WO2017144222A1

WO2017144222A1 - Method and device for operating a lambda probe in an exhaust gas channel of an internal combustion engine

Info

Publication number: WO2017144222A1
Application number: PCT/EP2017/051597
Authority: WO
Inventors: Florian Zink
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2016-02-24
Filing date: 2017-01-26
Publication date: 2017-08-31
Also published as: DE102016202854A1

Abstract

The invention relates to a method for operating a lambda probe (20) in an exhaust gas channel (12) of an internal combustion engine (10), wherein the lambda probe (20) is arranged in the exhaust gas channel (12) upstream of a catalyst (14), wherein the lambda probe (20) has a heating element (22), wherein the operating temperature of the lambda probe (20) is set by means of a heating controller (24) of the heating element (22), and wherein an exhaust gas temperature of the internal combustion engine (10) is determined by means of an internal resistance of the lambda probe (20), wherein a reference temperature is determined by means of a temperature sensor (16), an internal resistance (Ri) of the heating element (22) is measured at the determined reference temperature, a defined heating voltage is applied to the heating element (22), a step response of the internal resistance of the heating element (22) is evaluated, and the heating resistance (Rh) of the heating element (22) is adjusted on the basis of the step response. The invention further relates to a device for performing such a method and to a control unit (18) for performing such a method.

Description

description

Method and device for operating a lambda probe in an exhaust duct of a

Internal combustion engine

The invention relates to a method for operating a lambda probe in an exhaust passage of an internal combustion engine and to an apparatus for carrying out such a method according to the preambles of the independent claims.

In motor vehicles with an internal combustion engine, in particular with a petrol engine, today three-way catalytic converters for exhaust aftertreatment standard. The internal combustion engines are controlled by lambda probes alternately by a stoichiometric combustion air ratio, so that such three-way catalysts can develop their maximum efficiency with respect to the conversion of harmful exhaust gas components. In this case, a temperature measurement in the exhaust passage can provide important information about the condition of the exhaust system. Thus, for example, by a temperature measurement in the exhaust passage, an intervention in the engine control of the engine take place in order to avoid overheating of components for exhaust aftertreatment of the internal combustion engine. Furthermore, via the temperature measurement, the lambda control can be improved in such a way that the

Measurement accuracy of the lambda probes increases and thus the internal combustion engine can be adjusted in a narrower window to a stoichiometric combustion air ratio.

This reduces the raw emissions of the internal combustion engine and thus the total emissions of the motor vehicle. Temperature sensors are known from the prior art, which measure an exhaust gas temperature and this information to the engine control unit of the

Send combustion engine. However, these sensors are relatively expensive, so in the

Efforts have already been made in the past to determine the exhaust gas temperature via the heating resistor of a heated lambda probe.

From DE 10 2008 01 1 833 A1 a method for controlling a lambda-controlled exhaust system of an internal combustion engine is known, wherein the exhaust system has at least one catalyst and at least one heating element for heating the lambda probe to an operating temperature. It is envisaged that the performance of the heating element is determined and at least one corrected control parameter is used by the heating element control for controlled heating of the heating element. The invention is based on the object of further improving such a method and, using temperature sensors already present on the motor vehicle

to provide improved information about the temperature in the exhaust duct.

The object is achieved by an inventive method for operating a lambda probe in an exhaust passage of an internal combustion engine, wherein the lambda probe in the

Exhaust passage is arranged upstream of a catalyst, wherein the lambda probe a

Has heating element, wherein the operating temperature of the lambda probe by means of a

Heating controller of the heating element is set, wherein an exhaust gas temperature of the

Internal combustion engine is determined by an internal resistance of the lambda probe, and wherein by means of a temperature sensor, a reference temperature is determined at the determined reference temperature an internal resistance of the heating element is measured, the heating element is acted upon by a defined heating voltage, a step response of

Internal resistance of the heating element is evaluated and based on the step response, an adaptation of the heating resistance of the heating element takes place. This is an individual

Compensation of component scattering of the heating resistor of the lambda probes possible so that lambda probes-individually a temperature-resistance curve of the lambda probe can be calculated and thus an improved determination of the temperature in the exhaust passage based on the internal resistance of the respective lambda probe is possible.

