WO2015082197A1

WO2015082197A1 - Control unit for operating a broadband lambda probe

Info

Publication number: WO2015082197A1
Application number: PCT/EP2014/074674
Authority: WO
Inventors: Bernhard Ledermann; Claudius Bevot; Anne-Katrin MITTASCH; Ruediger Fehrmann
Original assignee: Robert Bosch Gmbh
Priority date: 2013-12-04
Filing date: 2014-11-14
Publication date: 2015-06-11
Also published as: DE102013224811A1

Abstract

The invention relates to a control unit for operating a particularly unicellular broadband lambda probe of an exhaust gas aftertreatment system of an internal combustion engine, the broadband lambda probe being maintained in a limiting current operation by means of a pump voltage (303), thereby producing a pump current (304) which is proportional to the remaining oxygen in the exhaust gas, and the pump voltage (303) being adjusted depending on the pump current (304) produced.

Description

Description title

Control unit for operating a broadband lambda probe

The invention relates to a control unit for operating in particular a single-cell broadband lambda probe of an internal combustion engine according to the preamble of claim 1.

State of the art

A lambda control, in conjunction with a catalytic converter, is today the most effective emission control method for an internal combustion engine, in particular of a motor vehicle. Only in combination with today available ignition and injection systems can be achieved very low exhaust emissions. The catalyst types used today have the property of reducing hydrocarbons, carbon monoxide and nitrogen oxides by more than 98% if the internal combustion engine is operated in a range of about 1% by the stoichiometric air-fuel ratio with lambda = 1. The lambda value indicates how far the actual air-fuel mixture deviates from the theoretically necessary mass ratio of 14.7 kg or 14.5 kg of air to 1 kg of fuel for complete combustion. The value of 14.7 kg applies to petrol and the value of 14.5 kg for diesel fuel. Lambda is the quotient of the supplied air mass and the theoretical air requirement.

A broadband lambda probe and a control unit for operating such a lambda probe are disclosed in DE 10 2008 001 697 A1. The operation comprises, in particular, the control of the lambda probe as well as the evaluation of the signals or data supplied by the lambda probe. The control unit comprises a signal conditioning unit, an A / D converter, a pump current regulator, a digital interface, a controller, an inner pump electrode connection, an outer pump electrode connection and a reference Conference electrode terminal. The signal conditioning unit is provided for determining an actual value for the pump current regulator and for determining further information about the operating state of the broadband lambda probe. The information can be output via the digital interface.

A pump voltage Up is applied to the pumping cell of the lambda probe, which voltage is adjusted as a function of a Nernst voltage corresponding to the oxygen concentration in the exhaust gas taken off at the Nernst cell with the aid of a pumping current controller. By means of the pumping current regulator, the pumping current Ip is adjusted or tracked so that the pumping voltage Up can be predetermined within

Borders lies.

A corresponding control unit in the form of an integrated circuit (IC) for controlling broadband lambda probes suitable for diesel and gasoline engines is marketed by the applicant under the name "CJ135." This control unit will be described below with reference to FIG.

By means of a control unit mentioned, a broadband lambda probe can be operated and monitored with the aid of a single ASIC (Application Specific Integrated Circuit). This ASIC serves, in particular, for providing a regulated pump current (Ip) and its detection, for detecting the internal sensor resistance (Ri) for temperature monitoring of the sensor and for monitoring and possibly protecting all sensor lines. DE 101 56 248 A1 discloses a broadband lambda probe which has only a single pumping cell, that is to say has a unicellular construction, and which can be operated according to the limiting current principle. The probe has two electrodes arranged on a solid electrolyte, wherein the first electrode (outer pumping electrode) extends into a reference gas via a reference or exhaust air channel and the second electrode (inner pumping electrode) extends into the measurement gas or exhaust gas via a diffusion barrier , To operate the probe, a voltage is applied to the electrodes, whereby in the case of lean exhaust gas, oxygen ions are moved from the anode to the cathode, that is from the inner electrode to the outer pumping electrode. Since the subsequent flow of oxygen molecules from the exhaust gas into the cavity surrounding the inner electrode is impeded by a diffusion barrier, the pumping current reaches above one Pump voltage threshold, a current saturation, the so-called limiting current. This limiting current is proportional to the oxygen concentration in the exhaust gas. Conversely, when the exhaust gas is rich, oxygen is pumped from the exhaust duct into the measuring space.

