JPH0627721B2 - Control method of oxygen concentration sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for controlling an oxygen concentration sensor for detecting the oxygen concentration in exhaust gas of an internal combustion engine.

BACKGROUND ART The oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor in order to purify the exhaust gas of an internal combustion engine, improve fuel efficiency, etc., and the air-fuel ratio of the air-fuel mixture supplied to the engine is fed back to the target air-fuel ratio according to the detection level There is an air-fuel ratio control device to control.

As an oxygen concentration sensor used in such an air-fuel ratio control device, there is one that generates an output proportional to the oxygen concentration in the exhaust gas in a region where the air-fuel ratio of the air-fuel mixture supplied to the engine is higher than the theoretical air-fuel ratio ( Kaisho 58-15315
No. 5). In such an oxygen concentration sensor, an oxygen concentration detector having a pair of flat plate-shaped oxygen ion conductive solid electrolyte members is provided. The solid electrolyte member is arranged in exhaust gas, electrodes are respectively formed on the front and back surfaces of the solid electrolyte member, and the solid electrolyte members are arranged in parallel so as to face each other with a predetermined gap. ing. One of the solid electrolyte members acts as an oxygen pump element and the other acts as an oxygen concentration ratio measuring battery element. When a current is supplied between the electrodes of the oxygen pump element in the exhaust gas so that the gap side electrode becomes the negative electrode,
On the negative electrode surface side of the oxygen pump element, the oxygen gas in the gas in the gap is ionized, moves inside the oxygen pump element to the positive electrode surface side, and is discharged as oxygen gas from the positive electrode surface. At this time, a decrease in oxygen gas in the gap causes a difference in oxygen concentration between the gas in the gap and the gas outside the battery element. Therefore, if the supply current to the oxygen pump element, that is, the pump current is a constant value, A voltage proportional to the oxygen concentration difference between the electrodes of the element, that is, the oxygen concentration in the exhaust gas is generated. Based on the generated voltage of the battery element, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine is richer or leaner than the target air-fuel ratio. When the air-fuel ratio is controlled by the secondary air, if the air-fuel ratio is determined to be rich, the secondary air is supplied to the engine, and if the air-fuel ratio is determined to be lean, the air-fuel ratio is stopped by stopping the supply of the secondary air. The air-fuel ratio is controlled. If the pump current value supplied to the oxygen pump element is changed so that the generated voltage of the battery element is constant, the pump current value at constant temperature becomes almost proportional to the oxygen concentration in the exhaust gas. It is also possible to determine the air-fuel ratio from.

In such an oxygen concentration sensor, in order to obtain an output characteristic proportional to the oxygen concentration, it is necessary to make the temperature sufficiently higher than the exhaust gas temperature during steady operation (for example, 650 ° C. or higher). Therefore, a heating element composed of a heater is provided to heat the oxygen pump element and the battery element, and when measuring the oxygen concentration, a current is supplied to the heating element to cause the heating element to generate heat. However, when the engine is under high load, the amount of air-fuel mixture sucked into the engine increases and the combustion temperature rises.As a result, the exhaust gas temperature rises and becomes higher than the heat generation temperature of the heating element, and the heating element burns out. Or, it is a cause of rapid deterioration. Therefore, in order to protect the heating element, the present applicant has proposed a control method of stopping the current supply to the heating element at the time of high engine load. When this high load region is discriminated by the engine speed, when operating at around the reference speed for the high load discrimination, the current supply / stop of the current to the heating element is repeated, so the heating temperature of the heating element changes and the The output level of the oxygen concentration sensor fluctuates even if the fuel ratio is the same. Therefore, although the reference rotation speed can be set low, there is a problem that the feedback control region of the air-fuel ratio becomes narrow and the exhaust gas purification performance deteriorates. Further, if the current supply to the heating element is once stopped, it takes time until the oxygen pump element and the battery element are reactivated after the current supply to the heating element is restarted. Therefore, even if the engine speed becomes equal to or lower than the reference speed and the air-fuel ratio feedback control condition is satisfied, it is not possible to immediately determine the air-fuel ratio accurately from the output level of the oxygen concentration sensor. That is, the feedback control region of the air-fuel ratio is narrowed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a control method of an oxygen concentration sensor capable of protecting a heating element under high engine load while improving exhaust purification performance.

