JPH0627724B2 - Air-fuel ratio detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a device for detecting an air-fuel ratio of a combustion engine in an automobile or the like by using an oxygen sensor.

(Prior Art) Generally, feedback control of an air-fuel ratio in an engine is performed in order to satisfy various requirements such as drivability, fuel efficiency, and exhaust gas countermeasures. In such control, the oxygen concentration in the exhaust gas is taken as a parameter. The air-fuel ratio of the air-fuel mixture is detected.

Therefore, an oxygen sensor capable of detecting the air-fuel ratio in a wide range from rich to lean (for example, JP-A-59-67455).
Japanese Patent Laid-Open No. 59-46350) have been developed.

Such an oxygen sensor focuses on the characteristic that the diffusion limit oxygen amount correlates with the oxygen concentration when the sensor electrodes have a predetermined potential, and by detecting this as a diffusion current (pump current) by an external circuit, The fuel ratio is detected in a wide range. Then, based on such oxygen sensor information, the air-fuel ratio can be feedback-controlled in a wide range from rich to lean.

(Problems to be Solved by the Invention) However, in such a conventional air-fuel ratio detection device, a pump current that correlates with the exhaust oxygen concentration is constantly supplied to the oxygen sensor in the high-temperature exhaust gas, and from this current value, Since the air-fuel ratio is detected, the pump current becomes too large when the air-fuel ratio is operated at the lean limit for a long time or the fuel cut continues for a long time. Durability may be impaired.

Also, the characteristics of the oxygen sensor depend on temperature,
If the exhaust temperature changes rapidly due to a sudden change in operating conditions and the oxygen sensor temperature changes, the deterioration of the platinum electrode or solid electrolyte is likely to be accelerated due to the rapid change of the pump current. Result in less reliable.

In order to prevent such inconvenience, a possible solution is to energize or interrupt the pump current according to the operating conditions or the temperature of the oxygen sensor. However, even under such control, if the oxygen sensor is used in the vicinity of the boundary of the energization / cutoff region of the pump current, the intermittent control of the pump current is frequently performed. In such a case, a large inrush current flows at the start of energization, but since the number of times increases, the durability of the oxygen sensor also deteriorates due to this excessive inrush current.

(Object of the invention) Therefore, the present invention aims to improve the durability of the oxygen sensor by preventing unnecessary pump current from flowing and avoiding the complicated on / off of the pump current, and thereby to improve the air-fuel ratio. The purpose is to increase the reliability of detection.

(Structure of the Invention) An air-fuel ratio detecting device according to the present invention is shown in a first basic conceptual diagram.
As shown in the figure, the oxygen sensor a is supplied with a pump current that correlates with the oxygen concentration in the exhaust gas, and the oxygen sensor is supplied with a pump current when an energization signal is input. The air-fuel ratio detecting means b for detecting the fuel ratio, the operating state detecting means c for detecting the operating state of the engine, the area setting means d for setting the operating area for prohibiting the supply of the pump current, and the operating state of the engine are as described above. When the vehicle is in the operation area, the output of the energization signal is prohibited, and after the operation area is exited, the signal generation means e which outputs the energization signal after a lapse of a predetermined time is provided. And

(Operation) In the present invention, when the operating state at that time is within the preset operating region, the supply of pump current to the oxygen sensor is prohibited, and unnecessary supply of current is avoided.

Further, when leaving the operation region, the supply of the pump current is started with a predetermined time delay, and the complicated on / off of the pump current near the boundary of the operation region is avoided.

(Example) Hereinafter, the present invention will be described with reference to the drawings.

2 to 7 are diagrams showing an embodiment of the present invention, which is an example in which the present invention is applied to an air-fuel ratio detecting device.

First, the configuration will be described.

In FIG. 2, reference numeral 1 denotes 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 Si. The exhaust gas burned in the cylinders is introduced into the catalytic converter 6 through the exhaust pipe 5, and the harmful components (CO, HC, NOx) in the exhaust gas are cleaned in the catalytic converter 6 by the three-way catalyst and then discharged.