Disclosure of the invention

The invention is based on the finding that, in particular, for operating a single-cell, wide-band lambda probe, e.g. a said single-cell limit current probe, which has only two sensor lines, a said pumping current regulator is not required. Therefore, a broadband lambda probe of this type can be evaluated or monitored without a pumping current controller. In contrast to the known in the prior art "CJ135" ASIC, which includes a pumping regulator, the invention enables a relatively simple design and thus cost-realizable circuit arrangement for pumping current measurement and pumping voltage tracking By sufficiently high presetting of the pumping voltage, the lambda probe is kept in the limit current operation, This means that the total oxygen diffusing through the diffusion barrier to the inner electrode or the inner pumping electrode is pumped to the outer electrode or exhaust air electrode eg water decomposition effects result, whereby the measuring signal, namely the pumping current, is falsified.

A circuit arrangement according to the invention or a control unit having such a circuit arrangement comprises a measuring resistor with which the value of the pumping current and thus the lambda value can be determined. Of the

Pumping current is largely determined by the connected to the inner and outer pump electrode lambda probe. For example, the pump current required for the operation of the lambda probe can not be made available by a microcontroller or a voltage generator arranged in the microcontroller which supplies a pulse width modulated (PWM) voltage signal, which is usually required. can be generated by an additional circuit part, such as a suitable operation amplifier circuit, generated or provided.

The pumping current is thus not regulated, as in the prior art, but determined by means of the aforementioned measuring resistor. Based on the measured value determined in this way, the pump voltage is tracked using a uniform pump voltage generated by pulse width modulation and a downstream low-pass filter. This DC voltage is used in particular to keep the lambda probe in said limit current operating mode. Preferably, therefore, a characteristic curve is stored in a microcontroller which assigns the associated voltage value to a pump current value.

In order to enable a current flow of the pumping current in both current directions, a "virtual ground" arranged behind the measuring resistor can be provided.The virtual ground can serve as a current source and / or as a current sink and provide a constant voltage. In the normal operation of a self-igniting internal combustion engine (diesel engine), the lambda probe is mainly exposed to lean exhaust gas, however, the exhaust gas must be temporarily enriched, for example in the event of regeneration of the catalytic converter, in which case the pumping current flows in the other direction.

A measuring current pulse is applied to the evaluation circuit and thus also to the probe, and with the aid of the pump voltage, the internal resistance of the lambda probe and thus the probe temperature can be determined. This can also be used to diagnose fault conditions on electrical lines of the lambda probe.

Since the control unit according to the invention, which is suitable in particular for a single-cell broadband probe, does not require a pumping current regulator and, moreover, can be constructed from discrete components, in particular the manufacturing costs of the control unit can be considerably reduced.

Moreover, a control unit according to the invention has a considerably greater electrical or electromagnetic robustness, since it does not cause any vibration. has sensitive to the control loop and therefore less susceptible to vibration.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The circuit arrangement or control unit according to the invention can be used with the advantages described herein in an engine control unit of a self-igniting internal combustion engine for the operation and monitoring of a single-cell lambda probe in the case of a broader field of application of said broadband lambda probes, the invention will certainly be applicable in other areas ,

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

Brief description of the drawings

FIG. 1 shows a block diagram of a control unit known from the prior art for operating a broadband lambda probe.

Figure 2 shows schematically a known in the art limit current probe.

FIG. 3 shows a block diagram of a control unit according to the invention for operating a single-cell, wide-band lambda probe.

Description of exemplary embodiments

The control unit 10, which is known per se in terms of its structure (initially referred to as the IC "CJ135"), corresponds in its function to an evaluation module for a broadband lambda probe, and the control unit is therefore equipped with a broadband lambda probe 15. or data technology prevented. In addition, there is a signal connection with an external microcontroller (μθ) 20.

The control unit 10 comprises an analog / digital (A / D) converter 25, a filter 30 and an SPI (Serial Peripheral Interface) shift register 40. By means of the A / D converter 25, those supplied by the lambda probe 15 digitized analog measurement data for digital processing. By means of the filter 30, preferably a low-pass filter, the signal noise of the measurement signal supplied by the sensor is reduced. The thus filtered digital data is transmitted to the microcontroller 20.

The control unit 10 further comprises a switching matrix 33, which is operated by means of a control module 34 and is fed by a current generator 35. By means of the switching matrix 33, the inputs of the control unit and the type of evaluation of the measurement signals can be flexibly adapted or changed.

The aforementioned lambda controller is in this case in the microcontroller 20, the pumping current regulator is implemented in the control unit 10 (i.e., in the present case in CJ135).

