WO2012006989A1

WO2012006989A1 - Oxygen sensor for exhaust-gas measurement

Info

Publication number: WO2012006989A1
Application number: PCT/DE2011/001166
Authority: WO
Inventors: Engelbert Keseberg; Elmar Tschinkel; Gunther Knox
Original assignee: Maha Maschinenbau Haldenwang Gmbh & Co. Kg
Priority date: 2010-06-25
Filing date: 2011-06-03
Publication date: 2012-01-19
Also published as: DE102010030531A1

Abstract

The invention relates to a measuring instrument and an oxygen sensor for exhaust-gas measurement of motor vehicles in order to allow measurement of the oxygen proportion using a wear-free oxygen sensor. The measuring instrument comprises an oxygen sensor (200) on the basis of a zirconium dioxide sensor element, wherein the oxygen sensor (200) has, on a rear side (205), a socket (204) for supplying voltage to the zirconium dioxide sensor element and for outputting a voltage output signal. The oxygen sensor (200) has, in the measuring instrument on a front side, a securing element in order to secure the sensor in the measuring instrument and for supplying the exhaust gas to be measured to the oxygen sensor, and the oxygen sensor (200) comprises an integrated electric heating element (32) and an integrated sensor control element, wherein the sensor control element converts a current output signal of the zirconium dioxide sensor element into the voltage output signal which is tappable at the socket.

Description

OXYGEN SENSOR FOR EXHAUST MEASUREMENT

The invention relates to a measuring device and an oxygen sensor for measuring the exhaust gas of motor vehicles in order to enable a measurement of the oxygen content with a wear-free oxygen sensor.

Measuring devices for measuring the exhaust gas of motor vehicles are used for testing and diagnosis of vehicle exhaust gases. Due to the increasingly stringent exhaust gas regulations according to, for example, Euro 4 or 5, different exhaust gas measuring devices for motor vehicles are known from the prior art, which are brought via an exhaust gas probe, which is placed in the exhaust pipe of the vehicle to be examined, for example, the proportion of gases CO, CO2 , HC, O2 or NO in the vehicle exhaust gas.

For the oxygen (02) measurement in such exhaust gas measuring devices electrochemical electrolyte-based oxygen sensors are known from the prior art, which have a limited life by wear of the electrolyte or the anode material. The life of such oxygen sensors depends primarily on the material conversion of the anode material. A very dry or very moist ambient air and very moist measuring gases have a very shortening of the service life. In addition, the use of increasingly complex emission control systems in the vehicle leads to increasing proportions of water (H2O) in the exhaust gas, which also has a shortening effect on the service life of these oxygen sensors.

It is therefore an object of the present invention to provide a measuring device for measuring the exhaust gas of motor vehicles, which enables the most wear-free determination of the oxygen concentration in the exhaust gas. It is another object of the present invention to provide a wear-free oxygen sensor having a simplified construction for exhaust gas meters. which is suitable for being able to replace conventional electrochemical-based and electrolyte-operated oxygen sensors by retrofitting in exhaust gas measuring devices known from the prior art. This object is achieved by a measuring device for measuring exhaust gas according to the features of patent claim 1 and by an oxygen sensor according to the features of patent claim 10. The dependent claims relate to advantageous Ausgestattungen of the invention. Zirconia dioxide or zirconium oxide zirconia sensor elements for oxygen concentration measurement are known from the prior art, but require a Operating temperature of several hundred degrees C. However, the sample gas temperature in an exhaust gas meter is far below the operating temperature of the common zirconia sensor elements.

The oxygen sensor according to the invention therefore has an integrated electrical heating element which heats the zirconium dioxide sensor element to the required operating temperature.

Furthermore, the oxygen sensor may comprise an integrated sensor control element, which ensures a constant supply voltage of the zirconia sensor element in order to ensure a high measurement accuracy. Furthermore, the integrated sensor control element may convert a current output signal of the zirconia sensor element into a voltage output signal. This has the advantage that the zirconia oxygen sensor according to the invention outputs an output signal which corresponds to the output signal of an electrolyte-based oxygen sensor. This makes it possible to use conventional exhaust gas measuring devices in which the According to the invention sensor can be installed, the output signal processed without further adjustments are necessary.