According to an advantageous embodiment of the method it is provided that at a first time a first resistance of the heating element and at a later time a second resistance of the heating element is evaluated. By a two-fold evaluation of the internal resistance of the heating element, a simple creation of a correction function of the lambda probe is possible.

Preferably, the adaptation of the resistor takes place as a function of three

Resistance measurements of the heating element, wherein a first resistance measurement takes place at a temperature determined by the temperature sensor and two more

Resistance measurements are carried out at unknown temperatures and based on the measured internal resistance R, a lambda probe individual heating resistor R _{h is} calculated for the heating element of the lambda probe. There are thus three temperature measurements, one at the known temperature and two at unknown temperatures. It can be one

Relationship between the internal resistance R, and the heating resistor R _h are made to the size of the lambda probe-individual heating resistor R _h or to conclude a deviation from a heating resistor of a standard lambda probe. As a result, component variations in the heating resistor can be compensated and thus an improved model for calculating the exhaust gas temperature can be provided.

According to an advantageous embodiment of the method is provided that as

Reference temperature is the ambient temperature is provided. In general, it is on

Motor vehicles a sensor for detecting the ambient temperature exists

For example, to provide the driver via a display with this information to regulate the heating or air conditioning of the vehicle or to warn the driver against black ice. By such a temperature sensor and accurate

Temperature measurement, the exhaust gas temperature model can be made plausible by a sensor value, which improves the modeling over the entire exhaust system of the internal combustion engine.

In a preferred embodiment of the invention, it is provided that an adapted

Heating resistor R _{h is} stored in a control unit of the internal combustion engine. Thus, the corrected heating resistor is available for the further operation of the internal combustion engine and does not have to be constantly redetermined. In addition, the measurement can be used to correct the

Heating resistor R _h are repeated at regular intervals to compensate for aging of the lambda probe or a change in the heating resistance over the life of the lambda probe.

In a further preferred embodiment of the invention, it is provided that the method is started or carried out before a starting process of the internal combustion engine. Before the start of the internal combustion engine or after a longer standstill of the internal combustion engine or the motor vehicle, the temperature of the lambda probe substantially corresponds to the ambient temperature. Thus, the internal resistance R, of the heating resistance of the lambda probe can be determined at a precisely known temperature, whereby a stable support point for the model for calculating the exhaust gas temperature is formed.

According to a preferred embodiment of the method it is provided that the

Method by a door contact switch, a buckle sensor or a sensor for detecting a seat occupancy of a motor vehicle is started. Before starting a motor vehicle, the driver usually opens the driver's door, sits on the driver's seat, closes the belt and starts the vehicle and thus the internal combustion engine. Consequently are a door contact switch, a buckle sensor or a sensor for detecting a seat occupancy of the driver's seat well suited to start before starting the engine, a corresponding method. In this case, appropriate warning devices are usually present both for a non-closed door contact or for a non-applied seat belt, the signal simply to the control unit of the

Internal combustion engine can be forwarded to start the process.

According to the invention, a device for correcting a characteristic curve of a lambda probe in an exhaust duct of an internal combustion engine is proposed, wherein a catalytic converter is arranged in the exhaust duct, wherein in the flow direction of an exhaust gas of the internal combustion engine through the exhaust duct upstream of the catalyst, the lambda sensor is arranged, wherein the operating temperature of the lambda probe means a heating controller of the heating element is adjustable, wherein an exhaust gas temperature of the internal combustion engine by a

Internal resistance of the lambda probe can be determined, wherein a temperature sensor is provided for determining a reference temperature, and wherein the device comprises a control unit. By such a device can be carried out in a simple manner described in the preceding sections method. With such a device, an improved calculation of the temperature in the exhaust duct based on the heating resistance of the lambda probe can be done.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

The invention is described below in embodiments with reference to the associated

Drawings explained. Show it:

1 shows a motor vehicle with a device according to the invention for operating a

lambda probe

Figure 2 is a flow chart for carrying out a method according to the invention.