FIG. 2 shows a limiting current probe described in DE 10 2006 030 437 A1 for determining the concentration of gas components in a gas mixture, the so-called measuring gas 100. The limiting current probe comprises a heater 160 in a lower region and a measuring chamber 130 in a central region a first electrode 140 and in an upper region a second electrode 150.

Between the first electrode, in the present case the inner pumping electrode 140, and the second electrode, in the present case the outer pumping electrode 150, extends a solid electrolyte, which together with the two electrodes forms a pumping cell

120 forms. The outer pump electrode 150 facing the gas mixture or sample gas 100 is protected from the sample gas 100 by a protective layer 110. Furthermore, the pumping cell 120 has an opening 105 in a central area, through which the measuring gas 100 passes via a diffusion barrier 135 into the measuring space 130 and thus to the inner pumping electrode 140. The outer pump electrode 150 is exposed to reference air. By applying a heating voltage (UH) 165, the gas sensor and in particular the pumping cell 120 are brought to an operating temperature at which the solid-state electrolyte has a sufficiently high oxygen-ion conductivity.

A pump voltage (Up) 170 is applied to both electrodes 140 and 150. If lean exhaust gas passes through the diffusion barrier 135 into the measuring space 130, the oxygen molecules of the exhaust gas are reduced to oxygen ions by means of the pumping voltage 170 at the inner pumping electrode 140, which acts as an anode, transported through the solid electrolyte to the outer pumping electrode 150, which acts as a cathode and released there as free oxygen again. The pumping voltage 170 is adjusted so that the oxygen entering through the diffusion barrier 135 is completely pumped to the outer electrode or exhaust air electrode 150, which acts as a cathode.

In order to avoid water decomposition effects which would falsify the measurement, a high pump voltage Up is not permanently set, however, in the context of a so-called "pump voltage tracking", the pump voltage (Up) 170 is adapted to the respective pump current (Ip) 175. The resulting pump current 175 is approximately proportional to the residual oxygen content in the exhaust gas, whereby such single cell sensors are also referred to as "proportional sensors". The pumping cell 120 can therefore be used in a relatively wide range for determining the air ratio lambda. However, such unicellular sensors usually only have a clear characteristic curve with relatively lean exhaust gas (lambda> 1) and are therefore preferably used in self-igniting internal combustion engines.

FIG. 3 shows a circuit arrangement according to the invention or a control unit according to the invention which has such a circuit arrangement and is preferably shown for operating a previously described single-cell limit current probe. A limit current probe 330 (not shown here) shown in FIG. 2 is connected to the circuit arrangement via a named IPE connection 343 (inner pumping electrode) and a named ALE connection 342 (outer pumping electrode or exhaust air electrode). The limit current probe 330 serves to generate a pumping current 304 mentioned above. The pumping current 304 determined by the limit current probe 330 is, as described above, a measure of the residual oxygen content in the exhaust gas. In the case of Ip = 0, lambda = 1. If the air-fuel mixture is relatively lean (lambda> 1), a pumping current Ip flows from the exhaust air electrode (ALE) 342 to the inner pumping electrode (IPE) 343 of the limit current probe. If, on the other hand, the mixture is relatively rich (lambda <1), then a pumping current Ip flows in the opposite direction.

A voltage generator 315 is used with the aid of a filter, in particular a low-pass filter 305, to generate the pump voltage (Up) 303, the value of the pump voltage 303 being dependent on the respective pumping current (Ip) 304 in a manner known per se by means of a pulse width-modulated ( The pumping current (Ip) 304 is provided in the present embodiment by a pumping current generator 405, which can be separated via a fourth switch (T4) 400 from the subsequent part of the circuit.

As indicated by the dashed line 380, such a pumping current generator 405 and the switch T4 (400) are not absolutely necessary, since the pumping current 304 can in principle also be provided by the microcontroller 310.

The PWM signal 307 is supplied by a voltage generator 315 and in the present embodiment is in the frequency range of about 20 to 30 kHz. It should be noted, however, that the present invention or its application is not limited to this frequency range. The generator 315 is arranged in an internal or external microcontroller (μθ) 310. The pump voltage 303 thus set can also be smoothed via a first low-pass filter 305. The pumping voltage 303 is read back into the microcontroller 310 via a second low-pass filter 306 and an analog-to-digital converter (ADC) 320.