The oxygen sensor has a socket on a rear side, via which the voltage output signal can be tapped for further processing in the exhaust gas measuring device. This socket can continue to supply the integrated heating element with a voltage. Furthermore, the zirconium dioxide sensor element can be supplied with a voltage via this socket. Preferably, the socket for power supply and voltage output is a 4-pin socket. More preferably, the socket is a 4-pin JST socket to facilitate the replacement of a worn conventional sensor with the wear-free oxygen sensor of the present invention. The device voltage of the flue gas meter serves as a voltage source. Furthermore, the oxygen sensor in the meter on a side opposite the socket on a fastener to attach the sensor in the meter and to supply the oxygen sensor with the measured exhaust gas. Preferably, the fastener is a M16xl screw thread, which is also used in the standard oxygen sensors for mounting in exhaust gas measuring devices used to replace them without modification by retrofitting can.

By integrating the zirconium dioxide sensor element, the electrical heating element and the control element in one component, ie a sensor housing, a particularly compact design and miniaturization is realized. The sensor housing is preferably dimensioned such that it corresponds to the dimensions of conventional electrochemical oxygen sensors in order to replace them by retrofit can. In order to realize a particularly compact design, the electrical heating element and the control element can be arranged together on a circuit board. Preferably, this board is cast together with the zirconia sensor element in a plastic housing.

Furthermore, the control element can linearly convert the current output signal of the zirconium dioxide sensor element into a voltage signal, wherein, for example, a measured oxygen content in the range from 0% to 21% is output as output voltage in the range from OmV to 13 mV.

Furthermore, the measuring device may comprise an exhaust gas probe, a particle measuring chamber, a water separator and a gas outlet, the arrangement of the aforementioned components being such that a measuring gas enters via the exhaust gas probe, the particle measuring chamber is arranged downstream of the exhaust gas probe, the water separator is arranged downstream of the particle measuring chamber, downstream of the water separator, the oxygen sensor is arranged and the sample gas exits via the gas outlet into the environment.

In summary, an exhaust gas measuring device with a zirconia oxygen sensor is made possible by the present invention, which allows a wear-free oxygen measurement. By integrating a zirconia sensor element together with an electrical heating element and a control in a common sensor housing necessary for the operation of the zirconia sensor element heating and control elements are miniaturized by structurally simple way to the sensor of the invention to the limited space in an exhaust gas meter and the comparatively low temperatures of the sample gas.

Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying schematic drawings. Fig. 1 shows schematically a structure of a measuring device according to the invention with reference to a pneumatic plan according to an embodiment of the present invention;

2A shows by way of example a side view of the oxygen sensor according to an embodiment of the present invention;

Fig. 2B shows by way of example a rear view of the oxygen sensor of Fig. 2A;

Fig. 2C is an exemplary perspective view of the oxygen sensor of Fig. 2A; and

3 shows an electrical circuit diagram of the oxygen sensor according to FIG

Exemplary embodiment of the present invention.

1 schematically shows a construction of a measuring device according to the invention with reference to a pneumatic diagram according to an exemplary embodiment of the present invention. The exemplary exhaust gas measuring device described in Fig. 1 is known from the relevant art, with the difference that instead of a conventional oxygen sensor, a wear-free zirconia-based oxygen sensor 200 was used. The components and tubing of the meter described below are exemplary only and may vary depending on the meter used.

The measuring device comprises an exhaust gas probe 11, which is brought into the exhaust pipe of the vehicle to be examined. The exhaust gas samples taken by the vehicle are conducted via an exhaust gas probe line to a first coarse filter 12 and a second coarse filter 13 in order to filter out coarse contaminants from the exhaust gas. Furthermore, the measuring device has an ambient air inlet 34.

Downstream of the coarse filter 12 and 13, a fine filter 16 is arranged, downstream of this fine filter 16 is a water separator 107 a water separator 17 arranged. By means of the fine filter 16 and the water separator 17, the measurement gas for the IR measurement of interfering impurities and moisture is cleaned. The water separated in the water separator 17 is discharged via a water outlet line 108 via the condensate and gas outlet 33 by means of a water separator pump 24. Downstream of the water separator 17, a sample gas check valve 20 is arranged via a sample gas test line 109 for receiving the sample gas from the water separator 17, which is in connection with a line 117 which is connected to a zero gas valve 19. The sample gas test valve 20 and the zero gas valve 19 are designed as 3/2 normally open valves. About the zero gas valve 19, the sample gas test valve 20, a mixture of ambient air and calibration gas is supplied. The ambient air is drawn in via an ambient air inlet 34 and cleaned by an activated carbon filter 18 before entering the zero gas valve 19. The calibration gas is supplied to the zero gas valve 19 via a calibration gas probe 35. The calibration gas is used to calibrate the IR bench 27.

Downstream of the sample gas test unit 20, a sample gas pump 23 is arranged, which is designed as a double diaphragm pump. By means of the sample gas pump 23, the sample gases are conveyed via an IR measuring line 111 to the IR measuring bank 27.

By means of an infrared measurement, the IR measuring bench can determine the CO, CO2 and HC contents contained in the measurement gas and additionally the λ value (measure for the 02 partial pressure). In order to be able to further determine the O 2 and NO x fractions in the measurement gas, a sensor line 114, an oxygen sensor 200 and an NOx sensor 28 may be arranged in parallel downstream of the IR measurement bench. About the condensate and gas outlet 33, the sample gas exits the meter. Between the sample gas pump 23 and the water separator 17, a pressure sensor element 21 is arranged; a further pressure sensor element 26 is arranged between the sample gas pump 23 and the IR measuring bench 27. These pressure sensor elements measure the air pressure and can also record current and voltage values of the measuring bench 27, for example. From the measured air pressure values of the pressure sensor elements 21 and 26, it can be detected, for example, whether one of the input probes of the measuring device is in the water. In this case, the meter can be turned off to prevent damage to the instrumentation due to water ingress. The sample gas pump 23 is driven by a pump motor disposed between the sample gas pump 23 and the water separator pump 24 and further drives the water separator pump 24.

As illustrated in FIG. 1, the incorporation of the wear-free oxygen sensor of the present invention does not require significant changes in the tubing or design of the exhaust gas meter. The features according to the invention which make this possible are described in the following figures.

FIG. 2A shows, by way of example, a side view of the oxygen sensor 200 or of the sensor housing according to one exemplary embodiment of the present invention. The oxygen sensor 200 has a plastic housing in which the zirconia sensor element, the electric heating element, and the zirconia sensor element control element (all not shown) are potted. The housing may for example also consist of metal. The sensor has on a front side a M16xl screw thread 201, via which the sensor 200 is fastened in the exhaust gas measuring device and via which the sensor 200 is supplied with the exhaust gas to be measured from the exhaust gas probe 11. The diameter of the M16xl screw thread is, for example, in the present embodiment, 21.6 mm. The length of the oxygen sensor is, for example, 33 mm and the diameter of the front side is 30 mm, for example. By means of the M16xl screw thread, the zirconia-based oxygen sensor can be used in exhaust gas units. are used, which previously used electrochemical oxygen sensors, since these are also attached there via a M16xl screw thread. The sensor has a front portion 203, a middle portion 202 and a rear portion 201, which are cylindrically shaped and the diameter decreases from the rear to the front portion.

FIG. 2B shows by way of example a rear view of the oxygen sensor from FIG. 2A. The oxygen sensor 200 has at its rear side 205 a 4-pin JST socket 204, which supplies the sensor with a DC voltage of 5 V at 500 mA and is simultaneously used both as a voltage for the heating element and as a sensor voltage. The shape of the cylinder housing is shown in Fig. 2C again in a perspective view.

3 shows an electrical circuit diagram of the oxygen sensor according to an embodiment of the present invention.

The Sch stungskonfigu ratio n shown in Fig. 3 serves as a control element for the sensor element. The zirconium dioxide sensor element is connected to an integrated circuit 31. The zirconia sensor element is known from the prior art, carried out in a conventional manner and not shown through the circuit 33, a constant voltage source for the zirconia sensor is realized, which rests on pin 3. In the present exemplary embodiment, the zirconia sensor is supplied with a constant sensor voltage of 1.8 V by the circuit 33. A current is generated by the sensor at the pin 4 in accordance with the oxygen content of the exhaust gas. This current output is converted to a voltage signal in which this current to the shunt resistor 35 produces a voltage drop which varies linearly with the oxygen level. The relationship between output voltage and oxygen content of the sample gas is linear, as in the common electrochemical sensors, the output voltage for an oxygen content of 0% to 21% at, for example, 0 to 13 mV.

Oxygen sensors made of zirconium dioxide work as oxygen pump cells. When a voltage is applied to the sensor, it works like a current source whose output current depends on the oxygen concentration. Since this property of oxygen ion conductivity only occurs from an operating temperature of over 400 ° Celsius, it is necessary in contrast to the previously used electrochemical oxygen sensors to heat the sensor. The required operating temperature of about 400 ° C of the zirconium dioxide sensor element is provided via an electrical hitting element 31. The electrical heating element 31 consists of three series-connected resistors to which a continuous heating voltage of 5 V is applied, which is provided by the device voltage of the exhaust gas measuring device via the socket 204. The zirconium dioxide sensor element is thus heated via the heating pins 1 and 2.

Claims

claims

1. A measuring device for the determination of exhaust gas components in the exhaust gas of internal combustion engines, with an oxygen sensor (200), wherein

- The oxygen sensor (200) comprises a zirconia sensor element; the oxygen sensor (200) at a rear side (205) has a socket (204) for supplying voltage to the zirconia sensor element and for outputting a voltage output signal;

the oxygen sensor (200) has a fastening element on a front side for fastening the oxygen sensor (200) in the measuring device and for supplying the oxygen sensor (200) with the exhaust gas to be measured; and

the oxygen sensor (200) comprises an integrated electrical heating element (32) and an integrated sensor control element, wherein the sensor control element converts a current output of the zirconia sensor element into the voltage output signal tapped on the socket.

2. Measuring device according to claim 1, characterized in that the sensor control element ensures a constant supply voltage of the zirconia sensor element.

3. Measuring device according to claim 1 or 2, characterized in that the socket (204) for power supply is a 4-pin socket.

4. Measuring device according to claim 1 or 2, characterized in that the socket (204) for power supply is a 4-pin JST socket.

5. Measuring device according to at least one of claims 1 to 4, characterized in that the fastening means is a M16xl screw thread (201).

6. Measuring device according to at least one of claims 1 to 5, characterized in that the exhaust gas meter via the socket (204) provides a heating voltage for the electric heating element (32) and a sensor voltage.

7. Measuring device according to at least one of claims 1 to 6, characterized in that the electrical heating element (32) and the control element are arranged on a circuit board and are encapsulated together with the zirconia sensor element in a plastic housing.

8. Measuring device according to at least one of claims 1 to 7, characterized in that the control element the current output of

Zirconia sensor element linearly converted into a voltage signal, wherein a measured oxygen content in the range O% to 21% gives an output voltage in the range of O mV to 13 mV.

9. The meter of claim 1, further comprising an exhaust gas probe, a particle measuring chamber, a water separator, and a gas outlet.

wherein the arrangement of the aforementioned components is such that a

Measuring gas on the exhaust gas probe (10) enters, downstream of the exhaust gas probe (10) the particle measuring chamber (15) is arranged downstream of Parti kelmesskammer (15) of the water separator (17), downstream of the water separator (17) of the oxygen sensor (28) is, and the sample gas via the gas outlet (33) exits into the environment.

10. oxygen sensor (200) for the determination of exhaust gas components in the exhaust gas of internal combustion engines, wherein

the oxygen sensor (200) comprises a zirconia sensor element; the oxygen sensor (200) has a socket (204) on a rear side (205) for supplying voltage to the zirconium dioxide sensor element and for outputting a voltage output signal, the oxygen sensor (200) has a fastening element on a front side, for fastening the oxygen sensor (200) in the measuring device and for supplying the oxygen sensor with the exhaust gas to be measured; and the oxygen sensor (200) includes an integrated electrical heating element (32) and an integrated sensor control element, wherein the sensor control element converts a current output of the zirconia sensor element into the voltage output signal tapped on the socket.

11. Oxygen sensor for a measuring device according to at least one of claims 1-9.