JPS61204559A - Measuring instrument for oxygen concentration - Google Patents

Abstract

PURPOSE:To improve the detection precision of exhaust oxygen concentration by setting the supply start timing of a pump current according the engine temperature at the start of an engine and the operation state after the start. CONSTITUTION:A measuring instrument is provided with an oxygen sensor (a) which has an element part supplied with a pump current correlating with the oxygen concentration in exhaust gas and a heater for heating the element part, a concentration measuring means (b) which supplies the pump current to the sensor (a) when inputting a start signal and detects the oxygen concentration in the exhaust gas from the current value, a temperature detecting means (c) which detects the engine temperature at the start of the engine, an operation state detecting means (d) which detects the operation state of the engine, and a starting period setting means (e) which powers on the heater of the sensor (a) when the engine is started and sets the output timing of the start signal according to the engine temperature at the start and the operation state after the start. Then, the supply start timing of the pump current is set by the means (e) according to outputs of the means (c) and (d) and it is judged properly that Ip-O2 correlation after the start is obtained to improve the durability of the sensor body and also improve the detection precision of the exhaust gas oxygen concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an oxygen concentration measuring device that detects the exhaust oxygen concentration of an automobile engine or the like using an oxygen sensor.

(Prior art) In recent years, in order to meet the demands for engine fuel efficiency and exhaust emissions, there has been a tendency for the air-fuel ratio to be feedback-controlled immediately after the engine starts. is detected as a parameter.

For this reason, oxygen sensors that can detect air-fuel ratios over a wide range from lynch to lean (for example, JP-A-59-67455
(see Japanese Patent Laid-Open No. 59-46350) have been developed. This type of oxygen sensor focuses on the characteristic that the diffusion-limited amount of oxygen correlates with the oxygen concentration when there is a predetermined potential difference between the sensor electrodes, and detects this as a diffusion current (pump current) using an external circuit. A wide range of fuel ratios are detected. Based on such oxygen sensor information G, the air-fuel ratio can be feedback-controlled over a wide range from rich to lean.

On the other hand, since the characteristics of an oxygen sensor depend on temperature, in order to stabilize its operation, a heater is provided to heat the sensor body (element part), and electricity is applied to the heater from the time the engine is started.

(Problems to be Solved by the Invention) However, in such a conventional oxygen concentration measuring device, a pump current that is related to the exhaust oxygen concentration t0 and has temperature dependent characteristics is supplied to the oxygen sensor, and this current value is Since the configuration is such that the air-fuel ratio is detected while the air-fuel ratio is being detected (the structure is similar to the embodiment described later, please refer to this), when the temperature of the sensor body changes, the air-fuel ratio detection accuracy decreases.

That is, the value of the pump current correlates with the oxygen concentration, and this correlation (hereinafter referred to as Ip-02 correlation) is established after the sensor body shifts to a predetermined active state. Particularly immediately after the engine is started, it is difficult to determine from what point the correlation becomes accurate. Therefore, in such a case, if the correlation is determined too early or if the feedback control information is used immediately after starting without considering the correlation, the engine operating performance will deteriorate. Furthermore, supply of pump current is started before transition to the active state, and the current value becomes excessive, promoting deterioration of the sensor body.

On the other hand, if the determination that the correlation is established is made later than necessary, the start of the feedback control will be delayed, resulting in a decrease in engine operating performance.

(Object of the Invention) Here, the present invention appropriately establishes the Ip-02 correlation after the engine starts by setting the pump current supply start timing according to the engine temperature at the time of engine start and the operating condition after engine start. The objective is to improve the accuracy of detecting exhaust oxygen concentration at the beginning of use while improving the durability of the sensor body.

(Structure of the Invention) The oxygen concentration measuring device according to the present invention has a basic conceptual diagram as shown in FIG.
As shown in the figure, an element section to which a pump current correlated to the oxygen concentration in exhaust gas is supplied, a heater that heats the element section,
An oxygen sensor a having a Temperature detection means C for detecting engine temperature
and an operating state detection means d for detecting the operating state of the engine.
and a start timing setting means e that energizes the heater of the oxygen sensor a when the engine starts, and sets the output timing of the start signal according to the engine temperature at the time of starting and the operating state after starting. , to appropriately determine whether the Ip-02 correlation is established after the engine is started.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 7 are diagrams showing one embodiment of the present invention, and are examples in which the present invention is applied to an air-fuel ratio control device for an engine.