1 shows a motor vehicle 32 with an internal combustion engine 10. The internal combustion engine 32 has an exhaust gas channel 12, in which a catalytic converter 14, preferably a three-way Catalyst, is arranged. The internal combustion engine 10 is arranged upstream of the catalytic converter 14 via an exhaust gas flow direction of an exhaust gas of the internal combustion engine 10

Lambda probe 20 controlled by a control unit 18, wherein the internal combustion engine 10 is preferably operated alternately with low excess air and low fuel excess by a stoichiometric combustion air ratio. The lambda probe 20 is preferably designed as a broadband probe and has a controllable heating element 22, preferably a heating resistor on. To control the heating element 22 is a

Heating controller 24 is provided, which, for example, in the control unit 18 of the

Internal combustion engine 10 may be integrated or formed as a separate component.

On the motor vehicle 32, a temperature sensor 16 is arranged, with which a, preferably substantially constant temperature, in particular the

Ambient temperature, can be detected. On the motor vehicle 32 sensors 26, 28, 30 are further installed, which are designed as a door contact switch 26, as a buckle sensor 28 or as a sensor 30 for detecting the seat occupancy.

During operation of the internal combustion engine 10, the lambda probe 20 is heated both via the hot exhaust gas of the internal combustion engine and via the heating element 22 and regulated to a predefined operating temperature. In the case of hot exhaust gas, in principle the heating power requirement to the electric heating element 22 is low because a larger heat flow is supplied to the lambda probe 20 via the exhaust gas. The electric heating element 22 is based on an ohmic resistance. The applied voltage U is quadratically proportional to the heating power of the heating element 22. The heating resistance R _{h of} the heating element 22 determines how much voltage has to be applied to regulate the target temperature. The target value of this regulation is the internal resistance R, of the heating element 22 of the lambda probe 20.

The functional relationship can be described as follows:

P _h = U ^* l = U ² / R _h

Where P _{h is} the heating power, U the heating voltage, I the flowing current and R _h the

Heating resistor are.

The heating resistor is subject to manufacturing tolerances, so that during operation of the lambda probe 20 different heating powers are required to achieve the target internal resistance R ,. These tolerances must be adapted. Therefore, a comparison to existing ones Temperature sensors 16 helpful. This is preferably carried out in cold and stationary internal combustion engine 10 via a sensor for detecting the ambient temperature. The control unit 18 can start, for example via a door contact sensor 26, an adaptation routine with which a defined heating voltage U _{h is brought} to the lambda probe 20 and the step response of the internal resistance R, of the heating element 22

is evaluated. The gradient of the internal resistance R is higher for lambda probes 20 with a lower heating resistance R _{h of} the heating element 22 than for lambda probes 20 with a maximum permissible heating resistance.

The temperature of the lambda probe is proportional to the internal resistance R, of the heating element 22. The following applies: T ~ R, where R, the internal resistance of the heating element 22 and T is the temperature of the lambda probe 20.

The internal resistance R, is also proportional to the introduced heating power P _h. The following applies: R, ~ P _h . Thus, the temperature at the lambda probe 20 is inversely proportional to the heating resistance R _h . The following applies:

FIG. 2 shows a flow diagram of a method according to the invention for operating a lambda probe 20.

In a first method step <100>, the ambient temperature is determined by the

Temperature sensor 16 measured. In a second process step <1 10> takes place

Measurement of the internal resistance R, at the time t ₀ , ie at ambient temperature and before the lambda probe 20 or the heating element are acted upon by a defined heating voltage. In a further method step <120>, a defined

Heating voltage U _{h given} to the heating element 22 at cold lambda probe 20. At a first time t-1, in a method step <130>, a second measurement of the

Internal resistance R, of the heating element 22. After another delay time has elapsed, a second, later time t ₂ re-measures the internal resistance R, of the heating element 22. In a following process step <140>, the adaptation routine is ended and the learned, adapted value of Heating voltage R _h stored in the control unit 18.

By making three measurements of the internal resistance R ,, one at a known (ambient) temperature and two more at unknown temperatures, a Relationship between R, and R _h are made to close on the size of the adapted heating resistor R _h or the distance to a normalized heating element 22.

