JPH0933480A - Oxygen sensor and air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oxygen sensor and an air-fuel ratio controller having simple structure which can be operated effectively for a long term. SOLUTION: The oxygen sensor 10 comprises an oxygen ion conductive solid electrolyte part 12, electrode parts provided on the inner and outer surfaces thereof, and a heater part 14 provided in the electrolyte part 12. The heater part 14 comprises a plurality of heater element patterns 18a-18c being connected in parallel with a power supply and driven selectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor and an air-fuel ratio control system for an internal combustion engine incorporating the oxygen sensor.

[0002]

2. Description of the Related Art For example, a concentration sensor for detecting an exhaust gas concentration is provided in an exhaust system of an internal combustion engine such as an engine, and the air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine is determined based on the output value of the concentration sensor. There is known a technique for reducing harmful exhaust gas components discharged from the internal combustion engine by performing feedback control. As this type of concentration sensor, an oxygen sensor with a built-in electric resistance heating element is generally used.

FIG. 7 shows a main part of an oxygen sensor disclosed in Japanese Patent Laid-Open No. 4-157358, and a rod-shaped ceramic heater is provided inside a solid electrolyte part 1 made of an oxygen ion conductive metal oxide. 2 is inserted. The ceramic heater 2 includes a ceramic rod 3 made of alumina.
And a comb-shaped heating element 4 provided on the surface of the ceramic rod 3 on the tip end side.

According to this oxygen sensor, the solid electrolyte portion 1
It is stated that when the vicinity of the tip end of the oxygen sensor is heated by the heating element 4, the oxygen sensor can be rapidly started up, and the sensor activation time can be shortened.

[0005]

However, in the above-mentioned prior art, when the combustion products such as oil and additives contained in the exhaust gas adhere to the tip side of the solid electrolyte part 1, the solid electrolyte part 1 deteriorates. As a result, it becomes impossible to supplement the function of the oxygen sensor even with the heating element 4. This is because the combustion products do not adhere to the solid electrolyte part 1 made of zirconia or the like and electromotive force is not generated, and as a result, the life of the oxygen sensor is significantly reduced.

The present invention solves this type of problem, and an object of the present invention is to provide an oxygen sensor and an air-fuel ratio control device for an internal combustion engine that can be effectively used for a long period of time with a simple structure. .

[0007]

In order to achieve the above objects, the present invention provides an oxygen ion conductive solid electrolyte part,
An oxygen sensor comprising: an electrode part provided on the inner and outer surfaces of the solid electrolyte part; and a heater part provided inside the solid electrolyte part, wherein the heater part is connected in parallel to a power source. It has a plurality of heating element patterns.

Therefore, if a plurality of heating element patterns are selectively connected to the power source, each part of the solid electrolyte portion corresponding to each heating element pattern can be effectively functioned, and the whole solid electrolyte portion can be effectively operated. The oxygen sensor is effectively utilized to improve the life of the oxygen sensor.

Further, according to the present invention, there is provided an oxygen sensor arranged in an exhaust system of an internal combustion engine for detecting an exhaust gas concentration of the internal combustion engine, and a deterioration detecting means for detecting a deterioration state of the oxygen sensor. In the air-fuel ratio control device for an internal combustion engine, the oxygen sensor is an oxygen ion conductive solid electrolyte portion, an electrode portion provided on the inner and outer surfaces of the solid electrolyte portion, and the inside of the solid electrolyte portion. And a heater unit provided in the heater unit, the heater unit switching between the plurality of heating element patterns connected in parallel to the power source and the plurality of heating element patterns according to the deterioration state of the oxygen sensor. And a switching means.

Therefore, when the deterioration state of the oxygen sensor is detected by the deterioration detecting means, the heating element pattern corresponding to the portion where deterioration has progressed is switched to the heating element pattern corresponding to the portion where deterioration has not progressed. This effectively improves the functional life of the oxygen sensor. Therefore, it becomes possible to effectively use the air-fuel ratio control device for a long period of time.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In FIG.
1 shows an oxygen sensor according to an embodiment of the present invention. The oxygen sensor 10 includes an oxygen ion conductive solid electrolyte portion 12 and
An electrode portion (not shown) provided on the inner and outer surfaces of the solid electrolyte portion 12 and a heater portion 14 provided inside the solid electrolyte portion 12 are provided.