First, to explain the configuration, in FIG. 2, 1 is an engine, intake air is supplied from an air cleaner 2 to each cylinder through an intake pipe 3, and fuel is injected by an injector 4 based on an injection signal St. Then, the exhaust gas combusted in the cylinder is introduced into the catalytic converter 6 through the exhaust pipe 5, and the harmful components (Co, I,
C.

NOx) is purified by a three-way catalyst and discharged.

The intake air flow 1iQa is detected by an air flow meter 7 and controlled by a throttle valve 8 in the intake pipe 3. The opening Cv of the throttle valve 8 is detected by a throttle valve opening sensor 9, and the rotation speed N of the engine 1 is detected by a crank angle sensor 10. Also, the temperature T of the cooling water flowing through the water jacket
w is detected by a water temperature sensor (temperature detection means) 11.

An oxygen sensor 12 is attached to the exhaust pipe 5, and the oxygen sensor! 2 is connected to an air-fuel ratio detection circuit (concentration measuring means) 13. The air-fuel ratio detection circuit 13 detects the oxygen sensor 1 when a start signal Sc is input under predetermined conditions (details will be described later).
A pump current 1p is supplied to the pump 2, and the current value is detected to output a voltage signal Vi corresponding to the exhaust oxygen concentration. The above air flow meter 7 and crank angle sensor l
O constitutes an operating state detecting means 14, and signals from the operating state detecting means 14 and each sensor 9, 11, 13 are input to a control unit 15. The control unit 15 controls the air-fuel ratio, controls the energization of the heater of the oxygen sensor 12, and controls the output of the start signal Sc based on the sensor information, and the detailed configuration will be described later.

FIG. 3.4 is an exploded perspective view and a sectional view of the oxygen sensor 12. In these figures, 21 is a substrate made of alumina, and on the substrate 21 is an air introduction plate 2 on which a channel-shaped air introduction part 23 is formed via a heater 22.
4 are stacked. A flat first solid electrolyte 25 having oxygen ion conductivity is laminated thereon, and a sensor anode (reference electrode) 26, which is an electrode exposed to the atmosphere, is placed on the bottom surface of the solid electrolyte 25, and a sensor anode (reference electrode) 26 is placed on the corresponding top surface of the solid electrolyte 25. A sensor cathode (measuring bridge) 27, which is an electrode exposed to exhaust gas, is provided by printing. Furthermore, a spacer plate portion having a thickness of L (about 0.1 mm) is laminated on top of this solid electrolyte 5, and a flat second solid electrolyte 2 is placed on top of this.
9 are stacked. These solid electrolytes 25, 29 and spacers 28 constitute an oxygen defining member 31 that covers the sensor cathode 27 and defines a gas introduction part (oxygen layer) 30 around the sensor cathode 27, and defines an oxygen layer. The component 31 limits the diffusion of oxygen molecules between the exhaust gas and the gas inlet 30. The above sensor anode 26, sensor cathode 2
7 and the solid electrolyte 25 constitute a sensor section 32, and the sensor section 32 outputs a voltage (hereinafter referred to as sensor voltage) Vs according to the oxygen partial pressure ratio between the atmosphere introduction section 23 and the gas introduction section 30. .

Further, a pump anode 33 and a pump cathode 34 as pump electrodes are provided on the upper and lower surfaces of the second solid electrolyte 29, respectively, and these pump anode 33, pump cathode 34, and solid electrolyte 4 constitute a pump section. . The pump section 35 controls the oxygen partial pressure of the gas introduction section 30 according to the value of the pump current 1p supplied between the pump electrodes. The sensor section 32, pump section 35, oxygen layer defining member 31, and atmosphere introduction plate 24 constitute an element section 36 that detects the oxygen concentration in exhaust gas. Note that when the heater voltage vh is applied to the heater 22, the solid electrolytes 25 and 29 are heated to an appropriate temperature and activated. Further, 41 and 42 are lead wires of the heater 22, and 43 to 46 are lead wires of the sensor anode 26, the sensor cathode 27, the pump anode, and the pump cathode 34, respectively.

FIG. 5 is a circuit diagram showing the configuration of the air-fuel ratio detection circuit 13, and in this figure, the air-fuel ratio detection circuit 13 is connected to the target voltage -V.
A voltage source 49 that generates a, a differential amplifier 50, a resistor R1,
It is composed of a current supply circuit 51, a current detection circuit 52, and an analog switch 53. The differential amplifier 50 compares the sensor voltage Vs with the target voltage -Va and calculates the difference value ΔV(Δ
Calculate V=Vs-(-Va)). Current supply circuit 5
1 flows out (or flows in) the pump current 1p from the pump cathode 34 of the element section 36 via the analog switch 53 so that the difference value ΔV becomes zero. That is, ΔV
When is positive, Ip is increased, and when is negative, Ip is decreased.