The control method of the oxygen concentration sensor of the present invention includes an oxygen concentration detecting element which is provided in an exhaust gas passage of an internal combustion engine and generates an output according to the oxygen concentration in the exhaust gas, and generates heat when a current is supplied from a power source. A method for controlling an oxygen concentration sensor having a heating element for heating an oxygen concentration detecting element by means of a heating element for detecting an engine operating parameter of an internal combustion engine and detecting a value of the engine operating parameter in a first region. Current supply is stopped, and when the detected value of the engine operating parameter is in the second region smaller than the first region, current is supplied to the heating element until the operating state continues for a predetermined time Stopping the current supply to the heating element and continuing the current supply to the heating element when the detected value of the engine operating parameter is in a region smaller than the first and second regions. It is characterized.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an air-fuel ratio control device for an on-vehicle internal combustion engine to which an oxygen concentration sensor control method according to the present invention is applied.
Intake manifold 23 downstream of throttle valve 22 of engine 21
An intake secondary air supply passage 25 connects the air cleaner 24 and the vicinity of the air outlet of the air cleaner 24. An electromagnetic opening / closing valve 26 is provided in the intake secondary air supply passage 25. The electromagnetic opening / closing valve 26 is designed to open by energizing the solenoid 26a.

On the other hand, 27 is an absolute pressure sensor which is provided in the intake manifold 23 and generates an output of a level according to the absolute pressure in the intake manifold 23, and 28 is an output of a level according to the rotation of a crankshaft (not shown) of the engine 21. A rotational speed sensor 29 for generating a cooling water temperature sensor, a cooling water temperature sensor 29 for generating an output level corresponding to the cooling water temperature of the engine 21, and a suction sensor 37 provided near the air intake port 20 for generating an output level corresponding to the intake air temperature. An air temperature sensor 30 is an oxygen concentration sensor that is provided in the exhaust manifold 31 of the engine 21 and generates an output proportional to the oxygen concentration in the exhaust gas. The electromagnetic opening / closing valve 26, the absolute pressure sensor 27, the rotation speed sensor 28, the water temperature sensor 29, and the intake air temperature sensor are connected to an air-fuel ratio control circuit 32 including a microcomputer. The air-fuel ratio control circuit 32 is further connected to an atmospheric pressure sensor 33 and an ignition switch 34, which generate an output of a level according to the atmospheric pressure. When the ignition switch 34 is turned on, the output voltage of a battery (not shown) mounted on the vehicle is supplied to the air-fuel ratio control circuit 32.

The oxygen concentration sensor includes a pump current supply circuit 35 that supplies a pump current to the oxygen pump element and a heater current supply circuit 36 that supplies a heater current to the heating element. The pump current supply circuit 35 and the heater current supply circuit 36 are also connected to the air-fuel ratio control circuit 32.

As shown in FIG. 2, the oxygen concentration sensor 30 has a housing 2 having a lead wire outlet 1 at one end,
An oxygen concentration detecting element 3 is attached to the other end of the housing 2. The oxygen concentration detection element 3 is surrounded by a cylindrical protection member 17, and is fitted to the tip of the housing 2 at one end of the protection member 17. For example, four exhaust gas passage holes 17a are formed in the protective member 17 at equal intervals in the circumferential direction. The portion on the left side of the line AA in the figure is located inside the exhaust manifold 31.

As shown in FIG. 3, the oxygen concentration detection element 3 has a pair of longitudinal flat plate-shaped elements 4 and 5 which are parallel to each other, and plate-shaped heating elements 6 and 7 are attached to both sides thereof. As is clear from FIGS. 4 and 5, the elements 4 and 5 are arranged in parallel so that their principal surfaces face each other, and a gap 8 is provided between one end in each longitudinal direction and the other end is provided. Are connected via a spacer 9. One element 4 is an oxygen pump element, the main body of which is a sintered body of oxygen ion conductive solid electrolyte. At one end 4a of the oxygen pump element 4, square electrode layers 11 and 12 made of a porous heat-resistant metal are provided at opposite positions on the front and back surfaces thereof, respectively. A lead wire 11a made of a heat-resistant metal and linearly extending to the other end 4b of the element 4 is connected to one electrode layer 11.
The lead wire 11a is connected to a corner of the square electrode layer 11. Similarly, the lead wire 1 that reaches the other end portion 4b of the oxygen pump element 4 linearly on the other electrode layer 12 as well.
2a is connected. However, this lead wire 12a
Is the lead line 1 among the corners of the square electrode layer 12.
1a is connected to the corner of the electrode layer 11 which is not connected to the corner. The lead wire 12a is the other end 4 of the element 4.
a through hole 4 penetrating the front and back of the element 4 in FIG.
It is connected to the take-out portion 12b on the opposite side through c. The lead wire 11a is connected to the lead-out portion 11b formed on the other end 4b. That is, the lead-out portions 11 of the electrode layers 11 and 12 are formed on one main surface of the element 4.
b and 12b are arranged.

