DE102009029168B4 - Circuit arrangement for detecting a physical measured variable - Google Patents

Abstract

Circuit arrangement for detecting a physical measurement variable in the exhaust gas of an internal combustion engine with a sensor of a first type or a sensor of a second type, the sensor of the first type or the sensor of the second type having at least one electronic circuit (25; 250) for simulating a sensor of the respective is assigned to another type and the at least one electronic circuit (25, 250) is designed to modify the output signal of the sensor and / or a characteristic curve, characterized in that the sensor of the first type is a broadband lambda probe (20; 200) with a Nernst concentration cell ( 220) and a pump cell (210) and the sensor of the second type is a broadband lambda probe (10) with a single concentration cell (110).

Description

The present invention relates to a circuit arrangement for detecting a physical measured variable, in particular the oxygen concentration, in the exhaust gas of an internal combustion engine, a method for detecting the physical measured variable and a computer program or a computer program product for carrying out the method.

State of the art

In order to ensure optimum combustion in internal combustion engines, such as motor vehicles, the air-fuel ratio in the exhaust gas is determined by the residual oxygen content of the exhaust gas is measured and the fuel metering system, the air-fuel mixture for combustion very accurately to the Value lambda = 1, that is to say a stoichiometric combustion.

For measuring the air-fuel ratio different concentration probes are known, which are used to determine the so-called air ratio - also referred to as lambda. In addition to the known jump probes, it is above all broadband lambda probes which can detect a critical range of the air-fuel ratio.

In the broadband lambda probes, the sensor is designed as a broadband sensor. This is formed by solid electrolyte layers and a number of electrodes, as for example from the German Offenlegungsschrift DE 199 12 102 A1 evident. One part of the electrodes forms in this sensor a so-called oxygen pump cell, another part a so-called concentration cell or Nernstkonzentrationszelle. A pumping voltage is applied to the electrodes of the pumping cell, by means of which a constant oxygen partial pressure, that is also a corresponding air ratio lambda, is set in a first measuring gas space by pumping or pumping oxygen. The pumping voltage is regulated in such a way that a constant voltage value of 450 mV is established at the electrodes of the concentration cell. This voltage corresponds to a value of lambda = 1. Via an electronic control circuit, the pump cell is always supplied with exactly the same amount of oxygen from the exhaust gas that the state lambda = 1 prevails there. In the case of excess air in the exhaust gas, in the so-called lean region, oxygen is accordingly pumped off, whereas oxygen is supplied by reversing the pumping voltage at a low residual oxygen content of the exhaust gas, in the so-called rich region. The respective pumping current Ip, which is proportional to the oxygen or fat gas content in the exhaust gas, forms the output signal of the probe. The evaluation of the pump current values detected by means of the broadband lambda probe takes place on the basis of an Ip lambda characteristic curve.

In addition to the described so-called two-cell principle of a broadband lambda probe with Nernstkonzentrationszelle and oxygen pumping cell (type B) and lambda probes with a single oxygen concentration cell according to the so-called single cell principle (type A) are known. In this case, a Nernstkonzentrationszelle is omitted in addition to the pump cell. Instead of adjusting to a constant lambda value in a measuring gas chamber, broadband probes according to the single-cell principle pump out the diffusing oxygen from the measuring gas space only with a constant pumping voltage. The result is a characteristic that is determined by the oxygen concentration. Broadband probes based on the two-cell principle (type B) and on the single-cell principle (type A) thus differ mainly in their output signals, resulting in different Ip lambda characteristics.

It raises the problem that, for example, in motor vehicles both broadband probes are used according to the two-cell principle as well as the single-cell principle. Due to the underlying different principles interchangeability of the probes is not given, especially with regard to a maintenance or repair of motor vehicles.

The invention therefore has the task of eliminating this disadvantage and to enable interchangeability of broadband probes according to the single cell principle and the two-cell principle and generally a replaceability of different probes or sensors of different types.

