DE102007029029A1 - Lambda regulation method for use in internal combustion engine of motor vehicle, involves determining lambda deviation from rear sensor produced by rear lambda sensor and adapting conversion rule under consideration of determined deviation - Google Patents

Abstract

The method involves determining a lambda value (25) with the aid of a front sensor signal (21) and a conversion rule (23), where the front sensor signal is produced by a front lambda sensor (17). A lambda deviation is determined from a rear sensor signal (29) that is produced by a rear lambda sensor (19). The conversion rule is adapted with the aid of and/or under the consideration of the determined lambda deviation. A lambda modulation is regulated and/or adjusted with the aid of an engine control unit (7) of an internal combustion engine (1).

Description

The The invention relates to a method for λ control in a Internal combustion engine with a motor control for mixture formation, a arranged in an exhaust system of the internal combustion engine front λ-probe for producing a front oxygen content of a in the Exhaust system upstream of a arranged in the exhaust system Catalyst-guided exhaust gas characterizing front Probe signal and one in the exhaust system downstream the catalyst arranged rear λ-probe for generating one of a rear oxygen content of the downstream in the exhaust system Characterizing the catalyst led exhaust gas rear probe signal.

Internal combustion engine lambda control methods and apparatus are used to reduce emissions of harmful emissions to the environment. For this purpose, at least one catalyst can be arranged in the exhaust system of the internal combustion engine. In order to keep the catalyst at an optimum operating point, it is necessary to control the mixture preparation of the internal combustion engine with the aid of a lambda control in such a way that, at least in the mean value, a regulated lambda value is obtained which is as close as possible to 1.0. It is known to provide a front lambda control circuit with a front oxygen sensor arranged downstream of the combustion engine and upstream of the catalytic converter and a rear lambda control circuit with at least one rear oxygen sensor arranged downstream of the catalytic converter. Furthermore, it is known to influence the control quality by evaluating the probe signals. In addition, it is known to model the current oxygen fill level of the catalyst. The pamphlets DE 102 25 937 A1 . DE 196 06 652 A1 and DE 103 39 063 A1 exemplify such systems. The DE 4320881 A1 shows a combination of a heated λ probe with a jump-shaped or binary probe characteristic with another heated λ probe.

task The invention is an improved, in particular a more stable and / or more emission-efficient, λ-control at a Internal combustion engine, in particular using a λ-probe according to the Nernst principle.

The Task is in a method for λ control at a Internal combustion engine with a motor control for mixture formation, a arranged in an exhaust system of the internal combustion engine front λ-probe for producing a front oxygen content of a in the Exhaust system upstream of a arranged in the exhaust system Catalyst-guided exhaust gas characterizing front Probe signal and one in the exhaust system downstream the catalyst arranged rear λ-probe for generating one of a rear oxygen content of the downstream in the exhaust system Characterizing the catalyst led exhaust gas rear probe signal, solved with the following steps: Determining a λ value by means of the probe signal and a conversion rule, determining a λ deviation from the rear probe signal and adapting the conversion rule by means of and / or taking into account the determined λ deviation. The conversion rule or the resulting λ value can be used as input of the engine control of the Combustion engine, the control quality and thus also a possible influence unwanted λ deviation. therefore can by way of the feedback of the λ deviation acting on the conversion rule these are eliminated or at least reduced to a minimum, which results in an overall improved λ control.

A further preferred embodiment of the method has at least one of the following steps: rules and / or setting a λ-modulation by means of the engine control of the internal combustion engine, Determining an oxygen mass flow from the determined λ value and / or determining an oxygen level of the catalyst. With knowledge of the control algorithms of λ-modulation and with the determination of the oxygen mass flow can, for example by means of the catalyst model, the oxygen level of the catalyst can be determined.

