JPH0414306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field] The present invention relates to a detection device for measuring or controlling oxygen concentration or air-fuel ratio in exhaust gas of a combustion device such as an internal combustion engine or gas combustion equipment.

[Prior art] Conventionally, an oxygen sensor constructed by coating an oxygen ion conductive solid electrolyte (e.g., stabilized zirconia) with a porous electrode layer (e.g., a porous layer made of platinum) has been used to determine the oxygen partial pressure of exhaust gas. For example, it is possible to control an automobile engine to operate at the stoichiometric air-fuel ratio by detecting the combustion state near the stoichiometric air-fuel ratio based on the change in electromotive force caused by the difference between the oxygen partial pressure and the oxygen partial pressure of the air. generally known.

By the way, the above oxygen sensor can obtain a large change in output when the operating air-fuel ratio (A/F), which is the weight ratio of air and fuel, is around the stoichiometric air-fuel ratio of 14.7, but changes in other operating air-fuel ratio ranges are The output of the oxygen sensor cannot be used when the engine is operated at an air-fuel ratio other than the stoichiometric air-fuel ratio.

In Japanese Patent Application Laid-Open No. 58-153155, two elements each having an electrode layer provided on both sides of the front side of a plate-shaped oxygen ion conductive solid electrolyte are arranged in parallel with a gap between them, and a gap is formed on the front side. proposed an oxygen concentration detection device in which both elements are fixed by providing a has been done. Although such an oxygen concentration detection device has good responsiveness, when operated in a rich fuel region that is lower than the stoichiometric air-fuel ratio number 14.7 corresponding to the output signal, it may have the characteristic of generating an output in the same direction as in a fuel lean region. I understand. In other words, since two air-fuel ratios correspond to the output, there is a problem that air-fuel ratio control can only be applied in cases where it is clear whether the control is in a fuel-rich region or a fuel-lean region. It was hot.

[Object of the Invention] The first object of the present invention is to provide air-fuel ratio detection that can accurately detect the operating air-fuel ratio (A/F) of a combustion device such as an internal combustion engine in the entire range from a fuel-rich region to a fuel-lean region or in any region. A second object of the present invention is to provide an air-fuel ratio detection device that has the advantage of being able to perform accurate and easy feedback control when performing air-fuel ratio feedback control.

[Configuration of the Invention] In order to achieve the above object, the present invention employs the following two configurations.

(First invention) The air-fuel ratio detection device of the first invention includes a solid electrolyte oxygen pump element in which porous electrodes are provided on both sides of an oxygen ion conductive solid electrolyte, and two porous electrodes are provided on both sides of the oxygen ion conductive solid electrolyte. A solid electrolyte oxygen concentration battery element provided with a set of porous electrodes is provided, and the oxygen concentration battery element and an oxygen pump element are disposed opposite to each other via a booth, and the booth communicates with the surrounding gas to be measured. An air chamber communicating with outside air is formed on the side opposite to the booth side of the edge-cut oxygen concentration battery element.

A constant current source is connected to one set of porous electrodes of the oxygen concentration battery element and pumps oxygen from the air chamber to the booth; and a constant current source is connected to the oxygen pump element and is connected to the A variable current source that changes the amount of oxygen pumped out and an electromotive force between the other set of porous electrodes of the oxygen concentration battery element are output, and the variable current source when the output voltage changes rapidly. A configuration including a signal processing section that detects the air-fuel ratio from the current value is adopted.

(Second invention) The air-fuel ratio detection device of the second invention includes a solid electrolyte oxygen pump element in which porous electrodes are provided on both sides of an oxygen ion conductive solid electrolyte, and two porous electrodes on both sides of the oxygen ion conductive solid electrolyte. A solid electrolyte oxygen concentration battery element provided with a set of porous electrodes is provided, and the oxygen concentration battery element and an oxygen pump element are disposed opposite to each other via a booth, and the booth communicates with the surrounding gas to be measured. An air chamber communicating with outside air is formed on the side opposite to the booth side of the oxygen concentration battery element.

The oxygen concentration battery is connected to one set of porous electrodes of the oxygen concentration battery element, and connected to a constant current source and the oxygen pump element for pumping oxygen from the air chamber to the booth. Adopts a configuration that includes a variable current source that maintains the electromotive force of the other set of porous electrodes of the element at a predetermined value, and a signal processing unit that detects the air-fuel ratio from the pump current value supplied to the oxygen pump element. do.

[Effects of the Invention] The air-fuel ratio detection device of the present invention has the following effects due to the above configuration.

The air-fuel ratio (A/F) can be changed over the entire range from the fuel-rich region to the fuel-lean region without switching the voltage or current direction (positive or negative) to the oxygen pump element or the porous electrode of the oxygen concentration cell element. It is possible to obtain the correct detection signal corresponding to the air-fuel ratio,
A detection device is obtained that allows air-fuel ratio control to an arbitrary value.

[Example] Next, the present invention will be explained based on an example shown in the drawings.

1 to 6 show an embodiment of the first invention.

Reference numeral 1 designates an exhaust pipe of an internal combustion engine, which is a fuel system, and 2 designates a detection plug portion of an air-fuel ratio detection device disposed within the exhaust pipe 1. The air-fuel ratio detection plug 2 has a thickness of approximately 0.5mm.
Porous platinum electrode layers 4 and 5, which are porous electrodes with a thickness of approximately 20 μm, are provided on both sides of a flat plate-shaped ion-conducting positive solid electrolyte (e.g., stabilized zirconia) 3 using thick film technology. The porous platinum electrode layers 4 and 5 are coated on both sides of the solid electrolyte oxygen pump element 6 and the flat ion conductive solid electrolyte 7 similar to the oxygen pump element 6 using the thick film technique as in the porous platinum electrode layers 4 and 5. The oxygen concentration battery element 1 includes a solid electrolyte oxygen concentration battery element 12 configured with two sets of porous platinum electrode layers 8, 9 and 10, 11.
One set of porous platinum electrode layers 8 and 9 provided in 2 are provided on both sides of the central part of the ion conductive solid electrolyte 7, and another set of porous platinum electrode layers 1
0 and 11 are provided with a gap so as not to contact the outer peripheral portions of the porous platinum electrode layers 8 and 9. The oxygen pump element 6 and the oxygen concentration battery element 12
In order to form a small gap a with a spacing of about 0.1 mm or less and to dispose them facing each other inside the exhaust pipe 1, the foot portions are connected with a heat-resistant and insulating spacer 13 (filling adhesive may be used). fixed to each other. On the other side of the oxygen concentration battery element 12, a chamber wall 14 is provided to form an air chamber b made of a heat-resistant and airtight material such as metal or ceramic to communicate the porous platinum electrode layers 8 and 10 with the atmosphere. It is being

A support stand 16 having a screw portion 15 is attached to the outer edge of the oxygen pump element 6, the oxygen concentration battery element 12, and the foot portion of the chamber wall 14 by a heat-resistant and insulating adhesive member 17, The support base 1 is attached to the screw part 18 for attaching the detection plug part provided in the exhaust pipe 1.
The air-fuel ratio detection plug part 2 is attached to the exhaust pipe 1 by screwing in the threaded part 15 of 6.

19 is an example of an electronic control device part, and the porous platinum electrode layers 4 and 5 of the oxygen pump element 6 have a small gap a.
The constant current changeover switch 20 is connected to a constant current changeover switch 20, which is a switching means that independently conducts constant currents E1<E2<E3, each having a different value, for pumping oxygen into the exhaust pipe 1. The three current sources V1, V2, and V3 correspond to the current sources E1, E2, and E3.
It is divided into steps, and is electrically connected to V1, constant current source E1, V2, constant current source E2, V3, and constant current source E3, respectively. One set of porous platinum electrode layers 8 and 9 of the oxygen concentration battery element 12 is provided with an output terminal 21 for detecting the electromotive force e generated between the porous platinum electrode layers 8 and 9, and the other set of porous platinum electrode layers 8 and 9 is The porous platinum electrode layers 10 and 11 are connected to a constant current source E4 that pumps oxygen into the small gap a from the air chamber b. It is assumed that the constant current source E2 and the constant current source E4 have substantially the same oxygen pumping capacity and oxygen pumping capacity.

FIGS. 4 to 6 are characteristic diagrams of the air-fuel ratio detection device shown in FIGS. 1, 2, and 3.

A constant current source E1 is applied to the porous platinum electrode layers 4 and 5 of the oxygen pump element 6 of the air-fuel ratio detection unit 2 attached to the exhaust pipe 1 by setting the constant current switch 20 to V1.
When the oxygen pump element 6 is connected, due to the ability of the pair of porous platinum electrode layers 10 and 12 of the oxygen concentration battery element 12 to pump oxygen from the air chamber b into the small gap a.
Since the ability of the porous platinum electrode layers 4 and 5 to pump oxygen into the exhaust pipe 1 is smaller than the small gap a, the porous platinum electrode layers 8, 5 of the oxygen concentration battery element 12 are
Output terminal 2 detects the electromotive force e generated between 9 and 9.
1, the value of the fuel rich region (a') as shown in Figure 4.
A characteristic is obtained in which the electromotive force e rapidly decreases at .
When the constant current changeover switch 20 is set to V2 and the porous platinum electrode layers 4 and 5 of the oxygen pump element 6 are connected to the constant current source E2, the porous platinum electrode layers 10 and 11 of the oxygen concentration battery element 12 are connected to the air. The ability to pump oxygen into the small gap a from the chamber b, and the ability of the porous platinum electrode layers 4 and 5 of the oxygen pump element 6 to pump oxygen from the small gap a to the exhaust pipe 1.
Because the ability to pump oxygen into the body is almost balanced,
At the output terminal 21, as shown in FIG.
A characteristic is obtained in which the electromotive force e rapidly decreases around 14.7. Set constant current selector switch 20 to V3,
When the porous platinum electrode layers 4 and 5 of the oxygen pump element 6 are connected to the constant current source E3, the oxygen concentration battery element 1
Due to the ability of the porous platinum electrode layers 10 and 11 of 2 to pump oxygen into the small gap a from the air chamber b, the porous platinum electrode layers 4 and 5 of the oxygen pump element 6 pump oxygen into the exhaust pipe 1 from the small gap a. Since the ability to pump out the fuel is greater, the output terminal 21 has a characteristic in which the electromotive force e rapidly decreases at the value (c') in the fuel lean region, as shown in FIG.

This embodiment utilizes the characteristics shown in FIGS. 4 to 6.

That is, it utilizes a sudden change in the electromotive force e. For example, when controlling the air-fuel ratio, by setting the constant current selector switch 20 to V1, the characteristics shown in Fig. 4 can be obtained at the output terminal 21, and the air-fuel ratio Taking advantage of the fact that the electromotive force e changes rapidly at a value near ', it is possible to control the engine at a value near the air-fuel ratio a' by setting the constant current selector switch 20 to V1. becomes. Similarly, the engine can be controlled in the vicinity of the stoichiometric air-fuel ratio and in the vicinity of the air-fuel ratio C'.

When controlling the air-fuel ratio of the above engine, the electromotive force e
An arbitrary reference point P point is set between the maximum electromotive force and the minimum electromotive force at the output terminal 21 that detects the
It is arranged to detect when the voltage is higher than the P point and when the voltage is lower than the P point.

In the above embodiment, the air-fuel ratio of the engine was controlled by switching the changeover switch 20 using constant current sources E1, E2, and E3 having a large number of different values. The present invention is not limited to the embodiments, and by using a constant current source whose constant current value can be varied continuously or discontinuously, it is possible to finely control or measure the entire air-fuel ratio range.

FIGS. 7 and 8 show an embodiment of the second invention.

The electromotive force e generated between the porous platinum electrode layers 8 and 9 of the oxygen concentration battery element 12 is applied to the inverting input terminal of the operational amplifier A via the resistor R1, and is applied to the non-inverting input terminal of the operational amplifier A. A pump current Ip is caused to flow between the porous platinum electrode layers 4 and 5 of the oxygen pump element 6 by driving the transistor Tr with the output of the operational amplifier A that is proportional to the difference between the reference voltage Vr and the electromotive force e. It has the ability to control. In other words, the electromotive force e is set to a constant value Vr
It functions to supply the above-mentioned pump current Ip necessary to maintain the current. Further, a resistor R0 is provided to obtain an output signal corresponding to the pump current Ip supplied from the DC power source B to the output terminal 22. Further, a constant current source E6 is connected between the porous platinum electrode layers 10 and 11 of the oxygen concentration battery element 12 to pump a constant amount of oxygen into the small gap a from the air chamber b. C is a capacitor.

FIG. 8 is a characteristic diagram of the air-fuel ratio detection device shown in FIG. 7 above.

In Fig. 8, the reference voltage Vr is set to a constant voltage and the electromotive force e is kept constant (e>0), and the pump current Ip generated between the porous platinum electrode layers 4 and 5 of the oxygen pump element 6 is theoretically It gradually increases as the air-fuel ratio increases from an air-fuel ratio range (fuel rich range) smaller than the fuel ratio 14.7 to an air-fuel ratio range larger than the stoichiometric air-fuel ratio 14.7 (fuel lean range). Another embodiment utilizes the characteristics shown in FIG.

That is, by detecting at the output terminal 22 an air-fuel ratio output signal corresponding to the pump current Ip of the oxygen pump element 6 as shown in FIG. This makes it possible to measure accurately and control the air-fuel ratio at any value.

The shape of the air-fuel ratio detection plug part 2 of the present invention is not limited to the above structure, but can be modified in various ways. That is, in the detection plug part 2 of the above embodiment, although the oxygen pump element 6 and the oxygen concentration battery element 12 are disposed facing each other with the small gap a interposed therebetween, the detection plug part 2 is provided only at the foot portions of the oxygen pump element 6 and the oxygen concentration battery element 12. A spacer 13 is provided to fix the oxygen pump element 6 and the oxygen concentration battery element 12 to each other, and the small gap is communicated with the surrounding gas to be measured through open holes spanning three directions, thereby achieving excellent response. However, the structure is not limited to such a structure, and as long as a small gap is maintained between the elements and reduction in response is not a practical problem, for example, the spacer 13 may also be placed on the edge of the front side of the element. The small hole formed by the spacer 13, the oxygen pump element 6, and the oxygen concentration battery element 12 allows the small gap a to communicate with the surrounding gas to be measured. It can also be configured to
Furthermore, the holes may be replaced with communicating holes in the porous material.

Further, in the above embodiment, two sets of porous platinum electrode layers 8, 9 and 10 provided in the oxygen concentration battery element 12,
No. 11 shows the case where each is provided separately from the others, but only the porous platinum electrode layer (for example, 9 and 11) on one side of the oxygen concentration battery element is provided separately, and the porous platinum electrode layer (for example, 9 and 11) on the other side is provided separately. A porous platinum electrode layer (8 and 10) can also be provided as a common electrode.

In addition, the porous platinum electrode layer 4 of the oxygen pump element 6,
5 and one set of porous platinum electrode layers 8 and 9 of the oxygen concentration battery element 12 and another set of porous platinum electrode layers 1
The electronic control unit 19, including the pumping and pumping directions of oxygen 0 and 11, current switching means, air-fuel ratio detection means, etc., is not limited to the above structure, but can be set in various ways.

The present invention utilizes the various characteristics of the air-fuel ratio detecting device having the above-mentioned structure, either singly or in combination, to measure or feedback control the operating air-fuel ratio over the entire operating range.

[Brief explanation of drawings]

1 to 6 show an embodiment of the first invention, in which FIG. 1 is a configuration diagram of an air-fuel ratio detection device, and FIG.
The figure is a cross-sectional view taken along the - line in Figure 1, Figure 3 is a cross-sectional view taken along the - line in Figure 2, and Figures 4 to 6 are views of one porous platinum electrode layer of the oxygen concentration battery element. A characteristic diagram of an example showing the change in the electromotive force e of the other porous platinum electrode layer of the oxygen concentration battery element with respect to the air-fuel ratio when the input current is kept constant and the value of the constant pumping current of the oxygen pump element is changed; 7 and 8 show an embodiment of the second invention, and FIG.
The figure shows the configuration of the air-fuel ratio detection device. Figure 8 shows the electromotive force e of the other porous platinum electrode layer of the oxygen concentration battery element when the pumping current of one porous platinum electrode layer of the oxygen concentration battery element is kept constant. FIG. 3 is a characteristic diagram of an embodiment showing a change in the pumping current Ip of the oxygen pump element with respect to the air-fuel ratio when the pumping current Ip is constant. In the figure, 1...Exhaust pipe, 6...Solid electrolyte oxygen pump element, 12...Solid electrolyte oxygen concentration battery element, a...Small gap, b...Air chamber.

Claims (1)

[Scope of Claims] 1. A solid electrolyte oxygen pump element having porous electrodes on both sides of an oxygen ion conductive solid electrolyte, and 2 porous electrodes on both sides of the oxygen ion conductive solid electrolyte.
A solid electrolyte oxygen concentration battery element provided with a set of porous electrodes is provided, and the oxygen concentration battery element and an oxygen pump element are disposed opposite to each other via a booth, and the booth communicates with the surrounding gas to be measured. So,
An air chamber communicating with the outside air is formed on the side opposite to the booth of the oxygen concentration battery element, and is connected to one set of porous electrodes of the oxygen concentration battery element, and is connected to the oxygen concentration battery element from the air chamber to the booth. a constant current source for pumping oxygen; a variable current source connected to the oxygen pump element to vary the amount of oxygen pumped from the booth; and the other set of porous electrodes of the oxygen concentration battery element. an air-fuel ratio detection device, comprising: a signal processing section that outputs an electromotive force of , and detects an air-fuel ratio from a current value of the fluctuating current source when the output voltage changes rapidly. 2. A solid electrolyte oxygen pump element with porous electrodes provided on both sides of an oxygen ion conductive solid electrolyte, and 2 porous electrodes provided on both sides of the oxygen ion conductive solid electrolyte.
A solid electrolyte oxygen concentration battery element provided with a set of porous electrodes is provided, and the oxygen concentration battery element and an oxygen pump element are disposed opposite to each other via a booth, and the booth communicates with the surrounding gas to be measured. So,
An air chamber communicating with the outside air is formed on the side opposite to the booth of the oxygen concentration battery element, and is connected to one set of porous electrodes of the oxygen concentration battery element, and is connected to the oxygen concentration battery element from the air chamber to the booth. a constant current source for pumping oxygen; a variable current source connected to the oxygen pump element to maintain the electromotive force of the other set of porous electrodes of the oxygen concentration battery element at a predetermined value; An air-fuel ratio detection device comprising a signal processing section that detects an air-fuel ratio from a supplied pump current value.