The other element 5 is a battery element for measuring an oxygen concentration ratio, and its main body is a sintered body of an oxygen ion conductive solid electrolyte, like the oxygen pump element 4. This battery element 5 has the same structure as the oxygen pump element 4, and has square electrode layers 13 and 14 and lead lines (13a) and 14 on its front and back surfaces.
The lead-out portions (13b) and 14b are formed on the main surface of the electrode layer 13 having a. The lead wire 14a and the take-out portion 14b are connected through a through hole 5c.

A typical material used as the oxygen ion conductive solid electrolyte which is the main component of the elements 4 and 5 described above is a solid solution such as yttria or calcia of zirconia.
Solid solutions such as cerium dioxide, thorium dioxide and hafnium dioxide can be used. Further, the electrode layers 11 to 14, the lead lines 11a to 14a, the take-out portion 11
As b to 14b, Pt, Ru, Pd or the like is used, and specifically, these metals are deposited by flame spraying, chemical plating or vapor deposition.

Here, the plate-shaped heating elements 6 and 7 shown in FIG. 3 will be described.

The heating elements 6 and 7 are mainly composed of an insulating inorganic plate-like body such as a rectangular alumina or spinel whose longitudinal dimension is slightly smaller than that of the elements 4 and 5. At one end of the heating element 6, an opening 6a adapted to the position and shape of the electrode layer 11 on the element 4 is formed. A heater wire 6b is arranged in a wavy pattern around the opening 6a in the heating element 6, and is electrically connected to a lead-out portion 6c formed at the other end of the heating element 6 through a lead wire 6d. ing. In addition,
The heater wire 6b, the take-out portion 6c, and the lead wire 6d are P
It is made of a heat-resistant metal such as t. Also, although not shown,
The other heating element 7 is also provided with the same openings, heater wires (7b), etc. as the heating element 6.

Next, an oxygen concentration detection situation by the oxygen concentration sensor 30 having the above configuration will be described.

A pump current is supplied between the electrode layers 11 and 12 by the pump current supply circuit 35 so that the outer electrode layer 11 of the oxygen pump element 4 becomes a positive electrode, so that oxygen ions inside the solid electrolyte of the oxygen pump element 4 become the inner electrode. Oxygen existing in the gap 8 between the oxygen pump element 4 and the battery element 5 moves from the layer 12 to the outer electrode layer 11 and is pumped to the outside of the oxygen pump element 4.

When oxygen is pumped out from the gap portion 8 as described above, an oxygen concentration difference is generated outside the battery element 5, that is, between the exhaust gas and the gas inside the gap portion 8. Due to this oxygen concentration difference, a voltage is generated between the electrode layers 13 and 14 of the battery element 5. This voltage is reached when the amount of oxygen that freely flows into the oxygen concentration sensor 30 through the three-direction openings of the gap 8 and the amount of oxygen pumped out of the gap 8 by the oxygen pump element 4 reach an equilibrium state. It becomes constant at.

Then, this generated voltage is supplied to the pump current supply circuit 35, and the pump current value I _P is set so that the generated voltage is maintained at a predetermined constant value by the pump current supply circuit 35.
Is controlled. Therefore, at constant temperature, the current value I _P is almost proportional to the oxygen concentration in the exhaust gas.

Air-fuel ratio control circuit 32 is either rich or lean of the air-fuel ratio the target air-fuel ratio of the mixture supplied to the engine 21 in response to the pump current value I _P fed from the pump current supply circuit 35 to the oxygen pump element 4 Is determined. That is, when the pump current value I _P is equal to or lower than the reference value corresponding to the target air-fuel ratio, it is made rich, and when it is equal to or higher than the reference value, it is made lean. The intake secondary air is supplied to the intake manifold 23 by controlling the opening / closing of the electromagnetic opening / closing valve 26 according to the determination result, and the air-fuel ratio of the supplied mixture is feedback-controlled to the target air-fuel ratio.

The heater elements 6 and 7 are connected to the heater wire 6 through the lead wires 6d and (7d) by the heater current supply circuit 36 supplying the heater current between the takeout portions 6c and (7c).
b, (7b) is energized, the heater wires 6b, (7b) generate heat to heat the oxygen concentration detection element 3.