A further preferred embodiment of the method comprises at least one of the following steps: regulating and / or setting the λ modulation, wherein the oxygen filling level is constant on average, in particular zero, and / or regulating and / or setting the λ modulation, wherein, during a first phase of rich mixture formation, an amount of oxygen discharged from the catalyst is substantially the same as an amount of oxygen introduced into the catalyst during a second phase of lean mixture formation. It is possible to calculate an oxygen balance of the catalyst, wherein the oxygen concentration of the catalyst remains constant or maintained on average. Under this assumption of a constant or balanced oxygen fill level, this variable does not have to be evaluated to adapt the conversion rule. Rather, this can be assumed to be constant during adaptation, ie taken into account as a constant variable or, at best, can not be included in the conversion rule. It is conceivable that the phases of lean and rich mixture formation follow each other directly. However, it is also conceivable to regulate the average over more than two phases and / or adjust, beispielswei se between the phases of rich or lean mixture formation a phase of stoichiometric mixture formation, ie with a λ value = 1, interpose or take into account an average over more than one period. Furthermore, it is conceivable to subdivide the phases of rich or lean mixture formation into further individual phases, for example lambda respectively λ falling in a phase and λ values held constant in each case. By rules and / or setting, any control and / or regulating method can be understood.

A preferred embodiment of the method has the following Steps to: adapting the conversion rule by means of and / or taking into account the determined λ deviation and by means of and / or taking into account the determined oxygen level. The oxygen level of the catalyst can, for example be determined by means of a suitable catalyst model. Of the Oxygen mass flow can be calculated from the determined λ value for example, with knowledge of the total exhaust gas mass flow through integration and can be used as input for serve the catalyst model: Advantageously, both Size information on the current quality of control, in particular the measuring section supply the λ control. Advantageously, it can be an adaptation the measurement path, so the conversion rule are derived, so that results in an overall improved λ control.

A further preferred embodiment of the method has at least one of the following steps: integrating the oxygen level, integrating the oxygen level to an absolute value and / or Integrate the oxygen level relative to one Output value related. The integrated value of the oxygen level can be included in the conversion rule. It is not absolutely necessary, the oxygen level as absolute value to determine, so that also an integration, beginning at a Any initial value may be sufficient. Advantageously, the Initial value reset under certain ideal conditions be and / or be redefined. This can be, for example at fixed, more or less random while the driving cycles of the internal combustion engine occurring ideal operating conditions respectively. However, it is also conceivable such an operating state deliberately cause by means of the engine control, wherein the initial value of the oxygen level can be reset can.

A Another embodiment of the method has the following Step on: Determining the λ-value by means of the front Probe signal, the conversion rule and a detected temperature the front λ-probe. Advantageously, temperature influences, that on the transfer characteristic of the front λ-probe be considered in the conversion rule. This results in a more accurate conversion of the probe signal in the λ value.

at a further preferred embodiment of the method the front λ probe is a jump λ probe. The jump λ-probe, for example, a sour oxygen sensor according to the Nernst principle. Jump λ probes are typically more cost effective compared to broadband λ probes manufacture. The proposed method allows despite the use of such a jump λ probe, the systemic in fat and lean exhaust gas compositions a relatively low, in particular tolerance-related, signal resolution can still have a good λ measurement and / or regulation.

The Task is also by a motor vehicle with a and / or equipped for the realization of a previously described Procedure solved.

Further Advantages, features and details emerge from the following Description, in which with reference to the drawing an embodiment is described in detail. Same, similar and / or functionally identical parts are provided with the same reference numerals.

It demonstrate:

1 a diagram of a λ control for an internal combustion engine;

2 a diagram of a front probe signal over the time of in 1 shown λ-control;

3 a diagram of a characteristic for converting the in 2 represented front probe signal in a front λ value; and

4 one by means of the characteristic 3 determined forward λ value over time together with a desired λ value.

1 shows a block diagram of a method for λ control in an internal combustion engine 1 , The internal combustion engine, not shown 1 has for λ control a front loop 3 and a rear loop 5 on. There is also a motor control 7 or engine control unit for controlling a mixture composition of the internal combustion engine 1 intended. The engine control 7 is in 1 by means of a dashed line indicated as part of the front control loop 3 a front regulator 9 and as part of the rear loop 5 a rear regulator 11 the rear loop 5 on.