When the start signal Sc is input from the control unit 15, the analog switch 53 closes its contact to allow the passage of the pump current 1p, and when the start signal Sc is not input, the analog switch 53 opens its contact to prevent the passage of the pump current 1p. The current detection circuit 52 converts the pump current 1p into a voltage Vi (Vioclp) based on the potential difference between both ends of the resistor R1, and detects the voltage Vi (Vioclp).

Note that the pump current ip is positive (Vi
(also positive), and the opposite direction shown by the dashed arrow is negative.

Then, the target voltage -Va is set to the gas introduction section 30 of the element section 36.
The current detection circuit Pump current r detected by 52
The detected voltage Vi, which is proportional to p, uniquely corresponds to the air-fuel ratio, as shown in FIG. Therefore, by using this detection voltage Vi, the air-fuel ratio can be detected continuously and accurately over a wide range from the rich region to the lean region.

Referring again to FIG. 2, the control unit 15 has a function as an opening timing setting means, and includes a CPU 56, a ROM
57, RAM 58 and [10 port 59]. The CPU 56 reads necessary external data from the 11059 according to the program written in the ROM 57, performs arithmetic processing while exchanging data with the RAM 58, and transfers the processed data as necessary to the I10 port. Output to 59. The I10 port 59 is connected to an air-fuel ratio detection circuit 13 and a sensor group 9.11.
14 is input, and I10 port 5
9 outputs an injection signal Si, a heater signal sh and a start signal Sc. The ROM 57 stores calculation programs for the CPU 56, and the RAM 58 stores data used in calculations in the form of a map or the like. The heater signal sh is input to the amplifier 60, which amplifies the voltage of the signal sh and outputs the heater voltage vh to the oxygen sensor 1.
The voltage is applied to the heater 22 of No. 2.

Next, the effect will be explained.

Figure 7.8 is a flowchart showing the oxygen sensor control program written in the ROM 57.
, -PH indicate each step of flowchart 1.

FIG. 7 shows a detection start timing calculation program, and this program is repeatedly executed at irregular intervals during interrupt processing in bank ground jobs (BGJ).

First, at P, the rotational speed N is the starting determination rotational speed (400r, p
, m, ), and determine whether N≦40Or,
If p or m, it is determined that the start has not been completed yet, and the
2 and P3, the output of the heater signal sh and start signal Sc is stopped (if already stopped, the stopped state is maintained), and the process returns. On the other hand, N > 40Or, p, m
, it is determined that the start has been completed, and it is determined in P4 whether or not the heater signal sh is output. If the heater signal sh is not being output, first start outputting the same signal sh at P, and then P6.
At step P7, the cooling water temperature TW at that time (at the time of starting) is read, and at step P7, the output start timing Tst of the start signal Sc is looked up in a table based on this cooling water temperature Tw.

The output start timing 'l'st is the timing at which the oxygen sensor 12 starts detecting the exhaust oxygen concentration, and is set in the form of the elapsed time from the time when the output of the heater signal sh starts. The optimum value of this 'l'st value is stored in advance as a data table according to the engine salinity at startup (in this example, the cooling water temperature Tw), and the lower the cooling water temperature Tw, the larger the value is set. Ru.

Next, the rotational speed N and the basic injection amount 'rp are read at P. The basic injection amount Tp is calculated according to the following equation (2) by another routine (not shown).

Tp=-Qa/N---.-■ Where, K: constant, and P looks up the subtraction value Tsub to be subtracted from the output start timing Tst at regular time intervals based on N and Tp. This subtraction value Tsub is used in a program to be described later, and is set to a larger value in an operating range where the exhaust gas temperature is higher and the exhaust flow velocity is lower. This is because immediately after startup, the exhaust temperature is still relatively low, so the amount of exhaust air cooling is greater than the exhaust heat warming the oxygen sensor 12, and if the exhaust gas flow rate is high, the cooling effect is This is done in consideration of the fact that it does not get very warm.

Further, when it is determined in step P4 that the heater signal sh has already been output, the process jumps to P8 and sequentially looks up the subtraction value Tsub according to the operating state (for each look amplifier). Therefore, when the engine 1 has finished starting and the temperature inside the exhaust pipe 5 is in the process of rising, the heater 22 of the oxygen sensor 12 starts to be energized.
Durability is improved by avoiding a sudden temperature rise of the heater 22 alone.

