JPH0548127Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[0001]

[Field of Industrial Application] This invention relates to a device that detects the air-fuel ratio by measuring the oxygen concentration in the exhaust gas of an internal combustion engine, etc., and specifically relates to an oxygen pump-type air-fuel ratio device made of an ion-conducting solid electrolyte. This invention relates to improvements to fuel ratio sensors.

[0002]

[Prior Art] Conventionally, an oxygen sensor composed of an ion-conducting solid electrolyte (for example, stabilized zirconia) has been used to measure the electromotive force caused by the difference between the oxygen partial pressure of exhaust gas and the oxygen partial pressure of air. It is well known that, for example, an automobile engine can be controlled to operate at a stoichiometric air-fuel ratio by detecting the combustion state at the stoichiometric air-fuel ratio based on a change in the stoichiometric air-fuel ratio.

[0003] By the way, in the above oxygen sensor, the air-fuel ratio A/F, which is the weight ratio of air and fuel, is the stoichiometric air-fuel ratio.
14.7, a large change in output can be obtained, but in other operating air-fuel ratio ranges there is almost no change in output, so when operating the engine at an air-fuel ratio other than the stoichiometric air-fuel ratio, use the output of the oxygen sensor mentioned above. Can not do it.
Although an oxygen pump type air-fuel ratio sensor has been proposed that eliminates this inconvenience and allows the engine to be operated at any air-fuel ratio, it is not practical because its characteristics change significantly with temperature.

[0004] FIG. 4 is a configuration diagram of a conventional oxygen pump type air-fuel ratio sensor, and FIG. 5 is a sectional view taken along the - line in FIG. 4. In the figure, 1 is an exhaust pipe of an engine, and 2 is an air-fuel ratio sensor disposed inside the exhaust pipe 1. This sensor 2 includes a solid electrolyte oxygen pump 6, which is constructed by providing platinum electrodes 4 and 5 on both sides of a flat, ion-conducting solid electrolyte (stabilized zirconia) 3 with a thickness of about 0.5 mm, and 6, a solid electrolyte oxygen sensor 10 is constructed by providing platinum electrodes 8 and 9 on both sides of a flat ion conductive solid electrolyte 7, respectively, and the oxygen pump 6.
and a support stand 11 for arranging the oxygen sensor 10 facing each other with a minute gap d of about 0.1 mm in between.

[0005] 12 is a control device, and oxygen sensor 1
0 is the electromotive force e generated between electrodes 8 and 9 as resistance R ₁
to the inverting input terminal of operational amplifier A via
The output of the operational amplifier A, which is proportional to the difference between the reference voltage V applied to the non-inverting input terminal of the amplifier A and the electromotive force e, drives the transistor _TR to connect the electrodes 4 and 5 of the oxygen pump 6. It has a function to control the pump battery I _P flowing into the pump. That is, it functions to supply the pump current I _P necessary to maintain the electromotive force e at a predetermined value V.

[0006] It also includes a resistor R _O for obtaining an output signal corresponding to the pump current I _P supplied from the DC power supply B, which is the pump current supply means. This resistor R _O corresponds to the DC power supply B, and a desired resistance value is selected so that the pump current I _P does not flow excessively.
C is a capacitor, which forms an integrator together with the operational amplifier A, and acts to make the electromotive force e match a predetermined value V accurately.

[0007] FIG. 6 shows a characteristic diagram of the conventional oxygen pump type air-fuel ratio sensor configured as described above. In FIG. 6, the solid line indicates the temperature of the air-fuel ratio sensor, for example.
It shows the relationship between the air-fuel ratio and the current of the oxygen pump 6 at 600°C, and the broken line shows the same relationship as above at 800°C, for example. It is thought that such characteristic fluctuations occur because the ionic conductivity changes when the temperature of the ion conductive fixed electrolytes 3 and 7 that constitute the oxygen pump 6 and the oxygen sensor 10 changes.

