FR2926368A1 - METHOD OF MEASURING THE TEMPERATURE OF A PARTICLE SENSOR TO DETERMINE THE CONCENTRATION IN SWEAT OF THE EXHAUST GAS PIPING OF AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

A method of measuring the temperature of a particle sensor (1) for determining a soot concentration in the exhaust gas duct of an internal combustion engine according to which the particle sensor (1) comprises a sensor (20) on a support layer (10), said sensor having two comb-shaped electrodes (23, 24) interpenetrating to measure the soot concentration, and a heating element (30) for regenerating the particle sensor ( 1) .To measure the temperature by the brief application of an AC voltage, a temperature-dependent impedance is determined for the support layer (10) between the sensor (20) and the sensor heating element (30). of particles (1). During the measurement of the temperature, the supply voltage (47) of the sensor (20) and the supply voltage (48) of the heating element (30) are cut off and during this time the AC voltage is applied.

Description

Field of the invention The present invention relates to a method for measuring the temperature of a particle sensor for determining a soot concentration in the exhaust gas duct of an internal combustion engine according to which the particle sensor comprises a sensor on a support layer, which sensor has two comb-shaped electrodes interpenetrating to measure the soot concentration, and a heating element for regenerating the particle sensor.

STATE OF THE ART To take account of future regulations, it is necessary to monitor the emission of particles from an internal combustion engine, in particular from a diesel engine upstream and / or downstream of its particulate filter during its operation. In addition, it is necessary to establish a prognosis of charge of such a filter for the control of the regeneration, in order to systematically achieve a very strong security and use economical materials. In addition, it is intended to regulate the combustion characteristics of the internal combustion engine based on the information relating to the emission of particles.

To measure the particle concentration in the exhaust gas it is possible to use a resistive particle sensor composed of digiform electrodes which interpenetrate on a ceramic substrate. When particles of carbon black (or soot) settle on the electrode structure, the impedance of the installation changes. In the simplest case, the charge in particles is exploited by an electrical resistance measurement. To better know the probability of particle deposition on the particle sensor, there can be provided a sensor sleeve at the electrode. According to the state of the art, and in one embodiment, a threshold value is set for the resistance or, for a known voltage, the intensity of the current flowing through the particle filter is set and the time between the beginning of a measurement cycle with a particle sensor, not loaded until reaching this threshold value. Once the threshold value is reached, the particle sensor is heated by means of an integrated heating element and the deposited soot particles are removed by burning them; we can then start a new measurement cycle. According to another embodiment, the resistance or intensity signal is determined in a variable or fixed frame of measurement duration and the slope of the resistance signal or the intensity signal is determined. Such a resistive particle detector, operating by accumulation is described in DE 101 33 384 A1. The particle sensor consists of two comb-shaped electrodes which interpenetrate and which are at least partially covered by a sensor sleeve. When the particles of the exhaust gases of an internal combustion engine are deposited on the particle sensor, an exploitable variation of the impedance of the particle sensor is produced, which makes it possible to conclude that the quantity of particles deposited and thus the amount of particles transported by the exhaust gases. The particle sensors have a high transverse sensitivity with respect to other influences such as, for example, the temperature of the sensor, the temperature of the exhaust gases and also the speed of passage of the exhaust gases. These quantities influence both the deposition of the particles on the sensor and the measurement of the impedance of the sensor. Therefore, it is necessary to know particularly the temperature of the particle sensor. Currently, the temperature of the particle sensor is measured by measuring the heating current or using a temperature model recorded in the vehicle engine control. The two methods can also be combined. The disadvantage of this solution is that the temperature of the sensor element is determined only indirectly. The additional temperature sensors would also represent an increase in cost. OBJECT OF THE INVENTION The object of the present invention is therefore to develop a method for measuring the temperature of the sensor element without using additional temperature sensors.

