DE102008002510B4 - Method for operating a reagent dosing device and device for carrying out the method - Google Patents

Abstract

Method for operating a reagent metering device (20) which meters a reagent into an exhaust gas duct (26) of an internal combustion engine (12) of a motor vehicle (10), in which the metered quantity is specified using an electromagnetically actuated metering valve (24) which is equipped with a pulse-width-modulated control signal (s_DV), characterized in that the pulse-width-modulated control signal (s_DV) of the metering valve (24) is defined as a function of the driving speed (v) of the motor vehicle (10), a driving speed threshold value (v_SW) being provided and that the pulse-width-modulated control signal (s_DV) is defined only when the vehicle speed falls below the threshold value (v_SW) as a function of the vehicle speed (v) of the motor vehicle (10).

Description

The invention is based on a method for operating a reagent metering device, which meters a reagent into an exhaust gas duct of an internal combustion engine of a motor vehicle, and on a device for carrying out the method according to the species of the independent claims.

The present invention also relates to a control unit program and a control unit program product.

State of the art

The DE60114423T2 discloses an invention relating to an exhaust emission control device for purifying exhaust gas emitted from an internal combustion engine capable of lean burn.

In the DE 199 03 431 A1 describes a method for operating an internal combustion engine in whose exhaust gas area an SCR catalytic converter (Selective Catalytic Reduction) is arranged, which reduces the nitrogen oxides contained in the exhaust gas of the internal combustion engine to nitrogen using a reagent. The reagent or a precursor of the reagent is preferably dosed as a function of the operating parameters of an internal combustion engine, such as the speed and the injected fuel quantity. Furthermore, the dosing preferably takes place as a function of exhaust gas parameters such as the exhaust gas temperature or the operating temperature of the SCR catalytic converter. As a reagent, for example, the reducing agent ammonia is provided, which can be obtained from a urea-water solution. The dosage of the reagent or the starting materials of the reagent must be carefully determined. If the dosage is too low, the nitrogen oxides in the SCR catalytic converter can no longer be completely reduced. Too high a dosage leads to reagent slippage, which on the one hand can lead to an unnecessarily high consumption of reagent and on the other hand, depending on the nature of the reagent, to an unpleasant odor nuisance.

In the DE 10 2006 044 080 A1 (not previously published) describes a method for operating a metering valve which is implemented as an electromagnetically actuated valve. A pulse-width-modulated metering signal is applied to the metering valve, which determines the metering of a reagent to be introduced into an exhaust gas duct of an internal combustion engine. The opening duration of the dosing valve is limited to a minimum opening duration during which the dosing valve is still fully open, which is defined in such a way that a spray mist is always produced during dosing. This prevents the reagent from crystallizing out. The known method thus ensures exact dosing on the one hand and counteracts clogging of the dosing valve on the other hand. The minimum opening time depends on several parameters such as the temperature and the operating voltage of the dosing valve magnet and the reagent pressure.

In the DE 103 06 134 A1 describes an exhaust gas aftertreatment device in which a dosing agent is also sprayed into the exhaust gas duct of an internal combustion engine. A swirler is provided in the housing upstream of an aftertreatment element which swirls the exhaust gases to enhance mixing upstream of the aftertreatment element. In addition, an acoustic tube is provided in the housing, which should contribute to the exhaust noise insulation. The acoustic tube at least partially encloses the turbulence device.

The DE 10 2006 006 881 A1 describes a method for operating an adjustment drive with a pulse width modulated positioning signal. The position of the part to be positioned depends on the duty cycle of the pulse width modulated positioning signal. A periodic change in the periods of the pulse-width-modulated position signal is provided. This procedure makes it possible to minimize the formation of mechanical resonances of the part to be positioned and thereby minimizes the emission of background noise. An exhaust gas recirculation valve, for example, is provided as the part to be positioned.

In the DE 43 10 859 C2 describes a method for positioning a throttle valve of an electric motor controlled by a pulse-width-modulated positioning signal, in which a linear relationship is provided between the duty cycle of the pulse-width-modulated positioning signal and the desired position value.

In addition to specifying a pulse-width-modulated positioning signal with a constant period and variable pulse durations, a pulse-width-modulated signal with a fixed pulse duration and a variable period can alternatively be provided.

