DE2834228A1 - OXYGEN SENSOR WITH TEMPERATURE COMPENSATION - Google Patents

Description

283422a

Oxygen sensor with temperature compensation

The invention relates to a device for perceiving the 0 "content in the exhaust gas of a motor vehicle engine. The invention is particularly directed to directed an improved resistance-type sensor, the titanium dioxide and zirconia resistors.

Internal combustion engines, in particular internal combustion engines from Automobiles, produce exhaust gases that include carbon monoxide, nitrogen oxides and non-oxidized Hydrocarbons, i.e. unburned or only partially burned Hydrocarbons. All of these substances contribute to air pollution. To keep the proportion of these substances to a minimum To bring, it is necessary to purify the exhaust gases of the internal combustion engines as much as possible, adding the largest possible proportion these substances are effectively removed from the exhaust gases. That means carbon monoxide and the unburned hydrocarbons so far as possible to their next higher level of oxidation, namely carbon dioxide and water (for the hydrocarbons), and the nitrogen oxide compounds are converted into elemental nitrogen and oxygen should.

The conversion of the harmful components of the exhaust gases into non-toxic ones Ingredients, such as carbon dioxide, nitrogen, and water, can be carried out

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by subjecting the exhaust gases to afterburning, ie exposing them to temperatures above about 600 C in the presence of catalysts. In order to use this method successfully, however, the composition of the exhaust gases must be controlled in such a way that virtually complete conversion of the exhaust gases into the non-toxic compounds is possible. This means that the air-fuel ratio is close to the stoichiometric value. The air coefficient Λ was used as a measure of this stoichiometric value. With a value of A = 1, the air-fuel ratio corresponds to the stoichiometric value. If there is no excess oxygen that exceeds the equilibrium of the various possible reactions, Λ is less than 1. If / \ is greater than 1, there is excess oxygen in the mixture. At a value of A = 1, the gas changes from a reducing to an oxidizing state.

In order to get a value of Λ at about 1, one must be exposed to the exhaust gases Sensors are provided to determine the oxygen content. This sensor is connected to a control device that controls the Controls fuel or air supply and supplies the internal combustion engine with the correct fuel-air mixture, so that the exhaust gases have as low a level of harmful components as possible.

Feelers have already been used to measure the concentration of elemental Oxygen respond and where ion-conducting cell electrodes

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Find application. The principles by which a solid electrolyte sensor works are described in detail in US Reissue Patent Re 28,792 (formerly U.S. Patent 3,400,054). In this patent specification is a Solid electrolyte oxygen sensor described, the if one side Exposed to the exhaust gases and the other side to the ambient air, an electrical signal is generated that is a function of concentration of elemental oxygen. Both sides of the solid electrolyte are at least partially coated with platinum to form electrodes. The electrolyte bB consists of stabilized zirconium dioxide. Another example of such a sensor is found in U.S. Patent 3 978 006.

With another type of sensor, the electrical resistance changes of the sensor with the amount of oxygen present in the gas. Such a sensor is generally referred to as a resistance type sensor, and the operating principles of such a sensor are described in US patent specification 3,555,280. The use of a resistance-type titanium dioxide sensor in an engine exhaust control system is disclosed in US Pat U.S. Patent 3,915,135.

The resistance type (titanium dioxide) oxygen sensor has certain Disadvantage. For example, the titanium dioxide sensor must cover an area from 300 ° C to 900 ° C, but the electrical resistance of the sensor does not change over the entire range in a way that

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the sine demarcation between a lean air-fuel mixture and a rich air-fuel mixture allowed. In particular falls for a lean air-fuel mixture over the range of 300 C 900 C is the DC resistance of a titanium dioxide sensor of 3 χ 10 ohms

4th
to about 2 10 ohms, while the direct current resistance for a rich air-fuel mixture drops over the same range from 3 χ 10 ohms to about 40 ohms. As a result, the resistance characteristics of the sensor overlap for a rich and a lean mixture. It is therefore not possible for temperatures in excess of about 250 C with an unbalanced titanium dioxide sensor to make a determination as to whether the air-fuel ratio is rich or lean. Naturally, this is undesirable because it makes it impossible to control the air-fuel mixture because the titanium dioxide sensor cannot distinguish between a rich air-fuel mixture and a lean air-fuel mixture at temperatures above 250 G.