[0008]

[Problem to be solved by the invention] Experiments have shown that when the temperature of the air-fuel ratio sensor is varied over the temperature range of the engine exhaust, the current of the oxygen pump 6 corresponding to the same air-fuel ratio increases by several tens of percent. and
It cannot be put to practical use as an air-fuel ratio sensor. FIG. 7 shows the air-fuel ratio sensor shown in FIG. 4, and shows characteristics common to various fixed electrolytes. The purpose of this invention is to provide an air-fuel ratio sensor that applies the characteristics shown in FIG. 7 and detects and corrects changes in characteristics due to temperature using the internal resistance of the air-fuel ratio sensor itself.

[0009]

[Means for Solving the Problems] This invention includes a gap for introducing engine exhaust gas, a solid electrolyte oxygen pump for controlling the oxygen partial pressure in this gap,
a solid electrolyte oxygen sensor that generates an electromotive force corresponding to the partial pressure of oxygen in the gap and the partial pressure of oxygen in the exhaust gas outside the gap, and a measuring resistor connected in series to the oxygen pump; and current control means for flowing the pump current of the oxygen pump necessary to maintain the electromotive force generated by the oxygen sensor at a predetermined value,
In the air-fuel ratio sensor that detects the air-fuel ratio of the engine using a signal value corresponding to the pump current of the oxygen pump, the voltage at both terminals of the resistor is measured, and these terminal voltage values and the known resistance of the resistor are calculated. Based on the value, a signal value corresponding to the internal resistance value of the oxygen pump and the pump current of the oxygen pump is calculated, and the signal value corresponding to the pump current of the oxygen pump is corrected according to this internal resistance value. An air-fuel ratio sensor for an engine, characterized in that it is equipped with means.

[0010]

[Operation] In this invention, the voltage across the terminals of the resistors connected in series in the oxygen pump is measured using the above configuration, and the internal resistance value of the oxygen pump and the pump current are determined based on these measured values and the known resistance value of the resistor. The signal value corresponding to the above is calculated and the signal value is corrected by the above internal resistance value, so there is no need for a special device such as a temperature sensor to measure the above internal resistance value, and it also corresponds to the pump current. It is now possible to calculate the internal resistance value using the data obtained when obtaining the signal value, which simplifies the device and enables simultaneous measurement of these values.

[0011]

[Embodiment] An embodiment of this invention will be described below with reference to the drawings. In FIG. 1, 13 is a two-channel A/D converter, 14 is a calculation unit that calculates the pump current ip and the internal resistance re of the oxygen pump 6, and 15 is the pump current corrected by the pump current ip and the internal resistance re. This is a correction unit that calculates ip′. Note that the other components are the same as those in FIG. 4, so their explanation will be omitted.

[0012] Next, the operation of this invention will be explained. The terminal voltages v ₁ and v ₂ of each resistor R _O are given by the following equations. v ₁ = ip·(R _O +re) v ₂ = ip·re where ip is the pump current of the oxygen pump 6, and re is the internal resistance of the oxygen pump 6.

[0013] The terminal voltages v ₁ and v ₂ are converted into digital signals by the A/D converter 13 in order to facilitate calculation processing. Digitized terminal voltage
v ₁ and v ₂ are given to the calculation unit 14. Then, in the calculation section, the following equation is calculated: ip = (v ₁ − v _{2 )} ÷ R _O re = _{v 2} ÷ ip , and the pump current ip of the oxygen pump 6 and the internal The resistance re is calculated, and ip and re are provided to the correction section 15.

[0014] The correction unit 15 corrects the pump current ip using the internal resistance re and outputs it as ip'. This correction method will be explained using FIGS. 2 and 3. Figure 2 shows ip′,
It shows the correlation between each variable of ip and re. This correlation is the correlation between the internal resistance re and the sensor temperature (Figure 7), and the pump current ip that indicates the sensor temperature and air-fuel ratio.
(Fig. 6), and by knowing the internal resistance re at the time of measurement, it is possible to obtain ip', which is the temperature-corrected pump current ip. Therefore, the characteristic ip'=f(ip・re) of FIG. 2 is stored in the correction unit 15 in advance, and the pump current ip and internal resistance re are
It is possible to calculate and output temperature-corrected ip' from .

[0015] Incidentally, there are cases where it is difficult to predefine the functional form ip'=(ip·re), but in that case, correction using map data as shown in FIG. 3 is practical. The map shown in Figure 3 is a well-known map that is often used when configuring a control system using a microprocessor, so it will not be described in detail, but the internal resistance
Corresponding to re ₁ , re ₂ , re ₃ . . ., values ip', which are obtained by rereading the pump current ip to correctly indicate the air-fuel ratio, are indicated.

