JPS5965249A - Oxygen concentration detector - Google Patents

Abstract

PURPOSE:To perform the detection of oxygen concn. with high accuracy even in a lean region, by a method wherein predetermined voltage is applied to an oxygen ion conductive electrolyte and not only a current flowed into the electrolyte but also a current flowed out from the electrolyte are detected. CONSTITUTION:A constant-voltage source 100 applies constant-voltage to a detector 3 and the current thereof is detected by resistance 108 to be outputted to a memory apparatus 51 while converted to voltage by a voltage converter 109. When an air-fuel ratio becomes smaller than a theoretical air-fuel ratio, a current flowing through the resistance 108 is reversely directed to be flowed to earth from resistance 114 and a negative signal is generated in the voltage converter 109. Therefore, the voltage of the constant-voltage source 100 and the electromotive force of a detector 103 are taken and the air-fuel ratio and the output of an adder 111 are made linearily approximate by a function generator 112 while the base current of a transistor 113 is changed on the basis of the output thereof and the current flowing through the resistance 108 is divided to convert the output of the voltage converter 109 to a negative signal in a region smaller than the theoretical air-fuel ratio. By this method, the detection of oxygen concn. with high accuracy is performed.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to an oxygen concentration detector.

[Prior art]

A conventional oxygen concentration detector will be explained below with reference to FIGS. 1 to 4.

In FIG. 1, a combustor 1 is, for example, a gasoline engine or a diesel engine. An exhaust pipe 2 is connected to the outlet of the combustor 1, and a detector 3 is attached to a part of the exhaust pipe 2. Part of the detector 3 consists of a solid electrolyte 31 with oxygen ion conductivity, such as a mixture of Zr0t YvOl. The electrolyte 31 has porous platinum electrodes 3 on both sides thereof.
2.33 is provided. A cover 34 made of a heat-resistant material is attached around the cap 31 to prevent the electrodes 33 of the electrolyte 31 from being directly exposed to exhaust air. An orifice 3 which is a diffusion resistor is formed in a part of the cover 34.
5 is provided. The diameter of orifice 35 is 0.5m+
n, the length is about 2M, and the electrical resistance of the remission substance 31 is from several Ω to several tens of Ω. The volume of the chamber 36 surrounded by the cover 34 and the electrolyte 31 is approximately 4×10−”cn?.

A heater 38 is provided in a part of the detector 3. The heater 38 is made of insulating ceramic, such as silicon nitride, and has a tungsten wire embedded therein. The tungsten wire is powered by an electrical circuit 6. The electric circuit 6 includes a comparator 63, a switch 64, a switch 65, and a power source 66. Heat from the heater 38 is transmitted to the electrolyte 31 and oil 34. A garbage guard 37 is installed around the cover 34,
An orifice 39 is opened in a part of it. Further, the chamber 4o surrounded by the trash can 37 and the cover 34 is communicated with the atmosphere via a pipe 41 and a solenoid valve 42. The electrode 32 is connected to the electric circuit 5 via a terminal 43. The electrode 33 is connected to the electric circuit 5 via a cover 34 f1. 'A rewritable e-storage device 51 is provided as a part of the electric circuit 5. A hollow hole 44 is provided in the terminal 43, and the electrode 32 communicates with the atmosphere.

The operation of the following configuration is as follows. Now, when the switch 65 is closed, current flows through the heater 38. Heater 3
The resistance of the heater 38 is compared with a reference value by the comparator 63 so that the temperature becomes constant within the range of 600 to 1000 tll', and the switch 64 is turned on and off. The electrolyte 31 and the cover 34 are heated by the heater 38, and the oxygen ion conductivity of the electrolyte 31 is improved. Here, the positive electrode 32,
When the electrode 33 is made negative and a voltage of about 0 to 2 V is applied, a current flows through the electrolyte 31 until the oxygen partial pressure in the chamber 36 becomes close to zero. As shown in FIG.
It flows until it balances with the amount of diffused oxygen due to the oxygen partial pressure inside. In addition to the oxygen partial pressure, the amount of diffused oxygen is influenced by the diffusion resistance, that is, the diameter and length of the orifice 35, and changes when dust or the like adheres to a part of the orifice 35, resulting in a detection error.

In the configuration shown in FIG. 1, the orifice 35 is not directly exposed to the exhaust gas, and the door guard 37 prevents particles such as carbon and lead in the exhaust gas and unburned components of the fuel from reaching the orifice 35. 34 is cooled by the exhaust airflow and prevented from being overheated. Here, the orifice 35 may be a ceramic porous material as long as it provides diffusion resistance. Further, when the combustor 1 is started, a large amount of unburned matter is contained in the exhaust gas, and it adheres to the surface of the canopy 34 and the electrolyte 31, or clogs the orifice 35. Book .

In the fourth embodiment of the invention, the electromagnetic valve 42 is opened when the combustor 1 is stopped and started, so that the atmosphere is present in the chamber 40, so that it is possible to prevent contamination at the time of starting. Turn on the switch 65, wait for a certain period of time until the heater 38 is heated, and then measure the electric current 0. in this case,
Since chamber 4o is in the atmosphere,
- Old... (1) Here, K: Diffusion resistance P: Oxygen partial pressure (=21%). This step ◎ is temporarily stored in the storage device 51.

Thereafter, when the electromagnetic valve 42 is closed, the oxygen concentration in the chamber 40 becomes the same as that during exhaust, so if the electric current at this time is measured, the oxygen concentration X becomes. In other words, ■■.

By correcting with , it is possible to eliminate errors caused by changes in diffused resistance.

In Figure 3, there is an electromotive force of 0.5V at the theoretical constant fuel ratio (14,7), and when the air-fuel ratio becomes smaller than that, the electromotive force increases rapidly, and when it becomes 14.5 or less, the electromotive force gradually decreases. Speak.

FIG. 4 shows the relationship between air-fuel ratio and starting force. Here, in automobiles and the like, the oxygen concentration in the exhaust gas fluctuates over time, so the output of the detector is taken as the average of this temporal fluctuation. On the other hand, as shown in FIG. 4, the output of the detector increases in proportion to the concentration when it is 0% or more, and is always zero when it is below 0%. Therefore, when the oxygen concentration fluctuates as shown in the figure, the output of the detector shows the average value V, and in a case like B in the figure, the output of the detector shows V h k. , it will show the error amount with respect to the original output of zero. Since this phenomenon occurs in a low oxygen concentration state, there is a problem in that detection in a lean state cannot be performed with high accuracy.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a ferroconcentration detector fr with high detection accuracy even in a lean region.

[Summary of the invention]

The present invention detects not only the current flowing into the electrolyte but also the current flowing out from the electrolyte.

[Embodiments of the invention]

An embodiment of the present invention will be described using FIGS. 5 and 6.

Constant voltage source 100 generates a constant voltage and applies it to detector 3. The current at this time is detected by the resistor 108, converted to a voltage by the voltage converter 109, and outputted to the storage device 51. The constant voltage source 100 detects voltage by a resistor 106,
According to the reference voltage of diode 105, υ, transistor 0
Controls the base voltage IAL of 4. When the load on the constant voltage source 100 becomes smaller, the base current of the transistor 04 increases, and the m-resistor 102 prevents the base current of the transistor 01 from increasing in the multi-output voltage. The diode Δ-de 107 prevents the electromotive force of the detector from flowing back to the constant voltage source 100 when the voltage applied to the constant voltage source 100 becomes larger than the voltage applied to the constant voltage source 100. For example, by detecting using a buffer amplifier or the like, the electromotive force of the detector 3 can be
A similar effect can be obtained as long as the applied voltage is greater than 0 and does not flow back to the constant voltage source 100. When the stoichiometric air-fuel ratio becomes smaller, an electromotive force as shown in FIG. 4 is generated in the detector 3. Therefore, a new signal detector 120 is used here. Then, the current flowing through the resistor 108 goes in the opposite direction and flows through the resistor 114 to the shearth. Therefore, a negative signal is generated in voltage converter 109. Here, the difference between the voltage of the constant voltage source 100 and the electromotive force of the detector 3 is taken, and the air-fuel ratio is determined by a known function generator 112 and an adder 111
By linearly approximating the output of
By dividing the entire current flowing through the adder 109, a region smaller than the total stoichiometric air-fuel ratio outputted by the adder 109 is outputted as a negative signal, thereby widening the detection region of the detector 3.

FIG. 6 is a characteristic diagram of the embodiment shown in FIG. According to this, when the air-fuel ratio is lower than the stoichiometric air-fuel ratio, it is output as a negative signal.

FIG. 7 is a modification of FIG. 5. Connect the emitter of the transistor 113 to the ground side of the resistor 114, and connect the collector to the resistor 1.
I gave it a 15. Further, the output of the setting device 117 and the detected voltage on the electric circuit side of the resistor 108 are added by the adder 116, and the voltage detector 109 adds the signal and the detected voltage on the detector 3 side of the resistor 108, thereby increasing the voltage. If the air-fuel ratio is set on the larger side, even a region smaller than the stoichiometric air-fuel ratio can be detected as a positive signal.

Figure 8 shows its characteristics.

Although the function generator 112 is used in the embodiments shown in FIGS. 5 and 7, it is also possible to remove the function generator 112 by utilizing the characteristics of the transistor 113, although the linearity will decrease.

FIG. 9 shows another embodiment of the present invention. When the voltage of the detector 3 becomes larger than the applied voltage of the constant voltage source 100, the resistor 1
A reverse current flows through the resistor 108i through the voltage detector 10
The output of 9 becomes a negative output. As shown by the solid line in FIG. 10, below the stoichiometric air-fuel ratio, the air-fuel ratio suddenly drops to nine waves. In Figure 10, the current engine exhaust oxygen level (air-fuel ratio)
When changes temporally and spatially, oxygen ′a changes as shown by the dotted line.
If the air-fuel ratio changes by 2% (about 1 in air-fuel ratio), the output will decrease at the stoichiometric air-fuel ratio. When the oxygen concentration changes by 4% as shown by the dotted line, the stoichiometric air-fuel ratio becomes higher. However, the amount of change is the small expression <
, can also be measured using this method. Also, with this method, the seventh
By applying a bias as shown in the figure, it is possible to detect only the output in the positive direction.

Conventionally, engine air-fuel ratio control was performed using these devices, but the function of the fuel-fuel ratio sensor was to detect, for example, the stoichiometric air-fuel ratio or an air-fuel ratio that was greater than the stoichiometric air-fuel ratio. Therefore, the control device was uncertain. However, in terms of fuel efficiency, it is advantageous for automobile engines to operate at a high air-fuel ratio during partial load.

On the other hand, during acceleration and the like where the engine output is a problem, the air-fuel ratio needs to be set to the output nitrous-fuel ratio (already about 13). Therefore, the air-fuel ratio is in the small region (near 13)' than in the large region (near 20)! It is necessary to freely control it with l:. On the other hand, if the air-fuel ratio is changed rapidly, there is a problem in terms of drivability if the air-fuel ratio is changed stepwise, so the air-fuel ratio needs to be changed smoothly. For this reason, a sensor that can measure air-fuel ratios ranging from 13 to 920 or more as shown in the present invention is required. In particular, when the air-fuel ratio is close to 13, output is produced but fuel efficiency decreases, so if control is controlled by the fuel supply system and air volume, etc., as is currently the case, a slight deviation in the air-fuel ratio may result in increased fuel efficiency, insufficient output, etc. Therefore, control of the output air-fuel ratio will also become important in the air-fuel ratio control of future engines, where output and fuel efficiency will become increasingly strict. On the other hand, when lean burn is performed, HC tends to increase even in a region where the air-fuel ratio is high due to an increase in fincheria in the combustion chamber. Additionally, CO also increases due to the reaction between excess oxygen and HC. Even in this Meljumpan engine, there is no significant difference in the purification performance of Co and HC, so if the air-fuel ratio deviates to a lower value when the output air-fuel ratio is set, the emissions of Co and HC will increase rapidly, resulting in a decrease in fuel efficiency. Therefore, controlling the output air-fuel ratio as well as exhaust gas purification and fuel consumption are important. On the other hand, in terms of NOx purification performance, it is necessary to operate at an air-fuel ratio of around 25.

〔Effect of the invention〕

According to the present invention, the detection M degree in the lean region of the oxygen concentration detector is improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional example, FIGS. 2 to 4 are explanatory diagrams of the example shown in FIG. 1, and FIG. 5 is a configuration diagram of an embodiment of the present invention. , FIG. 6 is the characteristic diagram of FIG.
, FIG. 7 is a configuration diagram of another embodiment of the present invention, and FIG.
The figure is a characteristic diagram of FIG. 7, p1100 is a configuration diagram of another embodiment of the present invention, and p1 FIG. 10 is a characteristic diagram of FIG. 9. 3... Potential detector, 100... Constant voltage source, 108, 11
4 蓼 10 ￥3 [21 躬 4 圀 5th rnQ 00 people 60 O ' 02 (''/,) th '7 (2)

Claims (1)

[Claims] 1. One side of the oxygen ion conductive electrolyte faces the atmosphere, the other side faces a reference chamber with diffusion resistance, a predetermined voltage is applied between both sides, and the oxygen concentration is detected by the current flowing through this electrolyte. An oxygen concentration detector characterized in that when the electromotive force of the electrolyte is greater than the applied voltage, a current flowing from the electrolyte is detected.