An example of a Bines gas sensor made of a ceramic material made of titanium dioxide, the one circuit for converting a temperature-dependent input signal into a temperature-independent output signal and for Control of the air-fuel ratio of an automobile engine is described in the aforementioned U.S. Patent No. 3,915,135.

The present invention provides an oxygen sensor available, which is almost not adversely affected by the temperature of the perceived gas.

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The invention relates to an oxygen sensor for determining the acid ■ substance content in the exhaust gas of an internal combustion engine, the following Components include: a first resistor made of titanium dioxide, a second resistor made of stabilized zirconium dioxide, a ceramic Insulator with three passages for three electrical lines and a housing that surrounds at least part of the ceramic insulator is mounted.

The aim of the invention is to provide an improved oxygen sensor from To create resistance type.

Another object of the invention is to provide an oxygen sensor to provide, which shows good operating behavior at temperatures from below 250 ° C to above 850 G.

Another object of the invention is to provide a temperature compensated Oxygen sensor, which is perceived by the temperature of the Gas is not adversely affected.

Finally, it is an object of the invention to provide an oxygen sensor create which has improved performance over known resistance-type oxygen sensors.

In the sensor designed according to the invention, there is a zirconium dioxide resistor as a compensation device use while others

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Sensors such as that in U.S. Patent 3,915, cited above a resistor made of platinum wire (or a heating device) use. The zirconium dioxide resistor used in this sensor has a temperature sensitivity similar to that of a titanium dioxide resistor is very similar, i.e. an exponential drop in resistance as a function of increasing temperature. The platinum wire resistance of the In contrast, the above-mentioned patent has an insare sensitivity (i.e. the change in resistance of the platinum wire is directly proportional to the change in temperature) and therefore limits the temperature range, over which the sensor can be operated. As a result, the resistance of a titanium dioxide resistor increases with the change If the temperature changes to such a large extent (non-linear), the use of a linear resistor naturally leads to temperature compensation to a sensor that only works over a very small temperature range. On the other hand, the exponential (nonlinear) Temperature characteristics of the zirconia element of this sensor one excellent temperature compensation from below 250 C to above B50 ° C.

In the following, the invention is illustrated in FIG Connection described with the accompanying drawing. Show it:

1 shows a section through an oxygen sensor designed according to the invention;

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FIG. 2 shows another section through part of the oxygen sensor shown in FIG. 1;

3 is a partial front view of that shown in FIGS Oxygen sensor;

4 is a partial end view of that shown in FIGS Oxygen sensor;

Fig. 5 is a schematic diagram of the in accordance with the invention Method and device according to the invention for measuring the O 2 content in the exhaust gas of an internal combustion engine electrical circuit used; and

Fig. 6 is a diagram in which the voltage across the titanium dioxide resistor is shown as a function of temperature.

In Fig. 1, an oxygen sensor 100 is shown in section. Of the Oxygen sensor 100 comprises a housing 20 in which a ceramic Isolator 10 is attached. The ceramic insulator 10 has a plurality of passages for electrical lines. Through the passage 11, for example, the electrical line 41 from the resistor 101 mounted on the front end to the terminal 70 mounted on the rear end of the insulator 10. The front end of the insulator 10 is provided with a recessed portion 14, in

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dam the resistor 101 is mounted, which consists of a material its resistance varies as a function of temperature and oxygen content of the gas to which it is exposed changes. One such material is titanium dioxide. Lines 41 and 61 extend from the resistor 101 through the ceramic insulator 10 and terminate at terminals 70 at the rear end of the insulator. Each port 70 is cemented in at 40 and at 50 with epoxy resin attached to the ceramic insulator 10, while each electrical line at SO with silver with a terminal 70 is soldered. The housing 20 includes a thread 21 through which the sensors can be screwed with a corresponding thread in the exhaust system of a motor vehicle engine. A notch 17 is at the rear End of the insulator provided as a visual indication of the orientation of the electrical lines.

In FIG. 2, the insulator 10 of the oxygen sensor 100 is in another Section shown. Immediately before the end 15 of the insulator 10 is A resistor 102 is mounted in the recess 14, the resistance of which depends only on the temperature of the gas to which it is exposed is, changes. Lines 51 and 61 coming from resistor 102 extend through passages 12 and 13 to the terminals 70 at the rear of the isolator. The resistor 102 consists of a material like zirconia, which is made up of elements like calcium, Barium, strontium, yttrium, lanthanum, scandium, ytterbium and samarium is stabilized. Zirconia stabilized by calcium and by Yttrium stabilized zirconia are known materials and

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are obtained by adding about 0.05 to 0.3 ^D / o (mol percent) yttrium oxide YO or calcium oxide CaO to zirconium dioxide (ZrO "]. Other materials that can be used instead of zirconium dioxide are yttrium oxide (Y _o 0") , Aluminum oxide (Al “0), cerium oxide (CeO ₀ ), hafnium oxide (HfO ₂ ) and thorium oxide (Th ₀ O).

Fig. 3 is a front view of the sensor shown in Figs. 1 and 2; in which the arrangement of the two resistors 101 and 102, which are called the Exhaust gases from an internal combustion engine are exposed, is shown. The front free end 15 of the insulator 10 surrounds the resistors, so that these are protected against a direct gas flow over their surfaces. The passages 11, 12 and 13 in the ceramic insulator 10 lead Lines 41, 51 and 61 back to the connections at the other end of the sensor, the line 61 being the line that connects to the connection connected between the titanium dioxide resistor and the zirconium dioxide resistor is.

4 is an end view of that shown in FIGS Sensor 100 shown, in which the three connections for receiving and transmitting the voltages to the lines 41, 51 and 61, which in turn for Receiving and transmitting the voltages to the resistors 101 and 102 are shown. The recessed portion 17 on the insulator 10 is used to identify the location of ports 41, 51 and 61.

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In Fig. 5 an electrical circuit is shown, the resistors 101 and 102 of the sensor 100 and at the outputs A and B a display for the O “content of a with the resistors 101 and 102 provides for contacting gas. The circuit generally consists of a battery (12 volts direct current), a voltage regulator Network 103, 104, a voltage divider network 105, 106, the variable resistor

stands 101, 102 of the sensor 100, an isolation amplifier 120 and a Comparator 130 which can provide a digital output. A zener diode 104 builds a maximum voltage level across the fixed resistors 105, 106 and the variable resistors 101, 102. The Zener diode 104 limits the voltage across the resistors 101 and 102 as well as the resistors 105 and 106. With a DC input voltage of 12 volts, this circuit provides a signal greater than 1.5 volts across resistor 101 when the exhaust gas is lean, and a voltage less than 1.5 volts across the resistor 101 if the exhaust gas is rich. Similarly, the resistance values for resistors 103, 105 and 106 are selected, so that the voltage across resistor 106 corresponds to that of pin 7 of the comparator 130 supplied voltage signal corresponds to approximately 1.5 volts. the Voltage across resistor 101 is fed to input pin 6 of comparator 130 via isolating amplifier 120. When the voltage across the resistor 101 is greater than 1.5 volts (the voltage across resistor 106), that is signal applied to comparator 130 on pin 6 is greater than the signal on pin 7 so that the comparator output is zero. When the tension drops to less than 1.5 volts across resistor 101, that's dem

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Comparator 130 at pin 7 applied signal greater than the voltage on pin 6 so that the comparator outputs a digital 12 volt signal. To reverse the phase of the comparator output, only the leads need 7 and 6 can be switched.

