to control at 350 ° C, T_EPWhen it is> 60 ° C., it is determined that the water adhering to the inner wall surface of the exhaust pipe has evaporated and there is no possibility that the sensor element will be wetted and damaged, and the process proceeds to step 905. In step 905, the element temperature of the air-fuel ratio sensor The second element temperature F / B control for controlling the temperature to about 700 ° C. is executed. Here, the air-fuel ratio sensor 1 performs the λ-type O during the first element temperature F / B control.₂It is used for air-fuel ratio control as a sensor, and is used for wide-range air-fuel ratio control as a limiting current type oxygen concentration detection element while performing the second element temperature F / B control. In the first and second element temperature F / B control, the element DC impedance Zdc is calculated, and the same control as step 404 in FIG. 4 is executed.
[0050]
FIG. 10 is a flowchart of an air-fuel ratio sensor preheat control routine in an engine with an electronic throttle. First, in step 1001, it is determined whether a courtesy switch (not shown), that is, a door switch on the driver's seat side is turned on and the driver is seated in the driver's seat. If the determination result is YES, the process proceeds to step 1002. When the determination result is NO, this routine is finished. In step 1002, the voltage V of the battery 5_BWhether or not is 10V or more, and V_BWhen ≧ 10V, the process proceeds to step 1003 and V_BWhen <10 V, this routine is terminated.
[0051]
In step 1003, the exhaust temperature T calculated by executing the exhaust temperature calculation routine shown in FIG._EPDetermines whether or not the dew point has exceeded 60 ° C, T_EPWhen ≦ 60 ° C., it is determined that the sensor element may be damaged due to evaporation of water adhering to the inner wall surface of the exhaust pipe, and the process proceeds to Steps 1004 to 1006. In Step 1004, the element temperature of the air-fuel ratio sensor is determined. The first element temperature F / B control is performed to control T to about 380 ° C., and T_EPWhen it is> 60 ° C., it is determined that the water adhering to the inner wall surface of the exhaust pipe has evaporated and there is no possibility that the sensor element is wetted and damaged, and the process proceeds to Step 1007. The second element temperature F / B control for controlling the temperature to about 700 ° C. is executed.
[0052]
In step 1005, the throttle valve opening guard value θ_maxOn the basis of the map shown in FIG._EPSet according to. Next, in step 1006, ETC (Electronic Controlled Transmission), that is, from the first speed (Low) to the second speed (2nd) by the automatic transmission, from the second speed to the third speed (3rd), from the third speed to the fourth speed (4th). Based on the map shown in FIG. 12, the exhaust pipe temperature T is the vehicle speed during automatic gear shifting (hereinafter referred to as the gear shifting vehicle speed)._EPCorrect according to.
[0053]
Here, an example of a gear ratio control program by the automatic transmission will be briefly described. It is assumed that the throttle valve opening is accelerated from 0 ° to 50 °, accelerated, returned to 10 ° when the vehicle speed reaches 50 km / h, and then moved to steady running. During acceleration, the speed is changed from 2nd to 3rd when the throttle valve opening is returned by 10 ° from Low to 2nd. During this time, the engine speed increases as the acceleration time elapses, but decreases during a shift. If the vehicle speed when shifting from Low to 2nd is lowered, the time to reach 50 km / h becomes longer and the acceleration becomes worse, but the fuel consumption in the acceleration period of 0 to 50 km / h is improved.
FIG. 11 is a diagram showing a two-dimensional map of the exhaust pipe temperature and the throttle opening guard value. In FIG. 11, the horizontal axis represents the exhaust pipe temperature T._EP(° C), the vertical axis represents the guard value θ of the throttle valve opening_max(°). Until the temperature of the exhaust pipe reaches 60 ° C., it is determined that the sensor element may be damaged by moisture, and the guard value θ of the throttle valve opening is set to slow down the exhaust flow velocity._maxIs set to a value lower than normal of 30 ° to 90 °, the intake air amount of the engine is reduced, the engine speed is made lower than normal, and the exhaust flow rate is made slower. By slowing down the exhaust flow rate, scattering of water droplets adhering to the inner wall of the exhaust pipe is suppressed, and the sensor element is prevented from getting wet. On the other hand, when the temperature of the exhaust pipe reaches 60 ° C. or more, it is determined that the water droplets adhering to the inner wall of the exhaust pipe are evaporated, and the guard value θ of the throttle valve opening_maxIs set to a normal value of 90 °, and the control to slow down the exhaust gas flow rate is stopped.
[0054]
FIG. 12 is a diagram showing a two-dimensional map of the exhaust pipe temperature and the shift vehicle speed correction coefficient. In FIG. 11, the horizontal axis represents the exhaust pipe temperature T._EP(° C), and the vertical axis represents the shift vehicle speed correction coefficient k. Until the temperature of the exhaust pipe reaches 60 ° C, it is determined that the sensor element may be damaged by water, the transmission vehicle speed correction coefficient k is set to a value of 0.8 to 1.0, and the engine speed Is lower than usual, and the exhaust flow rate is decreased. By slowing down the exhaust flow rate, scattering of water droplets adhering to the inner wall of the exhaust pipe is suppressed, and the sensor element is prevented from getting wet. On the other hand, when the temperature of the exhaust pipe reaches 60 ° C. or more, it is determined that the water droplets adhering to the inner wall of the exhaust pipe have evaporated, the shift vehicle speed correction coefficient k is set to a value of 1.0, and the engine Set the engine speed to normal and stop the control to slow down the exhaust flow rate. Here, the shift vehicle speed correction coefficient k automatically shifts the vehicle speed from the first speed (Low) to the second speed (2nd), from the second speed to the third speed (3rd), from the third speed to the fourth speed (4th) by the automatic transmission. For example, the vehicle speed when switching from 2nd to 3rd is 30 km / h when k = 1.0, and 24 km / h when k = 0.8.
[0055]
【The invention's effect】
As described above, according to the oxygen concentration detection device of the present invention, when supplying power to the heater of the air-fuel ratio sensor during cold start of the engine or pre-heating of the air-fuel ratio sensor before starting, the element of the air-fuel ratio sensor Since the energization of the heater is limited when it is determined that moisture has adhered to the exhaust pipe wall surface, the energization to the heater is limited. It is possible to prevent element cracking of the air-fuel ratio sensor due to thermal shock caused by water.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of an oxygen concentration detection apparatus according to the present invention.
FIG. 2 is a cross-sectional view of a cup-type oxygen sensor.
FIG. 3 is a configuration diagram of an internal combustion engine equipped with the oxygen concentration detection device shown in FIG. 1;
FIG. 4 is a flowchart of a heater control routine.
FIG. 5 is a flowchart of an exhaust pipe temperature calculation routine.
FIG. 6 is a flowchart showing heater control at the time of engine start according to an embodiment.
FIG. 7 is a map for calculating element temperature from sensor element impedance.
FIG. 8 is a flowchart showing heater control based on a heater upper limit resistance.
FIG. 9 is a flowchart of a preheat control routine of the air-fuel ratio sensor.
FIG. 10 is a flowchart of a preheat control routine for an air-fuel ratio sensor in an engine with an electronic throttle.
FIG. 11 is a diagram showing a two-dimensional map of exhaust pipe temperature and throttle opening guard value.
FIG. 12 is a diagram showing a two-dimensional map of exhaust pipe temperature and shift vehicle speed correction coefficient.
[Explanation of symbols]
1. Air-fuel ratio (A / F) sensor
2 ... Sensor element
3. Air-fuel ratio (A / F) sensor circuit
4 ... Heater
5 ... Battery
6 ... Heater control circuit
7 ... LPF
10. Air-fuel ratio control unit (A / FCU)
27, 41 ... exhaust pipe
30 ... Institution
33 ... Throttle valve
34 ... Throttle motor
35 ... Throttle opening sensor
36 ... Intake air temperature sensor
38 ... Fuel injection valve
42, 43 ... Three-way catalytic converter
44 ... Exhaust temperature sensor
100: Electronic control unit (ECU)