During operation of the internal combustion engine 10, the lambda probe 20 is heated both with the electric heating element 22 and by the exhaust gas of the internal combustion engine 10. With the known and adapted heating resistor R _{h of} the heating element 22 and the applied heating voltage U _h can thus be clearly and reliably closed to the temperature of the exhaust gas at the lambda probe 20. Thus, the disadvantages of an unadaptierten heating element 22 are overcome and thus greater accuracy in the

Temperature determination achieved. By a more accurate temperature determination over this

Method, the exhaust gas temperature model may provide an additional sensor value for

Achieve plausibility that enhances modeling across the entire exhaust system.

LIST OF REFERENCE NUMBERS

10 internal combustion engine

12 exhaust duct

14 catalyst

16 temperature sensor

18 control unit

20 lambda probe

22 heating element

24 heating controller

26 door contact switch

28 buckle sensor

30 Seat occupancy sensor

32 motor vehicle

I current

P _h heating power

R _h heating resistor

R, internal resistance

T temperature

U voltage t ₀ measuring time before applying the heating voltage t-ι first measurement time

t ₂ second measuring time

Claims

claims

1 . Method for operating a lambda probe (20) in an exhaust gas duct (12) of an internal combustion engine (10), wherein the lambda probe (20) is arranged in the exhaust gas duct (12) upstream of a catalytic converter (14), wherein the lambda probe (20) comprises a heating element ( 22), wherein the operating temperature of the lambda probe (20) by means of a heating controller (24) of the heating element (22) is set, and wherein an exhaust gas temperature of the internal combustion engine (10) by an internal resistance of the lambda probe (20) is determined, characterized in that by means of a

Temperature sensor (16) is determined a reference temperature at the determined reference temperature an internal resistance (R,) of the heating element (22) is measured, the heating element (22) with a defined heating voltage (U _h ) is applied, a step response of the internal resistance (R, ) of the heating element (22) is evaluated and based on the step response, an adaptation of the heating resistor (R _h ) of the heating element (22).

2. The method according to claim 1, characterized in that at a first time (t-ι) a first resistance of the heating element (22) and at a later time (t ₂ ), a second resistance of the heating element (22) is evaluated.

3. The method according to claim 2, characterized in that the adaptation of the

Resistance in dependence on three resistance measurements of the heating element (22) takes place, wherein a first resistance measurement takes place at a temperature determined by the temperature sensor (16) and two further resistance measurements are carried out at unknown temperatures and based on the measured internal resistance (Ri) a probe-individual heating resistor (R _h ) for the heating element (22) of

Lambda probe (20) is calculated.

4. The method according to any one of claims 1 to 3, characterized in that as

Reference temperature, the ambient temperature is selected.

5. The method according to any one of claims 1 to 4, characterized in that a

adapted heating resistor (R _h ) in a control unit (18) of the internal combustion engine (10) is stored.

6. The method according to any one of claims 1 to 5, characterized in that the method is started before a starting operation of the internal combustion engine (10)

or is performed.

7. The method according to claim 6, characterized in that the method by a door contact switch (26), a buckle sensor (28) or a sensor (30) for detecting a seat occupancy of a motor vehicle (32) is started.

8. Control unit (18) with a program code, which is stored on a machine-readable carrier, for carrying out a method according to one of claims 1 to 7, when the program on a computing device, in particular on a control unit (18) of the internal combustion engine (10), is performed.

9. A device for correcting a characteristic curve of a lambda probe (20) in an exhaust passage (12) of an internal combustion engine (10), wherein in the exhaust passage (12) a catalyst (14) is arranged, wherein in the flow direction of an exhaust gas of the internal combustion engine (10) the exhaust gas duct (12) upstream of the catalyst (14), the lambda probe (20) is arranged, wherein the operating temperature of the lambda probe (20) by means of a heating controller (24) of the heating element (22) is adjustable, wherein an exhaust gas temperature of the internal combustion engine (10) an internal resistance of the lambda probe (20) can be determined, characterized in that a temperature sensor (16) is provided for determining a reference temperature and that the device has a control device (18), wherein the device is set up, a method according to one of

Perform claims 1 to 7.

10. The device according to claim 9, characterized in that the lambda probe (20) is designed as a broadband probe.