Other arrangements are from the JP 2004 093 957 A and the GB 2 320 577 A known.

Disclosure of the invention

Advantages of the invention

This object is achieved by a circuit arrangement for detecting a physical variable in the exhaust gas of an internal combustion engine and by a corresponding method, as described in the independent claims. Preferred embodiments of this circuit arrangement and method are the subject of the dependent claims.

The circuit arrangement according to the invention serves to detect a physical measured variable, in particular a gas component concentration, preferably the oxygen concentration, in the exhaust gas of an internal combustion engine. The capture of Physical measured variable is carried out with a sensor of a first type or with a sensor of a second type, wherein the sensor of the first type or the sensor of the second type is associated with at least one electronic circuit for simulating a sensor of the other type. By means of this electronic circuit, for example when using a sensor of a second type, which is installed in the course of a repair or maintenance of a motor vehicle, it is possible to simulate a sensor of a first type which had originally been installed, so that during repair or maintenance of a motor vehicle Sensor of the first kind can be replaced by the sensor of the second kind, without the engine control unit would have to be replaced or re-fed. The same also applies in the reverse manner, ie when replacing a sensor of a second type by a sensor of a first type, in that in each case the replacement or the new sensor is associated with an electronic circuit in the manner described.

The sensor of the first type as well as of the second type is in each case a broadband lambda probe, namely a broadband lambda probe with a Nernst concentration cell and a pump cell according to the so-called two-cell principle (type B) and the sensor in the first type the second type to a broadband lambda probe with a single concentration cell according to the so-called single cell principle (type A). In addition, the sensor of the first type and the sensor of the second type can also be sensors of one type, for example of the type B or of the type A, which are operated, for example, with different characteristics or different operating and / or signal parameters , By assigning an electronic circuit according to the invention, the various sensors of different types can be exchanged or replaced.

In a preferred embodiment of the circuit arrangement according to the invention, the at least one electronic circuit is used to modify the output signal of the new sensor or the broadband lambda probe and / or to modify a characteristic curve or a pump current lambda characteristic of the new broadband lambda probe, so that the broadband lambda probe to be replaced or whose output signals are simulated. The same can also be used, for example, in the case of nitrogen oxide sensors which are operated with different operating modes or different characteristic curves and can be interchanged by assigning an electronic circuit to one another. Thus, by using an electronic circuit according to the invention, for example when using a type B broadband lambda probe, which is installed in the course of a repair or maintenance of a motor vehicle, it is possible to simulate a type A lambda probe which had originally been installed. As a result, in a repair or maintenance of a motor vehicle, a type A broadband lambda probe can be replaced by a type B broadband lambda probe without the engine or third party engine control unit having to be replaced or re-fed. The same applies in the opposite way, d. H. when replacing a type B probe by a type A probe, preferably by each of the replacing or the new broadband lambda probe is associated with an electronic circuit in the manner described. Similarly, one type of type A or B probe may be replaced by another type of type A or B probe.

The electronic circuit is realized in particular such that the actual output signal of the new sensor, for example the probe voltage of the new lambda probe represents the input signal of the electronic circuit and that the signal modified by the circuit forms the output signal of the new lambda probe during its connection, which is in a control unit is fed so that the output signal of the original probe is simulated.

The electronic circuit can be realized as a circuit or as a program simulating the circuit, for example in a control unit.

In a preferred embodiment of the circuit arrangement according to the invention, a differential voltage between the probe voltage and a predeterminable voltage is first formed. The differential voltage is preferably amplified and then multiplied or converted by a constant factor. This modification of the output signal of the new probe is realized by corresponding circuit elements. As a result, the characteristic curve of the new probe, which reflects the relationship between the voltage and the pumping current of the probe, can be adapted to the corresponding characteristic of the exchanged probe, so that the pumping current of the new probe is in some way "translated" into the pumping current of the exchanged probe , When these somewhat translated values are fed into the exchanged probe control unit, this control unit can correctly convert the values of the new probe. The factor with which the amplified differential voltage is converted depends on the characteristics of the respective characteristic curves. For example, the factor may include a negative sign when the slope of the characteristic of the exchanged probe is opposite to the slope of the new probe.