The supply of the heater current by the heater current supply circuit 36 is duty-controlled by the air-fuel ratio control circuit 32. The air-fuel ratio control circuit 32 supplies an I _H duty pulse representing the heater current value I _H to the heater current supply circuit 36.
Heater current supply circuit 36 is a heater wire 6b turned on by its I _H duty pulse to input I _H duty pulse as shown in FIG. 6, a switching transistor 39 for applying the battery voltage V _B in (7b).

Next, the procedure of the control method of the oxygen concentration sensor of the present invention executed by the air-fuel ratio control circuit 32 will be described with reference to the operation flow chart shown in FIG.

First, the air-fuel ratio control circuit 32 sets the atmospheric pressure P _A to 650 mmHg.
Whether the cooling water temperature T _W is 45 ° C. or less, the intake air temperature T _A is 20 ° C. or less, and the engine speed Ne is 300 rpm or less. Is determined (steps 51 to 54). P _A <is 650mmHg If during high altitude _running, a T W <45 ° C. If the low coolant _temperature, low intake air temperature If T A <20 ° C., The Ne
If it is <300 rpm, it is during engine cranking.
In such a state, it is necessary to stop the feedback control of the air-fuel ratio to the value in the lean range, so the air-fuel ratio control circuit 32 issues a pump current supply stop command to the pump current supply circuit 35 (step 55). ), also the duty ratio of I _H duty pulse so as to correspond to the I _{H =} 0 to stop the supply of the heater current in the 0% I _H
The supply of the duty pulse to the heater current supply circuit 36 is stopped (step 56). On the other hand, P _A ≧ 650 mm
Hg, T _W ≧ 45 ° C., T _A ≧ 20 ° C., Ne ≧ 300 r.
When all the conditions of pm are satisfied, the battery voltage V
It is determined whether _B is 14.7 V or higher (step 5).
7). If V _B ≦ 14.7 V, the internal time counter A (not shown) of the air-fuel ratio control circuit 32 has a counting time of 0.5 sec.
To start down counting (step 5
8). If V _B > 14.7 V, the battery voltage V _B is a high voltage, and therefore it is determined from the count value of the time counter A whether or not this high voltage state continues for 0.5 sec or more (step 59). When the high voltage state of the battery continues for 0.5 seconds or more, overpower is supplied to the heating elements 6 and 7 to thermally destroy the heater wires 6b and (7b), so that the supply of the heater current is stopped. Execute 55 and 56. When the high voltage state of the battery has not continued for 0.5 seconds or more, and after execution of step 58, it is determined whether or not the absolute intake pressure P _BA is smaller than 210 mmHg (step 6).
0). If P _BA ≧ 210 mmHg, engine speed Ne
Is 4000 rpm or more (step 61). When Ne> 4000 rpm, since it is in the first region, the intake air-fuel mixture amount of the engine 21 increases and the exhaust gas temperature may rise above the heat generation temperature of the heating elements 6 and 7. For protection, steps 55 and 56 are performed to stop the heater current supply. When Ne ≦ 4000 rpm, engine speed Ne
Is 3000 rpm or more (step 62). If Ne ≦ 3000 rpm, 10 seconds is set as the counting time in the internal time counter B (not shown) of the air-fuel ratio control circuit 32 and the down counting is started (step 63). Thereafter, a pump current supply command is generated for the pump current supply circuit 35 (step 64),
Further, the duty pulse having the set content for oxygen concentration detection (I _H ≠ 0) is supplied to the heater current supply circuit 36 (step 65). In step 60, P
If it is determined that _BA <210 rpm, the engine load is low, so step 64 is immediately executed. N
If e> 3000 rpm, that is, 4000 ≧ Ne>
If it is 3000 rpm, since it is in the second region, the air-fuel ratio control circuit 32 issues a pump current supply stop command to the pump current supply circuit 35 (step 66), and the state of this rotational speed range continues for 10 seconds or more. Whether or not it is determined from the count value of the time counter B (step 67). 4000
≧ Ne> 3000 rpm. 10 seconds in the speed range
When the above is continued, step 56 is executed to stop the supply of the heater current. The state of this speed range is 10se
If it has not continued for more than c, step 65 is executed. After executing step 65, the air-fuel ratio control circuit 32 corrects the heater current value I _{H according} to the battery voltage V _B (step 68). This correction is performed assuming that the standard voltage of the battery voltage V _B is Vr and the duty ratio T _OHE of the I _H duty pulse output from the air-fuel ratio control circuit 32 is 10.
It is performed by setting as _{0-K (V B -Vr)} . Here, K is a constant. As a result, the duty ratio T _OHE of the I _H duty pulse is set to 100% when the battery voltage V _B is low as shown in FIG. 8, and when the battery voltage V _B is equal to or higher than the predetermined voltage V ₁ , the voltage V
_The higher _B is, the smaller it is set.