Incidentally, for example, if only the heater 22 suddenly rises in temperature,
1tJ, which causes a decrease in durability due to peeling of the heating element! It's across the street.

FIG. 8 shows a detection start timing execution program, and this program is executed once every predetermined time. Note that this may be performed in synchronization with the engine rotation, for example, once every rotation.

Determine whether the start signal Sc is output based on the pH,
If it is not output, output start timing TS is determined by PI3.
Calculate t according to the following formula (■).

Ts t =Ts t' -Ts u b----
-■ However, Ts t : Value of output start timing of current routine Tst' : Value of output start timing of previous routine Next, PI3 determines whether Tst has become zero,
When Tst≦O, it is determined that it is the detection start timing, and a start signal Sc is output at P, 4.

As a result, the pump current rp by the air-fuel ratio detection circuit 13
The supply of air is started, detection of the air-fuel ratio is started, and feed control of the air-fuel ratio is started. At this time, the main body of the oxygen sensor 12 is sufficiently heated by the exhaust heat and the heat generated by the heater 22 and is in an active state, and the Ip-0□ correlation is established. Therefore, the air-fuel ratio is appropriately controlled using highly accurate air-fuel ratio detection information, and the operability of the engine 1 is improved.

Further, when Tst>0, the routine bypasses PI3 and returns, and the flow continues in this routine until Tst≦0. On the other hand, if the start signal Sc has already been output at the step pH, the program is repeated without going through the routine (P12 to P, 4).

In this way, first, Tst is determined by the cooling water temperature TV at startup.
After setting the magnitude of supply will begin. therefore,
Excessive increase in pump current Ip at the start of supply is avoided, deterioration of the element section 36 is suppressed, and its durability is improved.

Furthermore, it can be used as accurate air-fuel ratio detection information immediately from the start of supply of the pump current Ip, improving feedbank control accuracy and improving drivability. That is, it is possible to appropriately determine whether the Ip-02 correlation is established and obtain accurate air-fuel ratio detection information in the minimum amount of time immediately after starting.

Note that the present invention is not limited to the type of oxygen sensor shown in the above embodiments. In short, oxygen molecules are pumped so that the diffusion current is correlated with the oxygen concentration in the exhaust gas, and the air-fuel ratio is calculated based on comparison with a reference gas (not necessarily just the atmosphere) with a constant oxygen concentration. It can be applied to all types. Therefore, it goes without saying that a part of the pump electrode may be shared with the sensor electrode, or that the sensor section and the pump section may be of an integrated structure (apparently only the sensor section).

(Effects) According to the present invention, the supply of pump current can be started by appropriately determining whether the Ip-02 correlation is established after the engine is started, and the durability of the sensor body can be improved while the exhaust gas at the beginning of use can be improved. The detection accuracy of oxygen concentration can be improved.

[Brief explanation of drawings]

Fig. 1 is a basic conceptual diagram of the present invention, Figs. 2 to 8 are diagrams showing an embodiment of the present invention, Fig. 2 is an overall configuration diagram thereof, and Fig. 3 is a diagram showing an embodiment of the present invention.
The figure is an exploded perspective view of the oxygen sensor, Figure 4 is a sectional view of the oxygen sensor, Figure 5 is a circuit diagram of the air-fuel ratio detection circuit,
Figure 6 is a diagram showing the relationship between the air-fuel ratio and the detected voltage.
The figure is a flowchart showing a program for calculating the detection start timing, and FIG. 8 is a flowchart showing a program for executing the detection start timing. 1-----1 engine, 11--1 water temperature sensor (temperature detection means), 12--.
...-Oxygen sensor, 13-----1 Air-fuel ratio detection circuit (concentration measuring means), 1
4--- Operating state detection means, 15-- Control unit ([5i'l Start IFI setting means).

Claims (1)

[Claims] a) an oxygen sensor having an element section to which a pump current correlated to the oxygen concentration in exhaust gas is supplied and a heater that heats the element section; b) when a start signal is input, the oxygen sensor a concentration measuring means for supplying a pump current to the sensor and detecting the oxygen concentration in the exhaust gas based on the value of the pump current; c) a temperature detecting means for detecting the engine temperature at the time of engine startup; d) engine operation. an operating state detection means for detecting the state; and e) a start timing for energizing the heater of the oxygen sensor when the engine starts and setting the output timing of the start signal according to the engine temperature at the time of starting and the operating state after starting. An oxygen concentration measuring device comprising: a setting means;