The solid electrolyte portion 12 has a substantially cylindrical shape with its tip closed, and, for example, zirconia is used as an oxygen ion conductive metal oxide. The electrode portion is made of platinum or a white metal alloy, and the solid electrolyte portion 12
It is provided on the inner and outer surfaces of. The heater portion 14 is a rod-shaped ceramic insulator 16 inserted into the solid electrolyte portion 12.
And a plurality of heating element patterns 18a to 18c arranged along the axial direction of the ceramic insulator 16.

In the heater section 14, heating element patterns 18a to 18c made of a refractory metal material such as tungsten (W) or molybdenum (Mo) are embedded in a ceramic insulator 16 containing alumina or mullite as a main component. The manufacturing method is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-31505.
No. 5 is disclosed.

As shown in FIG. 2, the first heating element pattern 1
8a is provided on the tip edge portion of the ceramic insulator 16 in a comb tooth shape. The second heating element pattern 18b and the third heating element pattern 18 are separated from the first heating element pattern 18a by a predetermined distance to the rear side of the ceramic insulator 16.
c is provided.

As shown in FIG. 3, the first heating element pattern 1
The first terminal wires 20a and 22a are connected to both ends of 8a, and the second terminal wires 20b and 22b and the third terminal wires 20c and 22c are connected to both ends of the second and third heating element patterns 18b and 18c, respectively. Has been done. First terminal wire 20a-
The third terminal wire 20c extends in the axial direction of the ceramic insulator 16, and each end of the third terminal wire 20c is connected in parallel to a power supply 26 via a changeover switch (switching means) 24. First
Similarly, the terminal wire 22a to the third terminal wire 22c extend in the axial direction of the ceramic insulator 16 and their ends are integrally grounded.

Next, the oxygen sensor 1 configured as described above.
An air-fuel ratio control device 30 incorporating 0 will be described with reference to FIG. As the air-fuel ratio control device 30, the configuration disclosed in Japanese Patent Application No. 6-73914 by the present applicant is adopted.

The air-fuel ratio control device 30 includes, for example, a four-cylinder internal combustion engine (hereinafter, referred to as engine) 32, and a throttle body 36 is provided in the intake pipe 34 of the engine 32.
Is provided. A throttle valve 38 is provided inside the throttle body 36, and a throttle valve opening (θTH) sensor 40 is connected to the throttle valve 38, and an electric signal corresponding to the opening of the throttle valve 38 is output to output an electronic signal. It is supplied to a control unit (hereinafter referred to as ECU) 42.

The fuel injection valve 43 is provided for each cylinder in the middle of the intake pipe 34 and slightly upstream of an intake valve (not shown) provided between the engine 32 and the throttle valve 38. Each fuel injection valve 43 is connected to a fuel pump (not shown) and electrically connected to the ECU 42.
The valve opening timing of fuel injection is controlled by the signal from U42.

A purge pipe 44 is branched and provided on the intake pipe 34 on the downstream side of the throttle valve 38, and the purge pipe 44 is connected to an evaporative fuel discharge inhibiting system (not shown). Intake pipe 3
4, a branch pipe 46 is provided on the downstream side of the purge pipe 44, and an absolute pressure (PBA) sensor 48 is provided at the tip of the branch pipe 46. The PBA sensor 48 is electrically connected to the ECU 42, and the absolute pressure PBA in the intake pipe 34 detected by the PBA sensor 48 is converted into an electric signal to be converted into the E signal.
It is supplied to the CU 42. An intake air temperature (TA) sensor 50 is mounted on the intake pipe 34 downstream of the branch pipe 46, and the intake air temperature TA detected by the TA sensor 50 is converted into an electric signal and supplied to the ECU 42. .