The internal combustion engine 1 is an exhaust system 13 with a catalyst 15 downstream. As a measuring element of the front control loop 3 indicates the exhaust system 13 a front λ-probe upstream of the catalyst 17 on. As a measuring element of the rear control loop 11 indicates the exhaust system 13 also a catalyst 15 downstream rear λ probe 19 on.

By means of the front λ-probe 17 , which is designed as a jump λ-probe, for example according to the Nernst principle, can be a front probe signal 21 be won. The front probe signal 21 characterizes an oxygen content of one in the exhaust system 13 guided exhaust gas mass flow upstream of the catalyst 15 , The front probe signal 21 can by means of a conversion rule 23 in a λ-value 25 be converted. The by means of the conversion rule 23 calculated λ value 25 can be from a setpoint 27 subtracted and the front regulator 9 be supplied.

The front loop 3 or the associated front controller 9 can be designed to control a so-called λ-modulation, where λ-values> 1 and <1 in the mixture formation of the internal combustion engine 1 can be set, with a λ-value = 1 is set as the target on average.

The rear loop 5 can by means of the rear λ-probe 19 , which may be designed, for example and usually as a jump λ probe, determine an undesirable λ deviation. For this purpose, a rear probe signal 29 the rear λ probe 19 the rear regulator 11 are supplied to compensate for the unwanted λ deviation to the setpoint 27 a correction value 31 can add, so for example, a trim control allows. The correction value 31 is in 1 shown in dashed lines.

Advantageously, the rear regulator 11 an additional active connection for influencing the front control loop 3 on. For this purpose, the rear regulator 11 to the conversion rule 23 acting adaptively or correctively. Advantageously, it is possible, with a determined unwanted λ deviation by means of the rear λ-probe 19 the conversion rule 23 of the front control loop 3 adapt so that the unwanted λ deviation is eliminated or at least reduced to a minimum. Due to this influence on a measuring section 32 of the front control loop 3 it is conceivable on the operative connection by means of the correction value 31 to refrain, so no correction value 31 in the rear regulator 11 to correct the setpoint 27 to generate. Advantageously, by means of the adaptation of the conversion rule 23 Errors and / or tolerances of the front λ-probe 17 be eliminated. In addition, other disturbances can be excluded. To take into account only long-term changes or errors, a corresponding attenuation can be provided.

From the determined λ value 25 of the front control loop 3 can in a calculation step 33 an oxygen mass flow 35 of the exhaust system 13 guided exhaust gas mass flow of the internal combustion engine 1 be calculated. In an integration step 37 can the oxygen mass flow 35 , For example, by means of a suitable catalyst model of the catalyst 15 to an oxygen level 39 be integrated. The by means of the steps 33 and 37 obtained data on the oxygen filling level of the catalyst 15 can be used as an additional input to the front regulator 9 serve, for example, to regulate the λ-modulation oxygen-balanced, so in addition the oxygen level 39 of the catalyst 15 to regulate, for example, to maintain a constant level.

By means of a dashed line is indicated that the oxygen level 39 also as an input for the conversion rule 23 can serve, especially if this is not regulated, so only determined. Advantageously, it is possible to both the oxygen level 39 as well as by means of the rear regulator 11 determined λ deviation to adapt the conversion rule 23 to use. Assuming a constant oxygen level of the catalyst 15 or one by means of the front controller 9 held constant oxygen level, can be advantageous to the active compound between the integration step 37 and the conversion rule 23 be waived.

It is conceivable as an additional input for the conversion rule 23 also a temperature 41 the front λ-probe 17 to take into account what by means of a dashed line of action in 1 is indicated. The temperature 41 can therefore also be used correctively. The temperature 41 , For example, a temperature of the front λ-probe 17 , preferably an element temperature, may be determined by suitable methods, such as a temperature model of the front λ-probe 17 or determined by a measurement.

2 shows a diagram of the front probe signal 21 over time, where in an x-axis, the time between 0 and 10 seconds and in a y axis, a voltage between 0 and 0.9 V are plotted. According to 2 the front probe signal oscillates 21 by values between approx. 0.1 V and 0.75 to 0.8 V within a period of approx. 4 seconds.