Below are typical examples of the level of resistance at different temperatures at the resistors 101 and 102:

For a rich mixture of air and fuel, the resistance at the zirconium

□ 7 ^Dhm
Dioxide resistance 102 at 400 C 3 χ 10 / and at 750 C 6k ohms; for the same air-fuel mixture and the same temperature range, the resistance of the titanium dioxide resistor 101 is 140k ohms and 120 ohmsj, respectively

for a lean air-fuel mixture is the resistance of the Zirkondioxidwiderstandes 102 at 400 ° C for 3 χ 10 ohms and 750 ohms ^D C 6k; and

the resistance of the titanium dioxide resistor 101 for the same mixture

g and the same temperatures is greater than 1 χ 10 ohms and respectively 280k ohm.

It follows that the ratio between the resistance value of the titanium dioxide resistor 101 and the sum of the resistance values of both resistors 101 and 102 at a temperature of 400 ° C to 750 ° C for a rich mixture is quite small (about 0.00467 and 0.0196). At some

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lean air-fuel mixture and a temperature range of 400 C however, up to 750 C the ratio between the resistance value increases of the titanium dioxide resistor 101 and the total resistance value of both resistors 101, 102 compared to the ratio for a rich mixture considerably (around 0.9? and 0.98). As a result, the voltage across the titanium dioxide resistor is significant with a lean air mixture larger than with a rich air mixture.

Fig. 6 shows a diagram in which the voltage across the titanium dioxide resistor is shown as a function of the temperature of the resistor. The temperature of the exhaust gas around the resistor is on the x-axis in degrees Celsius, while the y-axis is that of the titanium dioxide resistance contains measured output voltage when the resistor is in operation with the circuit shown in FIG. The lower curve shows a voltage less than 0.3 volts across the titanium dioxide resistor for temperatures of around 300 C - 800 C and for a rich air-fuel mixture at. The voltage across the titanium dioxide resistor for a lean air-fuel mixture and for the same temperature range is greater than 5 volts. Therefore, when the voltage is above or below a predetermined value, it can be determined from the exhaust gas whether the The air-fuel mixture is rich or lean. For example, if at a reference voltage of 1.5 volts (voltage across resistor 106) diB The voltage across the titanium dioxide resistor 101 is greater than 1.5 volts, the air-fuel mixture is lean, and if the voltage across the titanium dioxide resistor 101 is less than 1.5 volts, the exhaust gas indicates that the engine is receiving a rich air-fuel mixture.

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Since the resistance value of the zirconium dioxide resistor 102 is approximately In the same way as the resistance of the titanium dioxide resistor changes with temperature, that remains between the two resistors divided voltage is essentially the same, unless there is a change in the resistance value of the titanium dioxide resistor as a result of the O ^ content. Since the resistance value of the zirconium dioxide resistor only changes with the temperature to which it is exposed, while the resistance value of the titanium dioxide resistor is more similar Way with the temperature and the CL content changes, the between the two resistors 101 and 102 divided voltage as temperature compensated be viewed so that the voltage across the titanium dioxide resistor 101 provides an indication of the oxygen content of the gas, with the Effect that the influence of temperature has been minimized or completely eliminated.

In operation, the comparator 130 compares the voltage signal across the titanium dioxide resistor 101 (input through input pin 6) with the voltage across resistor 106 (input through input pin 7) and generates output signals when the signal at input 7 is larger and smaller than the signal at input S.

Since the voltage across the titanium dioxide resistor 101 is a function of the oxygen content is in a gas to which the resistor is exposed, the signals at outputs A and B represent a function of the 0 "content in such a gas.