The flow rate Qa of the intake air is detected by the air flow meter 7 and controlled by the throttle valve 8 in the intake pipe 3. The opening Cv of the throttle valve 8 is detected by the throttle opening sensor 9, and the rotation speed N of the engine 1 is detected by the crank angle sensor 10.
The temperature Tw of the cooling water flowing through the water jacket is detected by the water temperature sensor 11.

An oxygen sensor 12 is attached to the exhaust pipe 5, and the oxygen sensor 12 is connected to an air-fuel ratio detection circuit (air-fuel ratio detection means) 13. The air-fuel ratio detection circuit 13 supplies a pump current Ip to the oxygen sensor 12, detects the current value, and outputs a voltage signal Vi corresponding to the exhaust oxygen concentration.

The air flow meter 7 and the crank angle sensor 10 constitute an operating condition detecting means 14, and signals from the operating condition detecting means 14 and the respective sensors 9, 11, 13 are input to the control unit 15, which controls the control unit 15 and the control signals. The air-fuel ratio control is performed on the basis of the sensor information of 1. and its detailed configuration will be described later.

3 and 4 are an exploded perspective view and a sectional view of the oxygen sensor 12.

In these figures, 21 is a substrate made of alumina, and an atmosphere introducing plate 24 having an atmosphere introducing portion 23 on a channel is laminated on the substrate 21 via a heater 22. A flat plate-shaped 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 provided on the lower surface of the solid electrolyte 25 on the upper surface corresponding thereto. A sensor cathode (measurement electrode) 27, which is an electrode exposed to exhaust gas, is provided by printing.

Furthermore, on this solid electrolyte 25, a thickness L (L = 0.1 mm
A spacer plate 28 of about 2) is stacked, and a flat plate-shaped second solid electrolyte 29 is stacked thereon. These solid electrolytes 2
5, 29 and the spacer plate 28 cover the sensor cathode 27, and the gas introduction portion (oxygen layer) 30 is provided around the sensor cathode 27.
The oxygen layer defining member 31 for defining the above is configured, and the oxygen layer defining member 31 limits diffusion of oxygen molecules between the exhaust gas and the gas introduction unit 30.

The sensor anode 26, the sensor cathode 27, and the solid electrolyte 25 constitute a sensor section 32, and the sensor section 32 has a voltage (hereinafter, referred to as a sensor) according to an oxygen partial pressure ratio between the atmosphere introducing section 23 and the gas introducing section 30. It outputs Vs (referred to as voltage).

A pump anode 33 and a pump cathode 34 are provided as pump electrodes on the upper and lower surfaces of the second solid electrolyte 29, respectively.
Are provided, and the pump anode 33, the pump cathode 34, and the solid electrolyte 29 constitute a pump section 35. The pump unit 35 controls the oxygen partial pressure of the gas introduction unit 30 according to the value of the pump current Ip supplied between the pump electrodes.

The sensor unit 32, the pump unit 35, the oxygen layer defining member 31, and the atmosphere introduction plate 24 constitute an element unit 36 that detects the oxygen concentration in the exhaust gas. The heater 22 heats the solid electrolytes 25 and 29 to an appropriate temperature to activate them. Also, 41 and 42 are heaters
22 lead wires, 43 to 46 are sensor anode 26, sensor cathode 27, pump anode 33, pump cathode 34, respectively.
Is the lead wire.

FIG. 5 is a circuit diagram showing the configuration of the air-fuel ratio detection circuit 13,
In this figure, the air-fuel ratio detection circuit 13 is composed of a voltage source 49 for generating a target voltage -Va, a differential amplifier 50, a resistor R1, 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 a difference value ΔV {ΔV = Vs − (− Va)}. The current supply circuit 51 flows out (or flows in) the pump current Ip 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, when ΔV is positive, Ip is increased, and when ΔV is negative, Ip is increased.
Reduce. Analog switch 53 is a control unit
When the energization signal Sc is input from 15, the contact is closed to allow passage of the pump current Ip, and when the energization signal Sc is not input, the contact is opened to prevent passage of the pump current Ip. The current supply circuit 52 converts the pump current Ip into a voltage Vi (Vi∝Ip) by the potential difference across the resistor R1 and detects it. 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.