The pumping current (Ip) 304 is determined by means of a measuring resistor 345. If necessary, for example for reasons of accuracy, the voltage drop across the measuring resistor can be amplified, eg by means of a differential amplifier (not shown) or by means of the ADC 320 already present in the microcontroller 310. By means of a characteristic 325 stored in the microcontroller 310 is generated from the pumping current 304, with an adjustable time delay, the pump voltage (Up) 303 to be generated.

In order for the pumping current (Ip) 304 to be able to flow in the two current directions 395, a "virtual ground" (VM) 355 is arranged behind the measuring resistor 345. The virtual ground 355 serves both as current source and as current sink in the present exemplary embodiment and supplies a fixed or constant voltage value behind the measuring resistor 345. If necessary, this voltage value can be read back, for example for reasons of accuracy, via an additionally arranged third low-pass filter 370. As indicated by the dashed line 375, the readback of the VM value is only preferred However, in order for the current to flow from the IPE 343 to the ALE 342, the voltage value at the ALE 342 must be lower than the voltage at the IPE 343. Because only in this case is this reverse current flow In the present embodiment, the value of the constant voltage is possible For example, 2.0 V, but may also be different, since it does not depend on the exact voltage value present.

In the upper part of the circuit, a first switch (T1) 360, which is likewise driven by the microcontroller 310, is additionally arranged. With the help of this switch, a current pulse is applied to the circuit or the probe. By voltage evaluation on the ALE 342 by means of the low-pass filter 306, the internal resistance of the probe (Ri) and thus the probe temperature can be determined. The measuring current required for this purpose is provided by a measuring current generator 385 in the present exemplary embodiment.

This circuit arrangement or a corresponding control unit can also diagnose fault conditions on the probe lines. For example, present short circuits can be detected with the aid of the described evaluation of the voltage potential applied downstream of the low pass 306 and of the voltage drop present at the measuring resistor 345, or a combination of both. By a suitable position of the first switch (T1) 360 and a likewise driven by the microcontroller 310 second switch (T2) 365 can be a diagnosis of cable breaks by means of

Plausibility be carried out. By means of the second switch (T2) 365 and a further third switch (T3) 390, a replacement reaction can be generated in the event of an error. Thus, the two switches 365, 390 can be opened, whereby the probe lines 330 are switched to high impedance.

In addition, with the aid of the aforementioned switches 360, 365 and a suitable programming of the microcontroller (μθ) 310, additional additional functions can be realized, e.g. a function for depolarizing the probe.

The described circuit arrangement can be implemented in the form of an ASIC-based control unit or also constructed from discrete components in a control unit of an internal combustion engine.

Claims

claims

1 . Control unit for operating in particular a single-celled broadband lambda probe of an exhaust aftertreatment system of an internal combustion engine, wherein the broadband lambda probe by means of a pumping voltage

(303) is maintained in the limit current operation, whereby a residual oxygen in the exhaust gas proportional pumping current (304) sets, and wherein the pumping voltage (303), depending on the self-adjusting pumping current

(304).

2. Control unit according to claim 1, characterized in that the pumping voltage (303) by means of a stored characteristic (325) from the pumping current (304) is determined.

3. Control unit according to claim 1 or 2, characterized in that the pumping current (304) by means of a measuring resistor (345) is determined.

4. Control unit according to claim 3, characterized in that the pumping voltage (303) is tracked on the basis of the determined pumping current (304) and by means of pulse width modulation (307) and the pulse width modulation (307) downstream low-pass filter (305).

5. Control unit according to claim 3 or 4, characterized in that the measuring resistor (345) is connected to a virtual ground (355).

6. Control unit according to claim 5, characterized in that the virtual mass (355) serves as a current source and / or current sink.

7. Control unit according to claim 5 or 6, characterized in that the virtual mass (355) provides a constant voltage.

8. Control unit according to one of the preceding claims, characterized in that by impressing a measuring current and taking into account the pumping voltage (303), the internal resistance of the lambda probe (330) and thus the probe temperature can be determined.

9. Control unit according to one of the preceding claims, characterized in that by suitable wiring (360, 365, 390) fault conditions on electrical lines of the lambda probe (330) are diagnosable.

10. Control unit according to one of the preceding claims, characterized by a circuit arrangement for carrying out the functions according to one of the preceding claims, which is constructed of discrete electrical or electronic components.

1 1. Control unit according to one of Claims 1 to 9, characterized by a circuit arrangement arranged in an ASIC for carrying out the functions according to one of Claims 1 to 9.

12. Integrated circuit, in particular ASIC, for the operation and / or monitoring of a particular unicellular broadband lambda probe by means of a circuit arrangement for carrying out the functions according to one of claims 1 to 9.