In the engine 32, an engine water temperature (TW) sensor 52 composed of a thermistor or the like is attached to the cylinder peripheral wall filled with the cooling water of the cylinder block.
The engine water temperature TW detected by the sensor 52 is converted into an electric signal and supplied to the ECU 42. Engine 32
An engine speed (NE) sensor 54 is attached around a cam shaft or a crank shaft (not shown). N
The E sensor 54 has a crankshaft of the engine 32 of 180 °.
A signal pulse (hereinafter referred to as a TDC signal pulse) is output at a predetermined crank angle position each time it rotates, and this TDC signal pulse is supplied to the ECU 42.

The transmission 56 is interposed between a wheel (not shown) and the engine 32, and the vehicle speed (V
SP) sensor 58 is attached to the VSP sensor 58
The vehicle speed VSP detected by is converted into an electric signal and E
It is supplied to the CU 42.

Spark plug 60 for each cylinder of engine 32
Is electrically connected to the ECU 42, and the ignition timing is controlled by the ECU 42. A catalyst device (three-way catalyst) 64 is interposed in the exhaust pipe 62 of the engine 32, and the catalyst device 64 purifies harmful components such as HC, CO, and NOx in the exhaust gas.

An oxygen sensor 10 is provided in the exhaust pipe 62 and upstream of the catalyst device 64.
The oxygen concentration in the exhaust gas detected by 0 is converted into an electric signal and supplied to the ECU 42. Oxygen sensor 10
As described above, the sensor element is made of zirconia solid electrolyte (ZrO ₂ ), and the electromotive force of the sensor element changes rapidly before and after the stoichiometric air-fuel ratio. Inverts the rich signal or the rich signal to the lean signal. That is, the output signal of the oxygen sensor 10 has a high level on the rich side of the air-fuel ratio and has a low level on the lean side, and the output signal is supplied to the ECU 42.

On the output side of the ECU 42, a light emitting diode (L
A warning light 66 such as ED) is connected. The warning light 66 is provided, for example, on a dashboard in the passenger compartment of an automobile to inform the driver of deterioration of the oxygen sensor 10 based on an output signal from the ECU 42.

The ECU 42 shapes the input signal waveforms from the various sensors described above, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like, and a central processing unit. Processing circuit (hereinafter,
A CPU 70, a storage unit 72 for storing a calculation program executed by the CPU 70, a calculation result, and the like, and an output circuit 74 for supplying a drive signal to the fuel injection valve 43 and the ignition plug 60.

The CPU 70 discriminates various engine operating states such as a feedback control operating region and an open loop control operating region according to the oxygen concentration in the exhaust gas based on the various engine parameter signals described above, and at the same time, the engine operating state. in response, (1) based on the formula, the fuel injection time T _{ou t} of the fuel injection valve 43 synchronized with the TDC signal pulse
Is calculated.

T _out = Ti × K ₀₂ × K ₁ + K ₂ (1) Here, Ti is determined according to the basic fuel injection time, specifically, the engine speed NE and the intake pipe absolute pressure PBA. The Ti map for determining the Ti value is stored in the storage unit 72.

K ₀₂ is an air-fuel ratio correction coefficient calculated based on the oxygen sensor 10, and the air-fuel ratio detected by the oxygen sensor 10 (during the air-fuel ratio feedback control by executing the calculation routine of K ₀₂ described later). The oxygen concentration) is set to match the target air-fuel ratio, and is set to a predetermined value according to the operating state of the engine 32 during open loop control.

K ₁ and K ₂ are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, and fuel consumption characteristics according to the engine operating state,
It is set to a value that optimizes various characteristics such as engine acceleration characteristics.

Next, regarding the operation of the oxygen sensor 10,
It will be described below in connection with the air-fuel ratio control device 30 incorporating this.

First, as shown in FIG. 3, the changeover switch 2
The power source 26 is connected to the first heating element pattern 18a from the first terminal line 20a via the first terminal wire 20a, and the first element portion 1 of the solid electrolyte portion 12 corresponding to the first heating element pattern 18a.
2a (see FIG. 1) detects the exhaust gas concentration of the engine 32.

FIG. 5 is a deterioration detecting routine for detecting deterioration of the oxygen sensor 10. This program is executed by the ECU 4
It is executed every 100 msec, for example, by a signal pulse generated by a timer built in 2.