The DE 10 2007 044 807 A1 (not previously published) specifies a method for operating an electromagnetically actuated metering valve, which is acted upon by a pulse-width-modulated metering signal, which introduces the metering of a gas into an exhaust gas duct of an internal combustion engine lowing reagent or a precursor of the reagent determines. A clock signal is provided, the period of which is less than the period of the pulse width modulated dosing signal. The period of the pulse width modulated dosing signal is set as a function of a dosing request signal to multiples of the period of the clock signal. This procedure enables the dosage to be quickly adapted to the dosage requirements. The effects of the alternating activation of the dosing valve in the context of clocked operation with a pulse width modulated dosing signal on the noise emission are not considered.

The invention is based on the object of specifying a method for operating a reagent metering device, which meters a reagent or a precursor of a reagent into an exhaust gas duct of an internal combustion engine, and a device for carrying out the method, in which the noise emission is optimized.

The object is achieved in each case by the features specified in the independent claims.

Disclosure of Invention

The procedure according to the invention for operating a reagent metering device is based on a metering operation in which a reagent is metered into an exhaust gas duct of an internal combustion engine of a motor vehicle, the metered quantity being specified with an electromagnetically actuated metering valve which is controlled with a pulse width modulated control signal. According to the invention it is provided that the pulse width modulated control signal of the metering valve is defined as a function of the driving speed of the motor vehicle.

Due to the switching processes of the metering valve, normal metering operation can lead to noises which are no longer a problem when the motor vehicle is driving at higher speeds outdoors, since they are drowned out by other driving noises. The noises arise in particular because the switching process of the metering valve excites the elastic mechanical structure surrounding the metering valve, for example a valve adapter, to vibrate, which are transmitted from the surface of the structure to the surrounding air and radiated as airborne noise. The procedure according to the invention intervenes here in that the pulse-width-modulated control signal of the metering valve is defined as a function of the driving speed of the motor vehicle. The pulse-width-modulated control signal, which is essentially determined by the NOx emissions to be removed from the internal combustion engine, is at least additionally influenced by the driving speed of the motor vehicle. The influencing is carried out in such a way that the noise of the switching process of the dosing valve, which can be heard outside, is minimized. The required intervention in the pulse width modulated drive signal is preferably determined experimentally.

Advantageous developments and refinements of the procedure according to the invention result from the dependent claims.

A first embodiment provides that the period of the pulse-width-modulated control signal is reduced as the driving speed of the motor vehicle decreases. With this measure, the frequency of the noise is lowered as the driving speed decreases and thus reaches a frequency range that is perceived as less disturbing.

A further development of this embodiment provides that the period of the pulse-width-modulated control signal is continuously reduced as the driving speed of the motor vehicle decreases. Accordingly, the period is lengthened if the driving speed decreases at the same time.

Another development of these refinements provides that the period of the pulse-width-modulated drive signal is limited to a maximum period of 1 second, for example. With this measure, the necessary reagent dosing operation can be maintained. As a result, the reagent metering is maintained even when the motor vehicle is stationary.

Another embodiment provides that the pulse duration of the pulse-width-modulated control signal is lengthened as the driving speed of the motor vehicle decreases, it being possible according to a further development that the pulse duration is continuously lengthened.

A development of these refinements provides that the pulse duration of the pulse-width-modulated drive signal is limited to a minimum pulse duration. This measure also ensures that the required reagent metering operation can be maintained.

According to one embodiment, a driving speed threshold value is provided, with the pulse-width-modulated control signal only at falling below the driving speed threshold value as a function of the driving speed of the motor vehicle. As a result, the normal dosage is only intervened below the driving speed threshold value.

The device according to the invention for carrying out the method initially relates to a specially designed control unit. As a means for carrying out the method, the control unit contains in particular a dosing signal determination and a control signal determination.

The control unit preferably contains at least one electrical memory in which the method steps are stored as a control unit program.

The control unit program according to the invention provides that all steps of the method according to the invention are carried out when it runs in a control unit.

The control unit program product according to the invention with a program code stored on a machine-readable carrier executes the method according to the invention when the program runs in a control unit.

Embodiments of the invention are shown in the drawing and explained in more detail in the following description.

character list

• 1 shows a technical environment in which a method according to the invention takes place and
• 2a and 2 B show control signals as a function of time.