3 shows a diagram of a characteristic 43 the conversion rule 23 for the front probe signal 21 the front λ-probe 17 , On an x-axis is in 3 in the 2 Probe voltage of the front λ probe plotted on the y-axis 17 between values of 0-1V. By means of the characteristic 43 can each have a specific probe voltage of the front λ-probe 17 be assigned a λ value. In the 3 detectable λ values correspond to the λ value 25 and are in 3 plotted on a y-axis in values between 0.9 and 1.1.

4 shows a diagram of the means of the determined λ value 25 determined oxygen mass flow 35 together with the setpoint 27 over time, where in an x-axis the 4 the time is between 0 and 10 seconds. On a y-axis of the chart in 4 a λ value between 0.95 and 1.05 is plotted. The oxygen mass flow 35 is drawn without dimensions, wherein the λ = 1 line an oxygen mass flow 35 equal to zero. The oxygen mass flow 35 For example, by means of the formula (1 - 1 / λ) · exhaust gas mass flow in the exhaust system 13 guided exhaust gas can be determined. In 4 It can be seen that phases of rich mixture formation and lean mixture formation alternate in an oscillating manner. In 4 is for example a first phase 45 with λ values <1, ie a rich mixture composition and a second phase 47 with λ values> 1, ie a lean mixture composition recognizable. The phases 45 and 47 follow each other and repeat themselves in this rhythm oscillating, whereby also the oxygen mass flow 35 this oscillation of the impressed setpoint 27 follows. As in 4 recognizable, the front regulator can 9 be adjusted so that under the first phase 45 of the oxygen mass flow 35 a first surface 49 results in the same area with a second surface 51 under the second phase 47 is. The surfaces 49 and 51 can be a measure of a catalyst 15 represent supplied or withdrawn amount of oxygen. If successful, the first surface 49 coextensive with the second surface 51 regulate, can of a constant mean oxygen content of the catalyst 15 be assumed.

By means of a first double arrow 53 is in 3 a horizontal shift of the characteristic 43 indicated, as it can be given for example by aging or tolerances. In 4 is by means of a second double arrow 55 the effect of such a shift on the thereby insufficient accurately determinable oxygen mass flow 35 indicated in the sense of a measurement error. One in alignment 3 shifted to the left characteristic causes, for example, a shift of the determined oxygen mass flow 35 in alignment with the 4 downward.

A third double arrow 57 indicates in 4 one of these actually incorrect or inaccurate determined oxygen mass flow 35 caused reaction of the rear regulator 11 indicating the resulting deviation of the mean λ setpoint 27 recognizes and tries to compensate by a shift of the same. This regulator intervention of the rear regulator 11 in turn, can be used to plot the characteristic 43 the conversion rule 23 to adjust so that again a more accurate λ value 25 determine, for example, to shift the characteristic horizontally in the opposite direction. As a result, the measurement error or the error of the test section 32 compensated, so now a correct oxygen mass flow 35 can be determined. The controller intervention of the rear regulator 11 is automatically canceled as a result of the compensation, which can be maintained, for example, until a subsequent compensation. Advantageously, the optimization of the control attacks exactly where the cause of the change in the control quality is, namely at a measuring quality deteriorating change in the characteristic 43 caused for example by aging and / or tolerances. A shift of the setpoint value to an actually incorrect mean preset value (third double arrow 57 ), is after the adaptation of the conversion rule 23 with the characteristic 43 not necessary anymore.

Preferably, the Sauerstoffein- and -austrag in the catalyst 15 be set so that on average a constant oxygen level is maintained. Then an adjustment of the conversion rule 23 of the front probe signal 21 in the λ value 25 exclusively by means of the determined λ deviation of the rear control loop 5 respectively. The control of the λ modulation is then such that the in the catalyst 15 registered amount of oxygen during the lean half-wave (second phase 47 ) is the same as the amount which occurs during the rich half wave (first phase 45 ) is discharged again. The determination of the mean λ deviation downstream of the catalyst 15 For example, with a λ-sensor, for example, the rear λ-probe 19 and a known method for λ trim control on the basis of a suitable catalyst behavior model. This so determined λ-deviation downstream of the catalyst 15 may be used to suitably adapt the conversion rule 23 of the front probe signal 21 USAGE det, for example, by moving, partial shifting, changing the slope of the curve 43 and / or the like.