In this way, the air-fuel ratio control circuit 32 controls the heater current value I _H by repeatedly executing the above steps.

Note that step 64 may not be executed when the pump current is already being supplied, and step 65 may not be executed when the heater current is being supplied. Further, in step 68, I _H output from the air-fuel ratio control circuit 32
The duty ratio T _OHE of the duty pulse is set to (Vr / V
_B ) × 100 may be set. As a result, the duty ratio T _OHE of the I _H duty pulse is set as shown in FIG. 9 almost in the same manner as in the case of FIG.

In the embodiment of the present invention described above, the air-fuel ratio is determined from the pump current value using the pump current value as the output signal of the oxygen concentration sensor, but the pump current value is controlled to a predetermined value to generate the battery element. The voltage may be used as the output signal of the oxygen concentration sensor, and in that case, the oxygen concentration sensor can be controlled as described above.

Further, in the above-described embodiment of the present invention, the engine load is discriminated from the engine speed, but the invention is not limited to this, and it may be discriminated from the intake absolute pressure, the throttle valve opening degree, or the like.

As described above, in the method for controlling the oxygen concentration sensor of the present invention, when the detected value of the engine operating parameter is in the first region, the current supply to the heating element is stopped and the detected value of the engine operating parameter is set to the first value. When the operating condition in the second region, which is smaller than the first region, continues for a predetermined time or longer, the current supply to the heating element is stopped. Therefore, even if the exhaust gas temperature rises above the heat generation temperature of the heating element when the engine is under heavy load, it is possible to avoid overheating the heating element due to the stop of the current supply to the heating element. Can be prevented. Further, since the current supply / stop of the current supply to the heating element is not frequently repeated, the heat generation temperature of the heating element is stabilized, and the output characteristic of the oxygen concentration sensor can be maintained at a desired characteristic. Therefore, if the air-fuel ratio control is performed using the oxygen concentration sensor of the control method of the present invention, the exhaust gas purification performance can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an air-fuel ratio control device to which the control method of the present invention is applied, FIG. 2 is a side view specifically showing an oxygen concentration sensor in the device of FIG. 1, and FIGS. 3 to 5 Is a diagram showing an internal configuration of the oxygen concentration sensor, FIG. 6 is a circuit diagram showing a specific configuration of a heater current supply circuit, FIG. 7 is an operation flow diagram showing a procedure of a control method of the present invention, FIG. 8 and FIG. FIG. 9 is a duty ratio setting characteristic diagram of the I _H duty pulse. Description of symbols of main parts 3 ... Oxygen concentration detection element 6, 7 ... Heating element 8 ... Gap 11 to 14 ... Electrode layer 17 ... Protective member 22 ... Throttle valve 23 ... Intake manifold 26 ... Solenoid on-off valve 27 ... Absolute pressure sensor 28 ... Rotation speed sensor 29 ... Cooling water temperature sensor 30 ... Oxygen concentration sensor 31 ... Exhaust manifold

Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location G01N 27/419 7363-2J G01N 27/46 327 Q (72) Inventor Minoru Muroya 1-chome, Wako-shi, Saitama No. 4 in Honda R & D Co., Ltd. (56) References JP 61-207960 (JP, A) JP 56-130650 (JP, A) JP 59-42963 (JP, U)

Claims (1)

[Claims] 1. An oxygen concentration detecting element, which is provided in an exhaust gas passage of an internal combustion engine and generates an output according to an oxygen concentration in the exhaust gas, and an oxygen concentration detecting element which generates heat when a current is supplied from a power source. A method for controlling an oxygen concentration sensor having a heating element for heating an internal combustion engine for detecting an engine operating parameter of the internal combustion engine, and supplying a current to the heating element when the detected value of the engine operating parameter is in a first region. When the detected value of the engine operating parameter is in the second region smaller than the first region, current is supplied to the heating element until the operating state continues for a predetermined time, For example, when the current supply to the heating element is stopped and the detected value of the engine operating parameter is in the area smaller than the first and second areas, the electric power to the heating element is reduced. The method of the oxygen concentration sensor, characterized by continuing the supply.