In step S1, programming F _MON
Is set to "1". If the result of this determination is negative (NO), the monitoring condition is not satisfied, and this program ends. On the other hand, when the determination result of step S1 is affirmative (YES), it is determined whether the flag F _K02LMT is “1”, and the air-fuel ratio correction coefficient K ₀₂ is attached to the predetermined upper limit value or the predetermined lower limit value. Or not, that is, whether or not K ₀₂ is set to the predetermined upper limit value or the predetermined lower limit value (step S2).

Then, the determination result is affirmative (YES),
That is, when the K ₀₂ value is attached to the predetermined upper limit value or the predetermined lower limit value, the process proceeds to step S3 and the flag F
_DONE is set to "1" and this program ends. That is, the flag F _DONE is a flag that is set to “0” when instructing to start the deterioration detection of the oxygen sensor 10, and as a result, is set to “1” when the detection has been executed, and the air-fuel ratio correction coefficient. When K ₀₂ is attached to the upper limit value or the lower limit value, the flag F _DONE is set to "1", it is determined that the deterioration detection of the oxygen sensor 10 has already been executed, and this program ends.

On the other hand, when the flag F _K02LMT is not set to "1", the process proceeds to step S4, and it is determined whether or not the flag F _AF2 has been inverted from "0" at the previous time to "1" at this time.
Here, the flag F _AF2 is set to “0” when the air-fuel ratio of the air-fuel mixture is in the lean state, and is set to “1” after a predetermined time has elapsed since the air-fuel ratio of the air-fuel mixture was switched to the rich state. .

Therefore, when the determination result of step S4 is negative (NO), this program is ended as it is, and the determination result is affirmative (YES), that is, the air-fuel ratio of the air-fuel mixture is changed from lean to rich in this loop. If it is switched to step S5, it is determined whether or not the current reversal of the flag F _AF2 is the first reversal after the deterioration detection monitor of the oxygen sensor 10 is permitted. At that time, in the first loop, the determination result is affirmative (YES),
In step S6, the inversion number n _WAVE is set to "0" and the flag F _DONE is set to "0" (step S7), the start of the deterioration detection monitor is instructed, and the program ends.

When the determination result of step S5 becomes negative (NO) in the subsequent loop, the process proceeds to step S8, where the number of inversions n _WAVE is incremented by "1",
Then reversal number n _WAVE the counting time t _WAVE predetermined time T ₂
It is determined whether (for example, 10 seconds) has been exceeded (step S9). When the determination result is negative (NO), the program is terminated as it is, while when the determination result is affirmative (YES), the process proceeds to step S10, and the inversion cycle t _CYCL is calculated based on the equation (2).

T _CYCL = t _WAVE / n _WAVE (2) After the inversion period t _CYCL is calculated in this way, deterioration determination processing is executed (step S11), and the flag F _{DONE is set} to “1”.
To indicate the end of the deterioration detection monitor (step S
12) The program ends.

The deterioration determining process is specifically performed by executing a deterioration determining process routine shown in FIG.

That is, in step S21, the inversion cycle t _CYCL calculated in step S10 (FIG. 5) is the first.
It is determined whether or not it is shorter than the predetermined inversion cycle t _CY0 . Here, the first predetermined inversion period t _CY0 is an inversion period sufficient to determine that the oxygen sensor 10 has not deteriorated, for example,
It is set to 2 sec. When the determination result of step S21 is affirmative (YES), it is determined that the oxygen sensor 10 is normal (step S22), and the process returns to the main routine (FIG. 5).

On the other hand, if the answer to the question of the step S21 is negative (NO), the inversion cycle t _CYCL is, the second inversion period t _CY1 which is set longer than the first predetermined inversion period t _CY0,
That is, it is determined whether or not it is shorter than the second inversion cycle t _{CY1 having} the relationship of t _CY0 <t _CY1 . If the determination result is affirmative (YES), the oxygen sensor 10 is in a deteriorated state, but it is determined that the degree of deterioration is small enough not to prohibit feedback control (step S24), and the process returns to the main routine (FIG. 5). .

When the determination result of step S23 is negative (NO), it is determined that the oxygen sensor 10 is in a deteriorated state that causes deterioration of exhaust gas purification efficiency and drivability, and the deterioration degree is large (step S25) and returns to the main routine (FIG. 5).