[0016] Since this notation is tested in advance and created based on actual measurement data, it can be easily created even if the functional form is unknown. The correction method is to store this table in advance in the correction section 15, and search and output temperature-corrected ip' from the values of the pump current ip and internal resistance re.

[0017] Although the notation in FIG. 3 is created using representative points by appropriately dividing ip and re, in reality, the
The actual data ip, re output by 4 is not necessarily the representative point, so for example, use the values of the nearest representative point by rounding, or use the values of the representative points on both sides of the data ip, re. A practical method is to perform interpolation calculations.

[0018]

[Effect of the invention] As explained above, according to this invention, the voltage across the terminals of a resistor connected in series with the oxygen pump is measured, and the oxygen pump is determined based on these measured values and the known resistance value of the resistor. The system is configured to calculate the signal value corresponding to the internal resistance value and pump current, and correct the signal value using the internal resistance value, so there is no need for a special device such as a temperature sensor to measure the internal resistance value. Furthermore, since the internal resistance value can also be calculated using the data used to obtain the signal value corresponding to the pump current, the device is inexpensive and simple, and these measurements can be performed simultaneously, which improves accuracy.

[0019] In addition, when calculating the correction from the signal value corresponding to the pump current of the oxygen pump and the map value whose parameters are the internal resistance, the parameter is set to 2.
It is possible to perform interpolation calculations even when a parameter value is not in the map, which has the effect of improving the accuracy of correction.

[0020] Furthermore, when using the internal electrical resistance value on the oxygen pump side, since the measurement is based on the current value, it is easy to measure the internal resistance by additionally measuring only the terminal voltage of the oxygen pump. It is possible to calculate. Furthermore, the components of the arithmetic unit and correction unit can be processed by a microprocessor, and if the system that controls the air-fuel ratio of the engine is configured with a microprocessor, the functions can be reused. The addition of is almost unnecessary. As described above, this invention has the effect of providing an air-fuel ratio sensor with excellent characteristics without complicating the configuration or increasing cost.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an air-fuel ratio sensor according to this invention.

FIG. 2 is a characteristic diagram of the correction unit.

[Figure 3] The same map.

FIG. 4 is a configuration diagram of a conventional oxygen pump type air-fuel ratio sensor.

FIG. 5 is a sectional view taken along the - line in FIG. 4;

FIG. 6 is a characteristic diagram of the sensor in FIG. 4.

FIG. 7 is a characteristic diagram showing the relationship between temperature and internal resistance.

[Explanation of symbols]

1 Exhaust pipe 6 Oxygen pump 10 Oxygen sensor 12 Control device 12' Control device 13 A/D converter 14 Arithmetic unit 15 Correction section.

Claims (2)

[Scope of utility model registration request] 1. A gap for introducing engine exhaust gas; a solid electrolyte oxygen pump for controlling oxygen partial pressure in the gap; and a solid electrolyte oxygen pump for controlling oxygen partial pressure in the gap and oxygen in the exhaust gas outside the gap. a solid electrolyte oxygen sensor that generates an electromotive force corresponding to the partial pressure; and a measuring resistor connected in series to the oxygen pump, which generates an electromotive force that is necessary to maintain the electromotive force generated by the oxygen sensor at a predetermined value. An air-fuel ratio sensor for an engine, comprising: current control means for flowing a pump current of an oxygen pump; calculation of measuring each terminal voltage of and calculating a signal value corresponding to the internal resistance value of the oxygen pump and the pump current of the oxygen pump based on these terminal voltage values and the known resistance value of the resistor. An air-fuel ratio sensor for an engine, comprising: means for correcting a signal value corresponding to a pump current of the oxygen pump according to the internal resistance value. 2. The correction means calculates a signal value corresponding to the pump current of the oxygen pump using a map value using a signal value corresponding to the pump current of the oxygen pump and a signal value corresponding to the internal resistance value as parameters. The air-fuel ratio sensor for an engine according to claim 1, wherein the air-fuel ratio sensor performs correction.