The target voltage -Va is the sensor voltage Vs when the oxygen concentration in the gas introduction portion 30 of the element portion 36 is maintained at a predetermined value, that is, when the oxygen partial pressure ratio between both surfaces of the solid electrolyte 25 becomes a predetermined value. By setting the value equivalent to
The detection voltage Vi proportional to the pump current Ip detected by the current detection circuit 52 uniquely corresponds to the air-fuel ratio as shown in FIG. Therefore, this detection voltage V
By using i, the air-fuel ratio can be continuously and accurately detected over a wide range from the rich region to the lean region.

Referring again to FIG. 2, the control unit 15 has functions as an area setting means and a signal generating means, and the CPU
56, ROM 57, RAM 58 and I / O port 59. The CPU 56 fetches external data required from the I / O port 59 according to the program written in the ROM 57, and also performs arithmetic processing while exchanging data with the RAM 58, and the data processed as necessary. To the I / O port 59. Signals from the sensor groups 7, 9, 11, 13, and 14 are input to the I / O port 59, and the injection signal Si and the energization signal Sc are output from the I / O port 59. The ROM 57 stores the calculation program in the CPU 56, and the RAM 58 stores the data used for the calculation in the form of a map or the like.

Next, the operation will be described.

FIG. 7 is a flowchart showing the pump current control of the program written in the ROM 57, reference numeral P ₁ to P
Reference numeral ₁₀ indicates each step of the flow. This program is executed every predetermined time.

The intake air amount Qa and the rotation speed N are read at P ₁ , and the basic injection amount Tp is calculated at P ₂ according to the following equation.

Tp = K · Qa / N (where K is a constant) In another routine, Tp is feedback-corrected (or open-corrected) based on the output Vi of the air-fuel ratio detection circuit 13 to determine the fuel supply amount, and the injection signal Si is output.

Then, at P ₃ , the current operating state is the pump current I from N and Tp.
It is looked up from the table map shown in FIG. 8 whether it is the energization area of p or the interruption area (corresponding to the operation area where the supply of the pump current Ip is prohibited).

Here, the cutoff area of the pump current Ip in FIG. 8 corresponds to a high load, high rotation area (the area where the temperature of the oxygen sensor 12 rises because the exhaust gas temperature becomes extremely high), and it is accumulated in this area. In this case, Ip is actually cut off, but it is expected that the air-fuel ratio is often switched from feedback control to open control such as acceleration increase, so controllability does not deteriorate.

However, since the pump current Ip is frequently energized and interrupted (ON / OFF) in the vicinity of the boundary of each area, it is necessary to suppress the influence of the inrush current to the sensor. In view of this, in the present embodiment, when Ip is energized, Ip supply is started after a predetermined time has elapsed, and when Ip is cut off, Ip is immediately cut off without a time delay, so that the pump in the vicinity of the boundary between the above areas is pumped. The complicated on / off of the current Ip is avoided and the number of inrush currents is suppressed.

Specifically, first, at P ₄ , it is determined whether or not the current operating state of the engine is within an operating region (pump current Ip cutoff area) in which the supply of the pump current Ip should be prohibited. Since the cutoff area corresponds to a region when the engine operating state is under high load and high rotation where the exhaust state becomes a high temperature state as described above, for example, the basic injection amount T
Area determination can be performed based on _P , the throttle valve opening degree, the intake air amount (these are parameters representing the magnitude of the engine load), and the engine speed N. And
When contained in blocking area (if not in the energizing area other words) ends the current routine immediately stop the output of the energizing signal Sc at P _5. As a result, the supply of the pump current Ip by the air-fuel ratio detection circuit 13 is cut off. Therefore, at high load and high rotation, the oxygen sensor 12
When the temperature is high, the pump current I
By blocking p, deterioration of the electrode and the solid electrolyte can be suppressed.