To realize the circuit arrangement, the circuit arrangement comprises various electronic components, in particular operational amplifiers, transistors and resistors, for example also adjustable or trimmable resistors.

With particular advantage can be made by the electronic circuit to equalize the characteristics of the various probes, a current balance, in particular by appropriately designed resistors. For current balancing, voltage-controlled current sources can also be used.

In a preferred embodiment of the circuit arrangement according to the invention, the electronic circuit is arranged in a plug, on a plug, in a cable harness and / or on a cable harness. You can z. B. may be provided in the universal connector housing of the subsequently inserted sensor. Thus, the sensor to be replaced can be provided together with the electronic circuit according to the invention as a component suitable for replacing a sensor of a different type or of the same type with a different characteristic or other operating and / or signal parameters.

In a further preferred embodiment of the circuit arrangement, the electronic circuit is integrated into the sensor or the probe as such, for example by the electronic circuit being embedded in a probe body in order to be able to operate the probe virtually independently of the respective control device. This embodiment is particularly suitable for those sensors that do not need to be operated at high temperatures.

In a particularly preferred embodiment of the circuit arrangement according to the invention, an electronic circuit is provided which is provided both for modifying the output signal of the sensor and / or the characteristic curve as well as for operating the sensor. In particular, this electronic circuit comprises two parts, wherein the first part is provided for the actual operation of the sensor and the second part causes the modification of the output signal and / or the characteristic curve. These two functions are preferably carried out in a single circuit. In other embodiments, two or more separate circuits are provided.

The circuit arrangement according to the invention is particularly suitable for detecting oxygen concentrations using broadband lambda probes. In other embodiments, the circuit arrangement is also suitable for example for the detection of nitrogen oxides in the exhaust gas of an internal combustion engine by using corresponding nitrogen oxide sensors. In particular, nitrogen oxide sensors with different modes of operation, for example nitrogen oxide sensors according to the reduction principle and nitrogen oxide sensors according to the titration principle, or with different characteristics can be exchanged with one another.

In particular, in the case of broadband lambda probes, the circuit can furthermore be assigned a microprocessor for the regulation of a heating of the probe and / or for a compensation of the static pressure sensitivity difference and possibly also an atmospheric pressure sensor.

The invention further comprises a method for detecting physical measured variables in the exhaust gas of an internal combustion engine with a sensor of a first type or a sensor of a second type. This method is characterized in that a sensor of the other type is simulated by at least one electronic circuit to to allow interchangeability of sensors of different types. For example, hereby the oxygen concentration in the exhaust gas of a broadband probe having either a Nernst concentration cell and a pump cell according to the so-called two-cell principle (type B) or a single concentration cell according to the so-called single cell principle (type A) can be detected. The detection of the oxygen concentration, for example, by means of adjustment with an Ip lambda characteristic. The output signal of the broadband lambda probe and / or the Ip lambda characteristic of the broadband lambda probe is modified by an electronic circuit so that, for example, starting from a type B broadband probe, a type A broadband probe or another probe of the same type can be simulated or vice versa. This inventive method thus enables the interchangeability of type A broadband probes with type B broadband probes and vice versa and of different probes of the same type. As a result, for example, a type A broadband probe already installed in the vehicle can be replaced by a type B broadband probe by assigning the electronic type B broadband probe an electronic circuit which modifies the output signal and / or the characteristic of the wideband probe in such a way that a type A Broadband probe is simulated. In order to simulate the output signal characteristic or the characteristic curve as a function of the pumping current Ip above the gas concentration (rising or falling probe signal) of the respective other sensor, a differential voltage is preferably formed between the output signal of the sensor and a predeterminable voltage. This signal is preferably amplified and reacted with a constant factor. As a result, the characteristic curve or the pumping current of one type be translated into the pumping current of the other type. With regard to further features of the method according to the invention, reference is made to the above description.