Detailed description of the exemplary embodiments

1 shows a motor vehicle 10 in which an internal combustion engine 12 is provided as a drive. An air intake 16 is arranged in an intake area 14 of the internal combustion engine 12 . A reagent metering device 20 and a catalytic converter 22 are arranged in an exhaust gas region 18 of the internal combustion engine 12 . The reagent metering device 20, which includes a metering valve 24, meters a reagent into an exhaust passage 26 of the internal combustion engine 12, which reagent is required in the catalytic converter 22 in order to eliminate an undesirable exhaust gas component. In the exemplary embodiment, it is assumed that the catalytic converter 22 is implemented as an SCR catalytic converter, which converts the NOx emissions from the internal combustion engine 12 .

Air detection 16 provides a control unit 30 with an air signal ms_L. Control unit 30 provides metering valve 24 with a control signal s_DV.

The control unit 30 contains a NOx untreated emissions determination 32, which the air signal ms_L and a measure Md for the load of the internal combustion engine 12 are made available and which a calculated NOx untreated emissions ms_NOx_Sim of the internal combustion engine 12 provides.

The control unit 20 also contains a dosing signal definition 34, which is provided with the calculated NOx untreated emissions ms_NOx_Sim of the internal combustion engine 12, the temperature te_Kat of the catalytic converter 22 and other unspecified input variables and which provides a dosing signal s_Rea. The dosing signal s_Rea thus depends in particular on the raw NOx emissions of the internal combustion engine 12, with at least the temperature te_Kat of the SCR catalytic converter 22 being taken into account. The catalytic converter 22 configured as an SCR catalytic converter has a conversion efficiency that is low at low and high temperatures te_Kat and passes through a maximum in between. Furthermore, an SCR catalytic converter 22 has a reagent storage capacity which increases continuously with decreasing temperature. Ammonia, for example, is provided as the reagent and can be metered by the reagent metering device 20 directly into the exhaust gas duct 26 upstream of the SCR catalytic converter 22 . A precursor of the required reagent, for example a urea-water solution, is preferably metered.

In principle, the dosing signal s_Rea could be made available directly to the solenoid valve 24 of the reagent dosing device 20 . According to the invention, however, at least one influencing of the control signal s_DV of the solenoid valve 24 as a function of the driving speed v of the motor vehicle 10 is also provided. The driving speed v is taken into account in the control signal specification 36, which, in addition to the metering signal s_Rea, is provided with the driving speed v of the motor vehicle 10, a driving speed threshold value v_SW, a maximum period PRT_v_Max of the control signal s_DV and a minimum pulse duration PD_v_Min of the control signal s_DV and which provides the pulse width modulated drive signal s_DV. The control signal s_DV is made available to the solenoid valve 24 as part of clocked operation.

The pulse width modulated drive signal s_DV is in 2a shown for the case in which the driving speed v is greater than the driving speed threshold value v_SW, which is set to a speed of 30 km/h, for example. It is assumed here that above the driving speed threshold value v_SW the noise emission of the solenoid valve 24 is no longer disturbing.

A first pulse duration PD_N1 is specified during a first period duration PRT_N1 of the control signal s_DV. Both the first period duration PRT_N1 and the first pulse duration PD_N1 can be varied in order to convert the dosing signal s_Rea into the control signal s_DV.

After the end of the first period PRT_N1, an increased dosing requirement should occur, which is reflected in the dosing signal s_Rea. The increased dosing requirement should be present during a second period duration PRT_N2, during which the second pulse duration PD_N2 should occur. In the exemplary embodiment shown, it is assumed that the increased dosing requirement is realized both by shortening the second period PRT_N2 compared to the first period PRT_N1 and by lengthening the second pulse duration PD_N2 compared to the first pulse duration PD_N1. In principle, it is sufficient if either the second period duration PRT_N2 is shortened or the second pulse duration PD_N2 is lengthened.

The pulse width modulated drive signal s_DV is in 2 B shown for the case that the driving speed v is less than or at most equal to the driving speed threshold value v_SW. In the exemplary embodiment shown, it should be assumed that a speed-dependent definition of the pulse-width-modulated drive signal s_DV should then be provided.

Opposite the inside 2a The control signal s_DV shown should first be extended after the driving speed v has influenced the control signal s_DV in order to move the fundamental frequency of the control signal s_DV to a frequency range which is as low as possible and which is perceived as less disruptive. During a first speed-dependent period PRT_N1_Max, which in the exemplary embodiment shown is, for example, equal to the first period PD_N1 in normal dosing operation, only one speed-dependent pulse duration PD_v_Min should occur, for example.