Claims (2)

An oxygen provided with an air-fuel ratio sensor provided in an exhaust pipe of an internal combustion engine, a heater for heating the air-fuel ratio sensor, and heater energizing means for energizing the heater so that the air-fuel ratio sensor becomes an activation temperature In the concentration detector,
Means for detecting the outside air temperature flowing into the intake pipe of the internal combustion engine;
First calculation means for calculating a first exhaust temperature downstream of the catalyst provided downstream of the air-fuel ratio sensor in the exhaust pipe of the internal combustion engine;
Second calculating means for calculating a second exhaust temperature around the air-fuel ratio sensor based on the outside air temperature and the first exhaust temperature;
Exhaust pipe temperature calculating means for calculating the temperature of the exhaust pipe around the air-fuel ratio sensor from the second exhaust temperature and the heat transfer coefficient of the exhaust pipe;
Determining means for determining whether moisture has adhered to the wall surface of the exhaust pipe based on the temperature of the exhaust pipe calculated by the exhaust pipe temperature calculating means ;
Energization limiting means for limiting energization to the heater by the heater energizing means when the determining means determines that moisture is attached to the wall surface of the exhaust pipe;
An oxygen concentration detection apparatus comprising: A flow rate suppressing means for suppressing the flow rate of the exhaust gas of the internal combustion engine when the determining means determines that moisture is attached to the wall surface of the exhaust pipe;
The oxygen concentration detection apparatus according to claim 1.

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