Furthermore, the invention comprises a computer program that performs all the steps of the method described, when it runs on a computing device or a controller. Finally, the invention comprises a computer program product with corresponding program code for carrying out the method.

Further features and advantages of the invention will become apparent from the following description of the figures in conjunction with the embodiments. In this case, the various features can be implemented individually or in combination with each other.

Brief description of the figures

In the drawings show:

1 a schematic representation of a broadband lambda probe according to the single-cell principle (type A) with a connected control unit;

2 a schematic representation of a broadband lambda probe according to the two-cell principle (type B) with an associated electronic circuit according to the invention and a connected control unit,

3 (A) the characteristics of a type B probe and a type A probe; 3 (B) an exemplary electronic circuit according to the invention as a block diagram;

4 an exemplary circuit arrangement for the realization of the electronic circuit 3 (B) ;

5 a schematic representation of a broadband lambda probe according to the two-cell principle (type B), which is used as a type A probe, with a further example of an associated electronic circuit according to the invention and a connected control unit and

6 an exemplary electronic circuit for implementing the circuit 5 ,

embodiments

1 schematically shows a broadband lambda probe 10 according to the single-cell principle (type A), which in a conventional manner to a control unit 12 or a control unit is connected. The broadband lambda probe 10 includes a single concentration cell 110 , is pumped via the with a pumping voltage US diffusing oxygen from a sample gas space. A current flow Ip is detected, which represents a measure of the oxygen concentration, which is determined on the basis of an Ip characteristic curve. The pumping current measurement and evaluation takes place in a control unit 12 having a Type A Application Specific Circuit (ASIC) 13 and a microprocessor 14 includes. The broadband probe 10 is with a heater 130 equipped with the battery voltage U_Batt and controlled by an internal resistance measurement Ri.

2 shows in a schematic way as a block diagram, such as a broadband lambda probe according to the single-cell principle, as in 1 is shown by another probe, in particular a broadband lambda probe 20 according to the two-cell principle (type B), is replaced by the output signal UA of the evaluation circuit 22 the broadband lambda probe 20 via an electronic circuit 25 is changed so that that the circuit 25 leaving signal US or the voltage characteristic at the terminals US and US + simulates the output signal of a type A probe and this simulated signal in the control unit 12 a type A probe can be fed. The type B probe 20 comprises an outer pumping electrode APE and an inner pumping electrode IPN, via which a pumping cell 210 is supplied with voltage and so in a measuring gas chamber, a constant composition of the sample gas, namely lambda = 1 (probe voltage = 450 mV), guaranteed. The adjustment of the pumping current Ip is based on a comparison with a reference voltage across the reference electrode RE via the Nernst concentration cell 220 , The required pumping current Ip is evaluated as an output signal. The evaluation takes place in the control unit 22 or evaluation circuit with a type B-specific circuit (ASIC) 23 and a microprocessor 24 the type B probe. About the microprocessor 24 will the heater 230 the probe 20 regulated.

For the evaluation of the probe signal, both in a type A probe and in a type B probe, corresponding Ip lambda characteristics are used as a function of the pump current Ip above the gas concentration. Due to the differing measuring principles, however, the output signals of both types of probes are not interchangeable. According to the invention therefore an electronic circuit 25 provided the Ip lambda characteristic of the type B probe 20 and / or the output signal UA of the probe 20 modified so that the evaluation signal of a type A probe 10 is simulated, making it the type B broadband lambda probe 20 can replace the type A broadband lambda probe without the original control unit 12 , in particular the engine control unit, would have to be replaced or re-fed.

Preferably, the electronic circuit 25 that a separate mass 0 designed such that various types of exchange probes can be operated and that different types of Ip-lambda characteristics are output as an output, the associated parameters can be adjusted by programming the electronic circuit, so that no hardware change of the electronic circuit 25 necessary is. To adapt to different types of probes or sensors, preferably one or more adjustable resistors can be provided.