DESCRIPTION AND ADVANTAGES OF THE INVENTION For this purpose, the invention relates to a method of the type defined above, characterized in that for measuring the temperature, by the brief application of an alternating voltage, an impedance dependent on the temperature for the support layer between the sensor and the heating element of the particle sensor. This makes it easy to determine the temperature of the particle sensor without the need for additional temperature sensors. Thus obtained the temperature of the particle sensor can be used for example to correct the transverse sensitivity of the particle sensor and to more accurately determine the concentration of black smoke in the exhaust pipe of the internal combustion engine. The method is useful in the case where the material of the support layer (for example zirconium oxide or YSZ ceramics) becomes more and more conductive as a function of the increase in temperature and thus has a resistance having a NTC characteristic. According to the invention, it is provided that during the measurement of the temperature, the supply voltage of the sensor and that of the supply of the heating element are cut off, and an alternating voltage is applied during this period. This makes it possible to determine the impedance of the support layer without disturbance. This excludes additional currents or voltages that could influence the impedance measurement. If the supply voltage of the sensor and that of the supply of the heating element are cut off for a maximum of 1 s, which corresponds to a sufficiently long measuring time, the sensor element cool significantly. Usually, to determine the impedance, it takes only a measurement time of about 0.5 s. To avoid disturbances related for example to parasitic capacitances, it is advantageous that during the switch-off time of the supply voltage of the sensor and that of the supply of the heating element, the electrodes in the form of combs of the sensor as well as the contacts of the heating conductors of the heating element. To achieve the required temperature measurement in short time intervals, it is advantageous to cut or short-circuit the supply voltage of the sensor and that of the power supply of the heating element or the comb-shaped electrodes. of the sensor and the contacts of the heating conductors of the heating element by means of a semiconductor switch in the form of, for example, a semiconductor relay or a triac. This allows a high switching frequency without wear. In order to measure the temperature, it is advantageous to determine the conductivity of the support layer as a function of temperature using a measuring resistor connected in series with the particle sensor during the measurement. An AC voltage signal applied to the measurement resistor is a measurement of the alternating current through the device and thus a measurement of the conductivity of the support layer depending on the temperature. For a simple operation of the impedance of the AC voltage of the support layer and to determine a maximum value signal, it is intended to rectify the AC voltage signal in the measurement resistor by a rectifier and to smooth the timing of the signal rectified using a capacitance. An additional resistor in series with the rectifier forms with the capacitance an RC element which makes it possible to fix the time constant to smooth the signal. Usually, the frequency of the AC voltage applied for the measurement of the temperature is in a range between 1 kHz and 10 kHz. It is interesting for the insulation resistance and the insulating capacity, between the sensor structure and the carrier layer or between the heating element and the carrier layer, to determine the conductivity using an alternating voltage of which the frequency is greater than or equal to 100 kHz. From this frequency range, the amplitude of the signal of the alternating voltage on the measuring resistor or the amplitude of the rectified signal is independent of the frequency used and the other geometrical conditions being unchanged, this amplitude depends only on the temperature of the carrier layer. Ideally, for the currently customary geometries of particle sensors, it is advantageous to use an AC voltage of the order of 500 kHz. Drawings The present invention will be described in detail below with the aid of an exemplary embodiment shown with the aid of the appended drawings in which: FIG. 1 shows a particle sensor according to the state of the art, FIG. 2 shows a schematic circuit of the external circuit of the particle sensor for measuring the temperature, FIG. 3 shows an equivalent diagram of the temperature measuring device, and FIG. 4 shows a conductivity diagram of the layer. carrier of the particle sensor. DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIG. 1 shows a particle sensor 1 for determining the soot concentration in an exhaust gas duct of an internal combustion engine. The particle sensor 1 comprises a support layer 10, for example ceramic, carrying on one face a heating element 30 whose heating conductor forms a meander. The heating conductor has two contacts 31, 32 for connecting the heating element 30 to a supply voltage 48 (not shown in FIG. 1) to enable the heating or burning of the particle sensor 1 if necessary. 10 may be brought into thermal contact with the above mentioned support layer 10 carrying the heating element 30. This other support layer may be on the same support layer 10 but on its rear face with respect to the element The heater 30 corresponds to the sensor 20 which serves to determine the soot concentration. The sensor 20 is formed by a structure composed of two comb-shaped electrodes 23, 24 which partially interpenetrate while being separated from each other. The comb-shaped electrodes 23, 24 each have a sensor contact 21, 22. These contacts are intended to be connected to the supply voltage 47 of the sensor (also not shown in FIG. 1) or to a measurement unit and control to exploit the sensor signal. In the area of the combs, the two electrodes 23, 24 are at least partly covered by a dielectric 25 so that they can serve as electrodes for a capacitor with a measurable capacitance. The dielectric is itself covered with a protective layer 26 which protects it from the environment to exclude any degradation. The capacity of this sensor device varies according to the deposited soot and this capacity is exploited by the measuring and control unit thus connected. Figure 2 shows schematically the particle sensor 1 connected to an external circuit for measuring the temperature. This diagram corresponds for example to a measurement unit 40. The particle sensor 1 of FIG. 1 has the characteristics already described above. The sensor contacts 21, 22 of the comb-shaped electrodes 23, 24 of the sensor 20 as well as the contacts 31, 32 of the heating element 30 are connected to the measurement unit 40 to be connected by several switches 46 to one another. voltage supply 47 of the sensor or the measuring and control unit for determining the soot content and the voltage supply 48 of the heating element. There is further provided a comb-shaped electrode 23 for the sensor 20 connected to an AC voltage source 41. The other connection of the AC voltage source 41 is connected by a measuring resistor 42 serving as a measurement shunt, connected to the conductor of the heating element 30 in the example presented via the heating conductor contacts 31. The AC circuit is closed by the support layer 10; between the comb-shaped electrodes 23, 24 and the support layer 10 as well as between the heating elements 30 and the support layer, there are insulation resistors 27, 33 not shown as well as insulation capacitors 28 , 34.