On the other hand, when it is determined that the energizing area at P ₄ discriminates whether a blocked area in the previous routine at P _6. That is, it is determined whether or not the vehicle has just left the block area. If it was the blocking area last time, the timer is cleared at P ₇ to set its count value CT to CT = 0, and then the timer is incremented at P ₈ to proceed to P ₅ . The timer counts the elapsed time after switching from the interruption area to the energization area.

When switched from the cutoff area energizing area, the first time P ₆ -
P ₇ -P ₈ -P ₅ and flow flows. From the next time onward, the routine proceeds from P ₆ to P ₉ , and at P ₉ , the count value CT of the timer is compared with the predetermined value T ₀ . When CT ≦ T _0, the process proceeds to P ₈ to increment the timer. Therefore, when CT ≦ T _0, the flow flows as P ₆ −P ₉ −P ₈ −P ₅ . Then, when the count value CT of the timer exceeds the predetermined value T ₀ at P ₉ , it is determined that a sufficient time has elapsed from the Ip cutoff state, and the energization signal Sc is output at P ₁₀ . As a result, the supply of the pump current Ip is started again.

In this way, the supply of Ip is not immediately restarted even when the cutoff area is switched to the energization area, and the supply is started after a predetermined time delay. Therefore, even when the oxygen sensor 12 is used in the vicinity of the boundary of energization and interruption of Ip,
Unlike the conventional case, the number of times of rush supply of Ip per unit time is reduced. As a result, it is possible to suppress defects caused by an excessive pump current and improve the durability and reliability of the oxygen sensor 12.

Further, in this embodiment, Ip energization / interruption areas are set to N and Tp.
However, the value of Ip, that is, the air-fuel ratio or the temperature of the oxygen sensor 12 may be added as a parameter, for example. It is possible to directly detect a region where the fuel cut continues for a long time and the air-fuel ratio is operated at the lean limit for a long time, or an operating condition where the sensor temperature suddenly changes to a high temperature state or a low temperature state. It is possible to deal with various driving areas as cut-off areas.

(Effect) According to the present invention, unnecessary pump current is prevented from flowing, and complicated on / off of the pump current is avoided, so that the durability of the oxygen sensor can be improved. The reliability of air-fuel ratio detection can be improved.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, and FIGS. 2 to 8 are diagrams showing an embodiment of an air-fuel ratio detecting device according to the present invention.
FIG. 3 is an overall configuration diagram, FIG. 3 is an exploded perspective view of the oxygen sensor, FIG. 4 is a sectional view of the oxygen sensor, FIG. 5 is a circuit diagram of the air-fuel ratio detection circuit, and FIG. 6 is an air-fuel ratio thereof. FIG. 7 is a flow chart showing a program for controlling the pump current, and FIG. 8 is a diagram showing the energization / interruption areas of the pump current. 1 ... Engine, 12 ... Oxygen sensor, 13 ... Air-fuel ratio detecting circuit (air-fuel ratio detecting means), 14 ... Operating state detecting means, 15 ... Control unit (area setting means, signal generating means).

Claims (1)

[Claims] 1. An oxygen sensor to which a) a pump current correlated with the oxygen concentration in the exhaust gas is supplied, and b) a pump current is supplied to the oxygen sensor when an energization signal is input, and based on the value of this pump current. Air-fuel ratio detecting means for detecting an air-fuel ratio by means of: c) operating state detecting means for detecting an operating state of the engine; d) area setting means for setting an operating area in which the supply of the pump current is prohibited; and e) engine When the operating state of the vehicle is in the operating range, the output of the energizing signal is prohibited, and after leaving the operating range, the signal generating means outputs the energizing signal after a predetermined time has elapsed. An air-fuel ratio detection device characterized in that