In a preferred embodiment of the circuit arrangement according to the invention, the electronic circuit 25 executed such that all relevant operating parameters of the probe to be replaced 10 , such as As the internal resistance Ri, are properly simulated, so that of the diagnostic functions in the control unit 12 (Control unit) to which the electronic circuit 25 connected, the replacement probe 20 with electronic circuit 25 is not recognized as faulty and the replacement probe 20 operated with compatible operating parameters.

To compensate for different power requirements of different sensors, it is provided, the connection H- the heater 230 the new probe to the H input of the controller 12 to connect the replaced probe. The heater of the exchanged probe can be simulated by a correspondingly designed resistor corresponding to an internal resistance Ri of the heater, which pre-mirrors a sufficiently high temperature of the sensor, so that the heater 230 of the sensor 20 not from that in the control unit 12 provided heating circuit is controlled.

3 (A) shows on the left side a typical characteristic of a broadband lambda probe according to the two-cell principle (type B), which represents the relationship between the probe signal UA and the gas concentration and the pumping current Ip. To the right is a typical characteristic of a broadband lambda probe according to the single-cell principle (type A). The electronic circuit according to the invention modifies the probe signal UA of a type B probe in such a way that an output signal US of a type A probe is simulated and this output signal from the controller of the type A probe can be evaluated such that the oxygen concentration in the exhaust gas of an internal combustion engine can be detected correctly.

3 (B) shows a block diagram of an example of an electronic circuit for converting the probe signal UA of a type B probe into the output signal US of a type A probe. UA represents the output signal of the evaluation circuit of the new probe. Between the output voltage UA and a predetermined voltage, a difference is formed and via the differential amplifier 31 strengthened. The specifiable voltage of 1.5 V shown in this example is based on the fact that at a voltage of 1.5 V at lambda = 1, the current Ip = 0, as can be seen from the in 3 (A) shown characteristic of the type B probe results. In the following shows 3 (B) the schematic realization of the implementation of the amplified differential voltage with a factor, for example the factor -0.27 for simulating the deviating characteristic of the original type A probe. By voltage-controlled current sources 305 and 306 In this case, the current is controlled in the appropriate direction. By a high-impedance resistor 307 , for example, 1 megohm, a current adjustment is made for the terminal US-, so that a suitable signal US- / US + is provided for the control unit of the exchanged probe.

4 shows an exemplary implementation of the circuit 3 (B) for simulating the probe signal US- / US + of a type A probe, starting from the output voltage UA of the evaluation circuit 22 the type B probe 20 , The gain of the voltage difference between the output signal UA and a predetermined voltage, z. B. 1.5 V, via a differential amplifier, the three operational amplifier 401 . 402 . 403 is formed. The difference signal UAdiff is via a further operational amplifier 404 and through two transistors 405 and 406 depending on rich or lean exhaust gas changed so that the output signal of a type A probe US- / US + or the voltage characteristic of a type A probe is simulated. In order not to disturb the connection US-, this connection is preceded by a high-resistance resistor R3, for example 1 megohm.

The one through the operational amplifier 401 . 402 . 403 Differential amplifier formed amplifies the voltage difference between the input voltage UA and a predetermined voltage by a voltage divider, which is formed from the resistors R6 and R4, in this example 1.5 V. The voltage difference is applied to a second circuit part having two transistors 405 and 406 which basically simulate pumping current sources of a rich pumping current and an opposite lean pumping current. The pump current sources are through the operational amplifier 404 followed by two transistor circuit parts, which are the two transistors 405 and 406 (NPN transistor Q1 and PNP transistor Q2). At the common emitter 407 the voltage controlled current sources 405 and 406 is thus at a current of 0 (lambda = 1), for example, 1.8 V, so that at the output of the two terminals of the probe US and US + a voltage characteristic arises, the voltage characteristic of the replaced sensor 10 equivalent.