Furthermore, it is conceivable that in the conversion of the front probe signal 21 also the respective temperature 41 the front λ-probe 17 , preferably the element temperature, is taken into account corrective. The temperature 41 The probe can be determined with a suitable method, for example a temperature model of the sensor.

1

internal combustion engine

3

front loop

5

rear loop

7

motor control

9

front regulator

11

rear regulator

13

exhaust system

15

catalyst

17

front λ probe

19

rear λ probe

21

front probe signal

23

conversion rule

25

λ-value

27

setpoint

29

rear probe signal

31

correction value

32

measuring distance

33

calculation step

35

Oxygen mass flow

37

integration step

39

Oxygen level

41

temperature

43

curve

45

first phase

47

second phase

49

first area

51

second area

53

first double arrow

55

second double arrow

57

third double arrow

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10225937 A1 [0002]
• - DE 19606652 A1 [0002]
• - DE 10339063 A1 [0002]
• - DE 4320881 A1 [0002]

Claims (8)

Method for λ control in an internal combustion engine ( 1 ) with a motor control ( 7 ) for mixture formation, one in an exhaust system ( 13 ) of the internal combustion engine ( 1 ) arranged front λ-probe ( 17 ) for detecting a front oxygen content of a in the exhaust system ( 13 ) upstream of an exhaust system ( 13 ) arranged catalyst ( 15 ) guided exhaust gas characterizing front probe signal ( 21 ) and one in the exhaust system ( 13 ) downstream of the catalyst ( 15 ) arranged rear λ-probe ( 19 ) for generating a rear oxygen content of the in the exhaust system ( 13 ) downstream of the catalyst ( 15 ) guided exhaust gas characterizing rear probe signal ( 29 ), comprising the following steps: determining a λ value ( 25 ) by means of the front probe signal ( 21 ) and a conversion rule ( 23 ), - determining a λ deviation from the rear probe signal ( 29 ), - adaptation of the conversion rule ( 23 ) by means of and / or taking into account the determined λ deviation. Method according to one of the preceding claims, with at least one of the following steps: - Controlling and / or setting of a λ-modulation by means of the motor control ( 7 ) of the internal combustion engine ( 1 ), - determining an oxygen mass flow ( 35 ) from the determined λ value ( 25 ), - determining an oxygen level ( 39 ) of the catalyst ( 15 ). Method according to claim 2, comprising at least one of the following steps: - regulating and / or adjusting the λ-modulation, wherein the oxygen level ( 39 ) is constant on average, in particular zero, - controlling and / or adjusting the λ-modulation, wherein during a first phase ( 45 ) a rich mixture formation one from the catalyst ( 15 ) discharged oxygen amount ( 49 ) is essentially the same size as one during a second phase ( 47 ) a lean mixture formation in the catalyst ( 15 ) registered amount of oxygen ( 51 ). Method according to one of claims 2 or 3, with the following step: - adapting the conversion rule ( 23 ) by means of and / or taking into account the determined λ deviation and by means of and / or taking into account the determined oxygen fill level ( 39 ). Method according to one of the preceding two claims, with at least one of the following steps: - Integrating the oxygen level ( 39 ), - integrating the oxygen level ( 39 ) to an absolute value, - integrating the oxygen level ( 39 ) relative to an initial value. Method according to one of the preceding claims, with the following step: determining the λ value ( 25 ) by means of the front probe signal ( 21 ), the conversion rule ( 23 ) and a determined temperature ( 41 ) of the front λ-probe ( 17 ). Method according to one of the preceding claims, wherein it is in the front λ-probe ( 17 ) is a jump λ probe. Motor vehicle with and / or equipped for Realization of a method according to one of the preceding claims.