In the embodiment shown, it is assumed that according to 2 B the maximum possible speed-dependent period PRT_v_Max, which is set to 1 second, for example, occurs as the first speed-dependent period. The limitation to a maximum possible speed-dependent period PRT_v_Max ensures that the normal metering operation can be maintained so that the SCR catalytic converter 22 can fulfill its cleaning function.

Furthermore, it is assumed in the embodiment shown that according to 2 B the minimum speed-dependent pulse duration PD_v_Min occurs within the maximum possible speed-dependent period duration PRT_v_Max. This additional measure ensures that higher frequency components of the noise emission spectrum do not occur, or at least only to a small extent.

Following the first maximum speed-dependent period PRT_v_Max, a shorter second speed-dependent period PRT_v is shown, during which only one speed-dependent pulse duration PD_v should also occur, the second speed-dependent pulse duration PD_v being longer than the minimum first speed-dependent pulse duration PD_v_Min. Both because of the shortened second speed-dependent period PRT_v and because of the additionally lengthened second speed-dependent pulse duration PD_v, a larger amount of reagent is metered during the second speed-dependent period PRT_v.

The speed-dependent intervention in the period duration PRT_v and/or the pulse duration PD_v of the pulse-width-modulated control signal s_DV, which generally leads to at least an extension of the speed-dependent period duration PRT_v at decreasing speeds, has no negative impact on the required reagent metering because at low driving speeds of the motor vehicle 10, corresponding to a low load of the internal combustion engine 12, a correspondingly lower raw NOx emission occurs, for the elimination of which a smaller amount of reagent is required than at high driving speeds v.

According to one embodiment, it can be provided that the intervention of the driving speed v in the activation signal s_DV takes place continuously, with the driving speed threshold value v_SW being provided if necessary. The continuous intervention should mean that with decreasing driving speed v the speed-dependent period PRT_v and the speed The speed-dependent pulse duration PD_v or only the speed-dependent period duration PRT_v or the speed-dependent pulse duration PD_v can be continuously lengthened accordingly. As an alternative to this, provision can be made for the engagement to take place in stages, with at least one stage being provided. In this case, too, the speed-dependent period duration PD_v and the speed-dependent pulse duration PD_v or only one of these variables can be changed in steps.

Claims (12)

Method for operating a reagent metering device (20), which meters a reagent into an exhaust duct (26) of an internal combustion engine (12) of a motor vehicle (10), in which the metered quantity is specified with an electromagnetically actuated metering valve (24) which is equipped with a pulse-width-modulated control signal (s_DV), characterized in that the pulse-width-modulated control signal (s_DV) of the metering valve (24) is determined as a function of the driving speed (v) of the motor vehicle (10), a driving speed threshold value (v_SW) being provided and that the pulse-width-modulated control signal (s_DV) is defined only when the vehicle speed falls below the threshold value (v_SW) as a function of the vehicle speed (v) of the motor vehicle (10). procedure after claim 1 , characterized in that the speed-dependent period (PRT_v) of the control signal (s_DV) is lengthened as the driving speed (v) decreases. procedure after claim 2 , characterized in that the speed-dependent period (PRT_v) of the control signal (s_DV) is continuously lengthened as the driving speed (v) decreases. procedure after claim 2 or 3 , characterized in that the speed-dependent period (PRT_v) of the control signal (s_DV) is limited to a maximum speed-dependent period (PRT_v_Max). procedure after claim 4 , characterized in that the maximum speed-dependent period (PRT_v_Max) is 1 second. procedure after claim 1 , characterized in that the speed-dependent pulse duration (PD_v) of the control signal (s_DV) is lengthened as the driving speed (v) decreases. procedure after claim 6 , characterized in that the speed-dependent pulse duration (PD_v) of the control signal (s_DV) is continuously lengthened as the driving speed (v) decreases. procedure after claim 6 or 7 , characterized in that the speed-dependent pulse duration (PD_v) of the control signal (s_DV) is limited to a minimum speed-dependent pulse duration (PD_v_Min). Device for operating a reagent dosing device, characterized in that at least one for carrying out the method according to one of Claims 1 until 8th specially prepared control unit (30) is provided. device after claim 9 , characterized in that the control unit (30) contains a dosing signal determination (34) and a control signal determination (36). Control unit program that contains all the steps of a method according to one of the Claims 1 until 8th executes when the program runs in a control unit (30). Control unit program product with a program code stored on a machine-readable carrier for carrying out the method according to one of Claims 1 until 8th , if the program is executed in a control unit (30).

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