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When a voltage of 12 volts in the circuit shown in FIG is input and the resistors 101 and 102 are used in the exhaust gas of an internal combustion engine, the output of the Circuit at A and B a display of the oxygen content in the exhaust gas, which is used for determining and setting the air-fuel ratio can be used beneficially for such an internal combustion engine.

When the resistors 101 and 102 are exposed to exhaust gas, changes the temperature of the exhaust gas determines the resistance of resistors 101 and 102. However, since both resistors have been selected to be If you have resistance values that change by the same percentage with temperature, the one shared over the two resistance values remains Voltage about the same. However, when the oxygen content of the exhaust gas drops, the resistance value of the titanium dioxide resistor increases 101 from. Consequently, the Op content in the exhaust gas for a rich air-fuel mixture (see Fig. 6) that is introduced into the engine is less than when a lean air-fuel mixture was introduced into the engine will.

Conversely, the voltage on the titanium dioxide resistance increases to one Value greater than 1.5 volts (see Fig. 6) if the titanium dioxide resistance is exposed to an exhaust gas that has a larger proportion of oxygen [lean air-fuel mixture).

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The voltage at the titanium dioxide resistor reaches the input terminal 6 of the comparator 130 via the isolating amplifier 120. The comparator 130 compares this voltage signal with the voltage signal at the resistor 106 (which remains the same). When the voltage on input pin 7 is greater than the voltage on input pin S, comparator 130 outputs a 12 volt signal indicating that less fuel should be added to the air-fuel mixture introduced into the engine. If the voltage on input pin 7 is less than the voltage on input pin S ₁ , comparator 130 outputs a signal (zero volts) indicating that more fuel should be added to the air-fuel mixture introduced into the engine.

Although a preferred embodiment of the invention has been described above has been, the skilled person knows that changes are possible in the invention recited in the preceding claims and that in in some cases certain features of the invention without a corresponding one Use of other features can be used to advantage. For example, the Zener diode 104 does not necessarily have to be installed. In addition, materials other than the proposed titanium dioxide and zirconium dioxide can also be used for the resistors, as long as how the electrical resistance and temperature properties of both materials are substantially the same or differ in change the same ratio and as long as one of the materials has an electrical resistance value, which is also with the 0, -, - content changes in the gas to which the material is exposed.

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Claims (5)

Claims 1. Electrochemical oxygen sensor for determining a given Oxygen content of a gas, characterized in that it comprises the following components: a first electrical Resistance (1O1), the resistance value of which is a function of the temperature of the gas to which it is exposed and the oxygen content of this gas changes, a second electrical resistor (102), the resistance value of which changes only as a function the temperature of the gas to which it is exposed changes, and means to put the first resistor electrically in series with the second resistor to switch. 2. Oxygen sensor according to claim 1, characterized in that it has means (1O, 2O) for mounting the resistors in close proximity having to one another, which comprise three electrical lines (41,51,61) which are electrically insulated from one another, the first line (61) being connected to the connection between the first and the second resistor (101,102) is connected, the second line (41) to the other side of the first resistor (1O1) 9098U / 0649 is connected and the third line (51) to the other Side of the second resistor (1O2) is connected. 3. Oxygen sensor according to claim 2, characterized in that the Means (1O, 2O) for mounting the resistors a ceramic insulator (1O) include, in which three passages (11,12,13) are provided each of which has one of the three electrical lines (41,51,61) contains, as well as a housing (20.) which extends around at least part of the ceramic insulator (1O) is attached. 4. Oxygen sensor according to claim 1, characterized in that the second electrical resistance (102) over a predetermined temperature range of the gas approximately the same resistance-temperature properties has like the first electrical resistance (1O1). 5. Oxygen sensor according to claim 1, characterized in that the first resistor (1O1) consists of titanium dioxide and the second resistor (102) consists of stabilized zirconium dioxide. 909814/0649