According to the invention, it is intended to cut the supply voltage 47 of the sensor 20 and the supply voltage 48 of the heating element 30 during the measurement of the temperature; an alternating voltage is applied during this time. At the same time, it is planned to short-circuit the comb electrodes 23, 24 of the sensor 20 as well as the contacts 31, 32 of the heating element 30 during the cut-off time of the supply voltage 47 of the sensor and the supply voltage 48 of the heating element. This can be done for example by mounting switch 46 as shown in FIG. 2. It is thus possible to use, for example, a relay controlled by a control unit 45 coupled to an operating unit 43 for measuring the temperature and for provide a temperature signal 44. At the same measurement rate, the contacts are switched. In another exemplary embodiment, the supply voltage 47 of the sensor and the supply voltage 48 of the heating element or electrodes 23, 24 of the combs of the sensor 20 as well as the contacts are cut or short-circuited. 31, 32 of the heating element 30 via semiconductor switches. According to the invention, the breaking of the supply voltage 47 of the sensor and the supply voltage 48 of the heating element is only briefly and typically for about 0.5 s. During this time, the AC voltage source 41 is applied so that an alternating current can pass through the measurement resistor 42 as a function of the temperature of the support layer 10.

Fig. 3 shows an equivalent circuit diagram for the alternating current in the temperature measuring device. The AC circuit is composed of the AC voltage source 41 and the measurement resistor 42 on which an AC voltage signal 49 is measured. The amplitude of this signal is proportional to the conductivity of the temperature measuring device. The temperature measuring device is described by the equivalent AC circuit by a series connection consisting of the insulation resistance 27 already mentioned between the electrodes 23, 24 of the combs and the support layer 10 which has a substrate resistance. 11 depending on the temperature and the insulation resistance 33 between the heating element 30 and the support layer 10. In parallel with the insulation resistors 27, 33, the transitions comprise the insulation capacitors 28, 34 already mentioned. . Depending on the usual geometries of the sensor device, there will be, for example, the following characteristic values for the insulation resistors 27, 33 of the insulation capacitors 28, 34 as well as for the substrate resistance 11 which, because of its material ceramic, has a resistance behavior NTC: Surface of the comb-shaped electrodes 23, 24 and surface of the heating conductor: 0.35 cm2 Thickness of the insulation layer: 20 m Thickness of the backing layer 10 (ceramic YSZ) 450 m The following characteristic values are thus obtained:

Insulation resistance R 27,33: 10 MD Insulation capacity C 28,34: 2 nF Substructure resistance Rsub 11 (for example at 350 ° C) 1,7 kSZ, that is within the characteristic range from 1 kSZ

for the relation corresponding to the complex total impedance: zscaptor = 1 / (1 / R + jwC) + Rsub + 1 / (1 / R + jcoC) = 2R / (1 + jcoCR) + Rsub we obtain the values given in as an example above and for a measurement frequency of 500 kHz, a total impedance of amplitude Z sensor = 1049 D. For a measurement resistor 42 of 1 kSZ and an amplitude of the alternating voltage of 1.65 V, for example, an amplitude is obtained for the AC voltage signal 49 on the measurement resistor 42 of the order of 0.81 V. For a maximum value input 50, it is furthermore provided as indicated in broken lines in FIG. 3, to rectify the AC voltage signal 49 on the measurement resistor 42 by means of a rectifier 51, for example of a diode, and to smooth the timing diagram of the rectified signal by means of a capacitor 53 (which is typically 47 nF). An additional resistor 52 (typically 15 kO) is connected in series with the rectifier 51 to form an RC element with the capacitance which sets the time constant of the signal smoothing. A corresponding maximum value signal 54 can be measured on the capacitor 53. FIG. 4 shows a conductivity diagram of the support layer 10 of the particle sensor 1. The substrate conductivity 60 of the support layer 10 is represented as a function of of the frequency 61. The conductivity curve 62 represents the conductivity of the substrate as a function of the frequency for a temperature T1. Another conductivity curve 63 represents the frequency-dependent substrate conductivity for a temperature T2 such that T2> T1. It appears that from a certain frequency, we can exploit the temperature independently of the frequency. For values given by way of example above, this corresponds for example to a frequency greater than about 200 kHz. 25

Claims (4)

1) Method for measuring the temperature of a particle sensor (1) for determining a soot concentration in the exhaust gas duct of an internal combustion engine according to which the particle sensor (1) comprises a sensor (20) on a support layer (10), said sensor having two comb-shaped electrodes (23, 24) interpenetrating to measure the soot concentration, and a heating element (30) for regenerating the sensor of particles (1), characterized in that for measuring the temperature, by briefly applying an alternating voltage, a temperature-dependent impedance is determined for the support layer (10) between the sensor (20) and the heating element (30) of the particle sensor (1). Method according to Claim 1, characterized in that during the measurement of the temperature, the supply voltage (47) of the sensor (20) and the supply voltage (48) of the heating element ( 30) and during this time, the AC voltage is applied. Method according to Claim 1 or 2, characterized in that the supply voltage (47) of the sensor and the supply voltage (48) of the heating element are switched off for a maximum period of 1 s. 4) Method according to claim 1, characterized in that during the cut-off time of the supply voltage (47) of the sensor and the supply voltage (48) of the heating element, the comb-shaped electrodes (23, 24) of the sensor (20) and the heating conductor contacts (31, 32) of the heating element (30) .355 °) Method according to claim 1, characterized in that with the aid of semiconductor switches, the supply voltage (47) of the sensor and the supply voltage (48) of the heating element or the comb-shaped electrodes are cut or short-circuited ( 23, 24) of the sensor (20) and the contacts of the heating conductors (31, 32) of the heating element (30). Process according to Claim 1, characterized in that the conductivity of the support layer (10) is determined as a function of temperature by means of a measuring resistor (42) connected in series with the sensor. of particles (1) during the measurement of the temperature. Method according to claim 1, characterized in that the conductivity of the support layer (10) increases with temperature. Method according to Claim 1, characterized in that the AC voltage signal (49) of the measuring resistor (42) is rectified by a rectifier (51) and the timing diagram of the rectified signal is smoothed by means of a rectifier (51). of a capacity. Method according to Claim 1, characterized in that the conductivity is determined with an AC voltage whose frequency is greater than or equal to 100 kHz.