As described above, when it is determined that combustion products such as oil and additives adhere to the first element portion 12a of the solid electrolyte portion 12 to cause deterioration such as clogging, FIG. The changeover switch 24 is driven, and the power supply 26 is connected to the second heating element pattern 18b via the second terminal line 20b. As a result, the main function part of the solid electrolyte part 12 is the first
From the element portion 12a to the second element portion 12b,
The element portion 12b detects the concentration of exhaust gas discharged from the engine 32.

Further, when the deterioration of the second element portion 12b is detected based on the above-described deterioration detecting routine, the power source 26 causes the third heating element pattern 18c via the changeover switch 24.
Connected to. Therefore, the main functional portion of the solid electrolyte portion 12 is transferred from the second element portion 12b to the third element portion 12c.

As described above, in the oxygen sensor 10, the first heating element pattern 18a, the second heating element pattern 18b and the third heating element pattern 18c constituting the heater section 14 are sequentially connected to the power source 26 via the changeover switch 24. By doing so, the entire axial direction of the solid electrolyte part 12 can be gradually switched to the main function part, and the functional life of the oxygen sensor 10 can be dramatically improved. As a result, C contained in the exhaust gas
It is possible to obtain the air-fuel ratio control device 30 that can effectively reduce the emissions of O, HC, NOx, etc. and can reliably control the emission for a long period of time.

[0046]

According to the oxygen sensor of the present invention, the heater portion has a plurality of heating element patterns, and by selectively connecting each heating element pattern to the power source, the entire solid electrolyte portion can be covered. The oxygen sensor can be utilized stepwise and effectively, and the functional life of the oxygen sensor is improved all at once.

Further, in the air-fuel ratio control system for an internal combustion engine according to the present invention, when the deterioration state of the oxygen sensor is detected by the deterioration detecting means, a new heating element pattern is connected to the power source, This allows the oxygen sensor to function automatically and reliably for a long period of time. This makes it possible to provide an air-fuel ratio control device having a long life.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional explanatory view of an oxygen sensor according to the present invention.

FIG. 2 is a perspective explanatory view of a tip portion of the oxygen sensor.

FIG. 3 is an explanatory diagram of electric wiring of the oxygen sensor.

FIG. 4 is a schematic configuration diagram of an air-fuel ratio control device incorporating the oxygen sensor.

FIG. 5 is a flowchart for detecting deterioration of the oxygen sensor.

FIG. 6 is a flowchart of a deterioration determination process of the oxygen sensor.

FIG. 7 is a schematic explanatory view of a conventional oxygen sensor.

[Explanation of symbols]

10 ... Oxygen sensor 12 ... Solid electrolyte part 14 ... Heater part 16 ... Ceramic insulator 18a-18c ... Heating element pattern 24 ... Changeover switch 26 ... Power supply 30 ... Air-fuel ratio control device 32 ... Engine 42 ... ECU 70 ... CPU

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Minoru Nakamura 1-10-1 Shin-Sayama, Sayama City, Saitama Prefecture Honda Motor Co., Ltd. Saitama Factory

Claims (2)

[Claims] 1. An oxygen sensor comprising: a solid electrolyte part having oxygen ion conductivity; an electrode part provided on inner and outer surfaces of the solid electrolyte part; and a heater part provided inside the solid electrolyte part. The heater section has a plurality of heating element patterns connected in parallel to a power source. 2. An internal combustion engine comprising: an oxygen sensor arranged in an exhaust system of an internal combustion engine for detecting an exhaust gas concentration of the internal combustion engine; and a deterioration detecting means for detecting a deterioration state of the oxygen sensor. An air-fuel ratio control device for an engine, wherein the oxygen sensor is provided with an oxygen ion conductive solid electrolyte part, an electrode part provided on inner and outer surfaces of the solid electrolyte part, and provided inside the solid electrolyte part. A heater section, wherein the heater section has a plurality of heating element patterns connected in parallel to a power source, and switching means for switching the plurality of heating element patterns in accordance with the deterioration state of the oxygen sensor, An air-fuel ratio control device for an internal combustion engine, comprising: