JPS61122559A - Instrument for measuring oxygen concentration - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the function of an oxygen sensor in the oxygen sensor consisting of an element part for detecting and heater by increasing the electric power supply to the heater when the oxygen concn. is at the prescribed concn. or above to burn the accumulated deposit. CONSTITUTION:The oxygen sensor (a) is constituted of the element part for detecting oxygen concn. and the heater for heating the element part and is provided in the exhaust pipe of an engine, etc. Diffusion current is changed according to the oxygen concn. and the oxygen concn. is detected from the current value thereof in order to detect continuously an air-fuel ratio. However, the carbon, hydrocarbon, etc. in the exhaust gas stick to the element part. The state in which the oxygen concn. in the measuring gas is larger than the prescribed concn. in then discriminated by a discriminating means (b) and a signal is fed to a means (c) for controlling the heater, by which the electric power to the heater is increased to burn the deposit sticking to the element part. Since the deposit accumulating on the oxygen sensor is burned, the deterioration in the function of the oxygen sensor is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an oxygen concentration measuring device, and more particularly to an oxygen concentration measuring device that accurately detects the oxygen concentration of a gas to be measured over a wide range 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 trend toward feedback control of the air-fuel ratio even in the lean region. Detected as a parameter by an oxygen sensor.

For this reason, it is possible to detect air-fuel ratios over a wide range from rich to lean.
However, in such conventional oxygen concentration measuring devices, the main part of the oxygen sensor is directly exposed to exhaust gas. When an oxygen sensor is exposed to combustion exhaust gas with a rich air-fuel ratio for a long time, unnecessary substances such as carbon and HC components in the exhaust gas (hereinafter referred to as unnecessary deposits) tend to accumulate on its surface, electrodes, and the like. That is, although such an oxygen sensor can perform feedback control to a rich air-fuel ratio, there is a possibility that this control state to a rich air-fuel ratio may continue for a long time, and in such a case, the above-mentioned deposition is likely to occur. For this reason, there is a risk of clogging of the surface of the oxygen sensor, current leakage between the electrodes, etc., and it is expected that the air-fuel ratio detection accuracy will decrease and the air-fuel ratio control accuracy will deteriorate.

(Object of the Invention) Therefore, the present invention provides that when the inside of the exhaust pipe reaches a predetermined oxygen concentration or higher (for example, a predetermined lean air-fuel ratio), by increasing the power supplied to the heater of the oxygen sensor for a predetermined period of time,
The purpose is to increase the heat generated by the heater to burn off unnecessary deposits that have accumulated on the oxygen sensor, thereby preventing the oxygen sensor from deteriorating in function.

(Structure of the Invention) The overall configuration diagram of the oxygen concentration measuring device according to the present invention is shown in FIG.
As shown in the figure, an oxygen sensor a has an oxygen concentration detection element section that detects the oxygen concentration in exhaust gas, a heater that heats the element section, and a state where the gas to be measured has a predetermined oxygen concentration abnormality. determination means for determining whether or not the oxygen concentration is present, and outputting a heating increase signal for a predetermined period of time when a predetermined oxygen concentration is abnormal; and heater control means for increasing power supplied to the heater when the heating increase signal is manually inputted. C, which incinerates unnecessary deposits on the oxygen sensor a.

(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 a device for detecting the oxygen concentration in the exhaust gas of an engine, that is, the air-fuel ratio.

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, H,
ClN0x) is purified by a three-way catalyst and discharged.

The intake air flow rate Qa is detected by an air flow meter 7 and controlled by a throttle valve 8 in the intake pipe 3. The temperature Tw of the cooling water flowing through the water jacket is determined by the water temperature sensor 9.
The oxygen concentration in the exhaust gas is detected by the oxygen sensor 10. Further, the rotation speed N of the engine 1 is detected by a crank angle sensor 11. Each of these sensors 7
．． The signal from 9.10.11 is control unit 1
2, and the control unit 12 performs air-fuel ratio control and energization control to the heater of the oxygen sensor 10 based on these 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 10. In these figures, a substrate 21 is an insulating substrate, and an air introduction plate 24 on which a channel-shaped air introduction portion is formed is formed via a heater 22.
are stacked. A plate-shaped solid electrolyte 25 having oxygen ion conductivity is laminated thereon, and a reference electrode 26 is provided on the lower surface of the solid electrolyte 25, and a pump electrode 27 and a sensor electrode 28 are provided on the corresponding upper surface by printing. Further, a plate-like body 30 having a window-shaped gas introduction part 29 for introducing exhaust gas is laminated on top of the solid electrolyte 25, and is placed on top of the plate-like body 30 to restrict gas diffusion (for example, when lean, diffusion in the direction of the arrow is Plate-shaped bodies 32 provided with small holes 31 as a means for regulating the amount of water are laminated. In addition, 33.34 is heater 2
Lead wires 35 to 37 are lead wires for the reference electrode 26, pump electrode 27, and sensor electrode 28, respectively.

The pump electrode r and the reference electrode 26 constitute electrodes for flowing a pump current Ip that causes the movement of oxygen ions in the solid electrolyte 25 and keeps the oxygen partial pressure ratio between the upper and lower surfaces constant. This constitutes an electrode for detecting the voltage generated by the oxygen partial pressure ratio between both sides of the solid electrolyte 25. The atmosphere introducing plate 24, the solid electrolyte, the reference electrode 26, the pump electrode 27, the sensor electrode 28, the plate-shaped body 30, and the plate-shaped body 32 constitute an element section 38 for detecting the oxygen concentration in the exhaust gas.

FIG. 5 is a block diagram showing the +yt structure of the control unit 12. In this figure, the control unit 7 12 includes an air-fuel ratio detection circuit 41, a switch circuit 42,
It is composed of A/D converters 43 to 46, a driver circuit 47, and a microcomputer 48.

The air-fuel ratio detection circuit 41 includes a voltage source 49 that generates a target voltage -Va, a differential amplifier 50, a resistor R1, and a current supply circuit 51.
and a current detection circuit 52. The differential amplifier 50 serves as the reference electrode 2 in the element section 38 of the oxygen sensor 10.
6, the potential of the sensor electrode 28 (hereinafter referred to as sensor voltage) Vs is compared with the target voltage (-Va), and the difference value (
ΔV) (ΔV=Vs−(−Va)) is calculated. The current supply circuit 51 flows out (or flows into) the pump current Ip from the pump electrode 27 of the element section 38 so that the difference value Δ■ becomes zero. That is, when ΔV is positive, Ip is increased, and when ΔV is negative, Ip is decreased. The current detection circuit 52 is a resistor R.
1, the pump current Ip is changed to the voltage Vt(
V i QCT p ) and detected. Note that the pump current Ip is positive in the direction shown by the solid arrow (Vi is also positive),
The opposite direction indicated by the dashed arrow is negative.

Then, the target voltage va is set to 1 when the oxygen concentration in the gas introduction section 29 of the element section 38 is maintained at a predetermined value.
That is, it is set to a value corresponding to the sensor voltage Vs when the oxygen partial pressure ratio between both surfaces of the solid electrolyte 25 reaches a predetermined value (in particular, the detection voltage proportional to the pump current rp detected by the current detection circuit 52 is set to Vi corresponds uniquely to the air-fuel ratio as shown in Figure 6. Therefore, by using this detection voltage Vt, the air-fuel ratio can be continuously and precisely controlled over a wide range from the rich region to the lean region. can be detected.

The switch circuit 42 has a function as a heater control means, and is composed of a transistor Q1, for example, as shown in FIG. The transistor Q1 has a conduction control signal sh of (H
), it is turned on and supplies the DC voltage vb from the battery 53 to the heater n of the oxygen sensor 10, and when it is [L], it is turned off and the supply is stopped. The energization control signal sh is a signal whose duty is controlled within a predetermined period for the time when the energization control signal sh becomes [H].As will be described later, when the air-fuel ratio reaches a predetermined lean air-fuel ratio, the time when the energization control signal sh becomes [H] becomes longer. The amount of heat generated by the heater 22 is increased. That is, when the air-fuel ratio reaches a predetermined lean air-fuel ratio, the on-duty period of the transistor Q1 within a predetermined cycle becomes longer. In this embodiment, the energization control signal sh when the on-duty period becomes longer under the above-mentioned conditions corresponds to the heating increase signal. The A/D converters 43 to 45 A/D convert the signals from the air-fuel ratio detection circuit 41, the air flow meter 7, and the water temperature sensor 9, respectively, and the A/D converter 46 converts the DC voltage vb of the battery 53 into A/D. Dim and output to the microcomputer 48.

Further, the driver circuit 47 amplifies the injector drive pulse Pi corresponding to the fuel injection amount output from the microcomputer 48 into an injection signal Si that enables the injector 4 to operate, and outputs the amplified signal.

The microcomputer 48 has a function as a determining means, and is composed of a CPU 55, a ROM 56, a RAM 57, an NVM (nonvolatile data memory) 58, and an I10 board 59. The CPU 55 takes in necessary external data from the I10 port 59 according to the program written in the ROM 56, and also imports necessary external data from the RAM 57 and N
Arithmetic processing is performed while exchanging data with the VM58, and the processed data is sent to I10 port 5 as necessary.
Output to 9. ■10 port 59 has A/D converter 43
-46 and the signals from the operating state detection means 13 are inputted, and the injector drive pulse Pi and the energization control signal sh are outputted from the 110 port 59. R
The OM 56 stores a calculation program for the CPU 55, and the RAM 57 and NVM 58 store data used in calculations in the form of a map or the like.

Next, the effect will be explained.

In general, oxygen sensors are used to measure exhaust gases that are at high temperatures and are mixed with carbon components, etc., and are subject to harsh measurement environments. Further, for example, in order to continuously detect the air-fuel ratio, a unique structure is required, such as changing the diffusion current (pump current) according to the oxygen concentration. Conventionally, emphasis has been placed on the function of detecting the air-fuel ratio, which is somewhat insufficient in terms of maintaining a good detection posture under harsh environments.

Therefore, in this example, we focused on the fact that the main cause of the decrease in the detection accuracy of the oxygen sensor is the adhesion of carbon and HC components, and estimated and determined this under conditions in which adhesion of carbon, etc. is expected. When it is determined that the unnecessary deposits have adhered or accumulated, the power supplied to the heater 22 of the oxygen sensor 10 is increased to burn off and remove the unnecessary deposits.

FIG. 8 is a flowchart showing a heater energization control program written in the ROM 56.
P1 indicates each step of the flowchart. This program is executed once every predetermined time.

First, at P, it is determined whether the current operating range is a rich operating range from the basic injection amount 'rp and the final injection amount Ti calculated in another routine (as shown). These injection amounts TP and Ti are calculated according to the following equations (1) and (2), respectively.

T p −K X Q a / N ・
----1 ■ However, K: Constant Ti-Tp Furthermore, in equation 0, cOEF is various increase coefficients, and is used to perform various increase corrections on the basic injection amount Tp based on, for example, the cooling water temperature Tw. α is an air-fuel ratio correction coefficient when performing feedback control of the air-fuel ratio to the target air-fuel ratio, and TS is a coefficient for correcting a response delay (dead time) of the injector 4.

When the engine is in the rich operating range, the count value C1 of the rich counter is compared with the predicted adhesion value Go at P2. The rich counter counts the time elapsed since the air-fuel ratio started being controlled to the rich side, and its count value C is incremented each time this routine is executed. When C1<Co, the rich counter is incremented in P3 and CI
≧C.

When it becomes 1, it is determined that unnecessary deposits have accumulated on the oxygen sensor 10, and the incineration flag FH is set in P4 and the process returns.

The incineration flag FH increases the power supplied to the heater 22 (
In other words, it indicates whether or not to incinerate unnecessary deposits by outputting a heating increase signal.
1) and is reset (FH=O) when it does not increase. Therefore, when the incineration flag FH is set at P4, it is predicted that unnecessary deposits will accumulate on the oxygen sensor 10, and a flow will flow to incinerate this when the air-fuel ratio shifts to a predetermined lean air-fuel ratio, as described below. .

That is, when Pl is not in the rich operating range, P determines whether or not the incineration flag FH is set. F
When H=0, the energization control signal sh is output at P6, and the count value C2 of the incineration counter is cleared at P7 (
C2=0) and return. On the other hand, when FH=1, it is determined in P8 whether the current operating range is in a predetermined lean operating range, and if it is not in the predetermined lean operating range, the process jumps to P6. Also, if it is in a predetermined lean operating range, P.

The count value c2 of the incineration counter is compared with the incineration completion count value CO2. The incineration counter is a counter that measures the incineration period (the output period of the heating increase signal), and the incineration period is set to a predetermined value within the range in which unnecessary deposits can be incinerated.

Note that this value Co2 and the above-mentioned adhesion predicted value Co may be mutually related and set to appropriate fixed values or variable values that change depending on the operating conditions.

Now, when C2<Co at P, a heating increase signal is output at P, 3 to increase the calorific value of heater n, the incineration counter is incremented at Pl+, and the process returns. This allows the oxygen sensor 10 to
is further heated and the incineration of the accumulated unnecessary deposits begins. When the count value C2 becomes 02≧CO□, it is determined that the incineration of unnecessary adhesion is completed, and the incineration flag FH is reset in PI2, and the rich counter is cleared (C, = 0) in PI3, and the Proceed to.

In this way, after a predetermined period of time has elapsed in the rich operation region where unnecessary deposits are expected to accumulate, the power supplied to the heater 22 is increased when the next lean operation region is entered, and the unnecessary deposits are incinerated. After incineration, normal heater energization control is executed again. Therefore, it is possible to prevent the oxygen sensor 10 from deteriorating in function, and it is possible to avoid deteriorating the accuracy of air-fuel ratio control. In this case, the incineration is limited to only when accumulation of unnecessary deposits is predicted, so that the heater power is not increased unnecessarily and wasteful power consumption can be avoided.

Note that the predetermined lean operating range may include the engine cut range and the engine stop period.

Further, the present invention is not limited to the type of oxygen sensor shown in the above embodiments, but can be applied to any type of oxygen sensor as long as it has a heater.

(Effects) According to the present invention, unnecessary deposits deposited on the oxygen sensor can be incinerated, and deterioration in the function of the oxygen sensor can be prevented.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the present invention, FIGS. 2 to 8 are diagrams showing an embodiment of the present invention, FIG. 2 is a schematic configuration diagram thereof, and FIG.
Figure 4 is an exploded perspective view of the oxygen sensor, Figure 4 is a sectional view of the oxygen sensor, Figure 5 is its block diagram, Figure 6 is a diagram showing the relationship between the air-fuel ratio and detected voltage, and Figure 7. is a detailed circuit diagram of the switch circuit, and FIG. 8 is a flowchart showing the heater energization control program. 1----1 engine, 10・----1 oxygen sensor, 12-・・control unit (discrimination means), 42-
111.-Switch circuit (heater control means).

Claims (1)

[Scope of Claims] a) an oxygen sensor having an oxygen concentration detection element section that detects the oxygen concentration of a gas to be measured and a heater that heats the element section; b) when the gas to be measured has a predetermined oxygen concentration or higher c) determining means for determining whether or not the oxygen concentration is present, and outputting a heating increase signal for a predetermined time when the oxygen concentration is higher than a predetermined oxygen concentration; and c) increasing power supplied to the heater when the heating increase signal is input. An oxygen concentration measuring device comprising: a heater control means;