JPS61129563A - Instrument for measuring oxygen concentration - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an oxygen sensor by detecting the increase of the oxygen concn. in an exhaust pipe to the prescribed oxygen concn. or above, for example, the atm. state by means of an oxygen sensor and stopping the pump current to the oxygen sensor when an engine stops. CONSTITUTION:The oxygen sensor (a) is provided in the exhaust pipe of an internal-combustion engine and the concn. is measured by a means (b) for measuring the oxygen concn. The sensor (a) is so constituted that one side of an oxygen ion conductive electrolyte contacts with the atm. air and the other side contacts with the exhaust gas. The pump current is passed to the sensor so as to maintain the specified oxygen partial pressure ratio on both sides thereof and the oxygen concn. is detected from the pump current value by the means (b). The signal to stop the pump current is emitted from a means (c) for generating the stop signal to stop the current on discrimination that the atmosphere of the oxygen sensor is in the state above the prescribed oxygen concn. when the internal-combustion engine stops. The supply of the overcurrent for a long period is thus obviated and the deterioration of the oxygen sensor is thus prevented as the pump current is stopped while the atmosphere of the oxygen sensor is above the prescribed oxygen concn.

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 prevents deterioration of 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.

For this reason, various oxygen sensors have been developed that are capable of detecting air-fuel ratios over a wide range from rich to lean (see, for example, Japanese Patent Laid-Open No. 59-67455 and Japanese Patent Laid-Open No. 59-46350). This kind of oxygen sensor focuses on the characteristic that the diffusion limit oxygen amount is correlated with the oxygen concentration when there is a predetermined potential difference between the sensor electrodes, and by detecting this as a diffusion current (pump current), the oxygen concentration (i.e. Air-fuel ratio)
is being detected.

However, in such conventional oxygen concentration measuring devices, a pump current that correlates with oxygen concentration is supplied to the oxygen sensor, and the air-fuel ratio is detected from this current value, so the air-fuel ratio shifts to the lean side. The pump current value increases accordingly. Therefore, when the inside of the exhaust pipe is in a state close to that of air, the value of the pump current is at its maximum, and if such a state continues for a long time, the oxygen sensor will deteriorate. In particular, if the ignition switch is left in the ON position before starting the engine, or if the ignition switch is left in the ON position when the engine stalls, the pump current will continue to be supplied even though the inside of the exhaust pipe is close to the atmosphere. and the above deterioration is likely to be accelerated.

(Purpose of the Invention) Therefore, the present invention detects whether the atmosphere of the oxygen sensor (for example, inside the exhaust pipe) is in a state (for example, atmospheric state) of a predetermined oxygen concentration or higher, and By stopping the supply of pump current to the oxygen sensor when the condition is present.

Oxygen 1 by avoiding long-term supply of excessive pump current
The purpose is to prevent sensor deterioration.

(Structure of the Invention) The oxygen concentration measuring device according to the present invention, as shown in FIG. The concentration measuring means detects the oxygen concentration of the gas to be measured based on the value of the pump current supplied to the pump, and stops supplying the pump current when a stop signal is input.When the engine is stopped, the atmosphere of the oxygen sensor a is stop signal generating means C that determines whether or not the oxygen concentration is above a predetermined oxygen concentration and outputs the stop signal when the oxygen concentration is above the predetermined oxygen concentration, thereby avoiding supply of excessive pump current. It is something to do.

(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 through an intake pipe 3 to each cylinder, and fuel is injected by an injector 4 based on an injection signal Si. Then, the exhaust gas burned in the cylinder is introduced into the catalytic converter through the exhaust pipe 5, and the harmful components (Go,
H.C.

NOx) 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 detected by a water temperature sensor 9, and the oxygen concentration in the exhaust gas is detected by an oxygen sensor 10. Further, the rotation speed N of the engine 1 is detected by a crank angle sensor 11, and the operation status of the ignition switch is detected by a switch sensor 12. Signals from each of these sensors 7.9.10.11.12 are input to the control unit 13, and the control unit 13 controls the air-fuel ratio and the energization of the heater of the oxygen sensor 10 based on the sensor information. 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, reference numeral 21 denotes an insulating substrate, and an air introduction plate 24 having a channel-shaped air introduction portion 23 formed thereon is laminated on the substrate 21 via a repeater 22 . 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 the heater 22
The lead wires 35 to 37 are respectively reference electrodes 26. These are lead wires for the pump electrode 27 and sensor electrode 28. The pump electrode 27 and the reference electrode 26 constitute a pump electrode 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, and the sensor electrode 28 and the reference electrode 26 constitutes a sensor electrode for detecting the voltage generated by the oxygen partial pressure ratio between both surfaces of the solid electrolyte 25. And the above-mentioned atmosphere introduction plate 24. Solid electrolyte 25, reference electrode 26, pump electrode 27. The sensor electrode 28, the plate-like body 30, and the plate-like body 32 constitute an element section 38 that detects the oxygen concentration in exhaust gas.