5 shows another example of an electronic circuit 250 , which is the output of another type B probe 200 with a pumping cell 210 and a Nernst concentration cell 220 modified so that the output signal of a type A probe passing through the probe 200 is replaced, is simulated. Here is the type B probe 200 in some way as a type A probe, so as a single cell, connected by the outer pumping electrode APE is connected to the air duct. The output signal of this single-celled type B probe 200 gets into the electronic circuit 250 fed. The signal becomes dependent on rich or lean exhaust gas via two power sources 505 and 506 adjusted so that the probe signal US- / US + another type A probe, which is to be replaced, is simulated and in the control unit 12 the other type A probe can be fed. Essentially, the current is reduced and adjusted by a rich and a lean function to the current of the original probe. The advantage here is that in this arrangement, if necessary, can be dispensed with a microprocessor for the new sensor.

6 shows an exemplary structure of the electronic circuit 250 of the 5 with operational amplifiers 601 to 605 and transistors 606 and 607 , In this circuit is compared to the in 4 shown circuit of the transistors upstream and replaced as an integrator operational amplifier replaced by two operational amplifiers.

Claims (9)

Circuit arrangement for detecting a physical variable in the exhaust gas of an internal combustion engine with a sensor of a first type or a sensor of a second type, wherein the sensor of the first type or the sensor of the second type at least one electronic circuit ( 25 ; 250 ) is associated with the simulation of a sensor of the other type and wherein the at least one electronic circuit ( 25 . 250 ) is designed for modifying the output signal of the sensor and / or a characteristic curve, characterized in that the sensor of the first type is a broadband lambda probe ( 20 ; 200 ) with a Nernst concentration cell ( 220 ) and a pump cell ( 210 ) and the sensor of the second type a broadband lambda probe ( 10 ) with a single concentration cell ( 110 ). Circuit arrangement according to claim 1, characterized in that by the modification of the pump current lambda characteristic of a broadband lambda probe ( 20 ; 200 ) with a Nernst concentration cell ( 220 ) and a pump cell ( 210 ) or a broadband lambda probe ( 10 ) with a single concentration cell ( 110 ) either a broadband lambda probe ( 10 ) with a single concentration cell ( 110 ) or a broadband lambda probe ( 20 ; 200 ) with a Nernst concentration cell ( 220 ) and a pump cell ( 210 ) is simulated. Circuit arrangement according to one of claims 1 or 2, characterized in that the modification of the output signal of the sensor and / or the characteristic curve by the formation of a differential voltage between the probe voltage and a predetermined voltage, a gain of the differential voltage and implementation with a constant factor. Circuit arrangement according to one of the preceding claims 1 to 3, characterized in that the modification of the output signal of the sensor and / or the characteristic is carried out by a current balance. Circuit arrangement according to one of the preceding claims, characterized in that the electronic circuit ( 25 ; 250 ) in a plug, on a plug, in a wiring harness and / or on a wiring harness of the sensor ( 20 ; 200 ) is arranged and / or that the electronic circuit is integrated in the sensor. Circuit arrangement according to one of the preceding claims, characterized in that the electronic circuit ( 25 ; 250 ) both for simulating the sensor of the other type ( 10 ) as well as to operate the sensor ( 20 ; 200 ) is trained. Method for detecting a physical measured variable in the exhaust gas of an internal combustion engine having a circuit arrangement according to one of the preceding claims, characterized in that by the at least one electronic circuit ( 25 ; 250 ) the sensor of the other type is simulated, wherein a differential voltage between the probe voltage and a predetermined voltage is formed to simulate the sensor of the other type, the differential voltage is amplified and implemented with a constant factor. Computer program that performs all the steps of a method according to claim 7, when it runs on a computing device or a controller. Computer program product with program code, which is stored on a machine-readable carrier, for performing a method according to Claim 7, when the program is executed on a computer or a control device.

Images