FIG. 5 is a block diagram showing the configuration of the control unit 13. In this figure, control unit 1
3 is an air-fuel ratio detection circuit 41. Switch circuit 42.43, A
/D converters 44-471. It is composed of a driver circuit 48 and a microcomputer 49.

The air-fuel ratio detection circuit 41 has a function as a concentration measuring means, and includes a voltage source 50 that generates a target voltage -Va, and a differential amplifier 5.
1. Resistor R1, current supply circuit 52 and current detection circuit 5
Consisting of 3. The differential amplifier 51 is the oxygen sensor 10
The potential of the sensor electrode 28 (hereinafter referred to as sensor voltage) Vs with respect to the reference electrode 28 in the element section 38 is compared with the target voltage -Va, and the difference value ΔV (ΔV=V s -(-
Calculate V a)). The current supply circuit 52 flows out (or flows into) the pump current IP from the pump electrode 27 of the element section 38 so that the difference value ΔV becomes zero. That is, Δ
When V is positive, the current p is increased, and when it is negative, Ip is decreased.The current detection circuit 53 converts the pump current IP into a voltage Vi (VioCIp) based on the potential difference between both ends of the resistor R1, and detects it. Note that the pump current Ip is positive in the direction indicated by the solid arrow (Vi is also positive), and negative in the opposite direction indicated by the broken arrow.

Then, the target voltage -Va is set to the gas introduction section 29 of the element section 38.
The current supply circuit The detected voltage Vi proportional to the pump current IP detected by the pump 52 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.

The switch circuit 42 is turned ON when the heater energization signal sh is input, and supplies the DC voltage vb from the battery 54 to the heater 22 of the oxygen sensor IO, and stops the supply when the heater energization signal sh is not input.

The heater energization signal sh is sent to the microcomputer 49, which will be described later.
When the ignition switch is operated to the start position, the output is output, and the output continues until the ignition switch is turned off. The heater 22 has a DC voltage vb
When supplied, the switch circuit 43 generates heat and activates the element section 38. Furthermore, the switch circuit 43 is constituted by, for example, an analog switch, and is turned ON when the power supply signal Sd is input, and outputs the DC voltage vb to the air-fuel ratio detection circuit. 41 and the power signal S
When d is not input, the supply is stopped. In this case,
The state in which the output of the power signal Sd is stopped corresponds to the output of a stop signal, and the state in which the power signal Sd is output is equivalent to the stop in the output of the stop signal. In this embodiment, for convenience, a form of power supply signal Sd is used in the opposite relationship to that of the stop signal. When the air-fuel ratio detection circuit 41 is supplied with the DC voltage vb, it starts feedback control of the pump current Ip to the oxygen sensor 10, detects the air-fuel ratio, and outputs the detection voltage Vi, and the supply of the DC voltage vb is stopped. Then, the feedback control of the pump current Ip is stopped.

Each of the A/D converters 44 to 46 has an air-fuel ratio detection circuit 41.
．． Each signal from the air flow meter 7 and the water temperature sensor 9 is A/D converted, and the A/D converter 47 A/D converts the DC voltage vb of the battery 54 to the microcomputer 49.
Output to. Further, the driver circuit 48 amplifies the injector drive pulse Pi corresponding to the injection amount of fuel output from the microcomputer 49 into an injection signal Si that enables the injector 4 to operate, and outputs the amplified signal Si.

The microcomputer 49 has a function as a stop signal generating means, and includes a CPU 55, a ROM 56 . RAM57,N
It is composed of a VM (non-volatile data memory) 58 and an engineering/○ board 59. The CPU 55 imports necessary external data from the I10 boat 59 according to the program stored in the ROM 56, and also imports necessary external data from the RAM 5.
The 6D10 port 60 performs arithmetic processing while exchanging data with the 6D10 port 60 and N V M2R, and outputs the processed data to the I10 port 59 as necessary.
Signals from /D converters 44 to 47, crank angle sensor 11 and switch sensor 12 are input, and I
The injector drive pulse Pi, heater energization signal sh, and power supply signal Sd are output from the 10 port 60. 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 that detect the diffusion-limited amount of oxygen when there is a predetermined potential difference between the sensor electrodes as a pump current that correlates to the oxygen concentration in the exhaust gas can continuously detect the air-fuel ratio over a wide range. On the other hand, as the air-fuel ratio shifts to the leaner side, the value of the pump current must increase. In such a case, since the pump current is continuously supplied, if its value becomes large, it will accelerate the deterioration of the pump electrode and the solid electrolyte.

Therefore, in this embodiment, the state in which the inside of the exhaust pipe becomes atmospheric is determined to be when the engine is stopped, and when the engine reaches the stopping speed, the pump current I
By stopping the supply of p, deterioration of the oxygen sensor is prevented.

FIG. 7 is a flowchart showing the program for pump current supply control written in the ROM 56.
1 to P4 indicate each step of the program. This program is executed once every predetermined time.

First, the engine rotation speed N is read in P, and it is set to a predetermined stop determination rotation speed Nt in P2 (for example, N t = 1
0Orpm). When N≧N6, it is determined that it is not in a stopped state and there is no atmosphere inside the exhaust pipe 5, and the power supply is turned on at P.
d (if it has already been output, maintain that state). As a result, the air-fuel ratio detection circuit 41 performs feedback control on the pump current Ip, and the microcomputer 49
The air-fuel ratio is controlled to a predetermined target air-fuel ratio. on the other hand,
When P2 is Nt, it is determined that the exhaust pipe 5 is transitioning to a stopped state and the inside of the exhaust pipe 5 is transitioning to a state almost close to the atmosphere, and P.
The output of the power signal Sd is stopped. As a result, feedback control of the pump current Ip is stopped. Therefore, unlike in the past, excessive pump current Ip is not unnecessarily supplied, and deterioration of the pump electrodes and solid electrolyte can be prevented.
For example, even if the ignition switch is left in the ON position or the engine stalls, the supply of the pump current Ip is immediately stopped, so deterioration of the oxygen sensor 10 can be prevented.

In addition, in this embodiment, the state in which the inside of the exhaust pipe 5 becomes atmospheric is performed using the rotation speed N as a parameter, but the present invention is not limited to this. In short, it is only necessary to be able to determine that the atmosphere of the oxygen sensor 10 is close to the atmosphere, and the determination may be made based on, for example, a twin cut signal or the like.

Furthermore, the present invention is not limited to the type of oxygen sensor shown in the above embodiment, but can be applied to any oxygen sensor that utilizes the characteristic that the value of the pump current correlates with the oxygen concentration of the gas to be measured. 6 (Effects) According to the present invention, when the atmosphere of the oxygen sensor has a predetermined oxygen concentration or higher, the supply of pump current can be stopped, and the supply of excessive pump current for a long time can be avoided and the oxygen sensor deterioration can be prevented.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the present invention, FIGS. 2 to 7 are diagrams showing an embodiment of the present invention, FIG. 2 is a schematic configuration diagram thereof, and FIG.
Figure 4 is a sectional view of the oxygen sensor, Figure 5 is its block configuration diagram, Figure 6 is a diagram showing the relationship between the air-fuel ratio and detected voltage, and Figure 7 is a diagram showing the relationship between the air-fuel ratio and detected voltage. The figure is a flowchart showing a program for controlling the pump current supply. 1...Engine, 10...Oxygen sensor, 13...Control unit (stop signal generation means), 41...Air-fuel ratio detection circuit (concentration measurement means) ),

Claims (1)

[Claims] A) an oxygen sensor to which a pump current that correlates with the oxygen concentration of the gas to be measured is supplied; and b) an oxygen sensor that detects the oxygen concentration of the gas to be measured based on the value of the pump current supplied to the oxygen sensor. , a concentration measuring means that stops supplying the pump current when a stop signal is input, and c) determines whether or not the atmosphere of the oxygen sensor when the engine is stopped is at a predetermined oxygen concentration or higher; An oxygen concentration measuring device comprising: a stop signal generating means that outputs the stop signal when the above state is reached.