DE102011076955B4 - Method for diagnosing a dosing system and device for carrying out the method - Google Patents

Abstract

Method for diagnosing a dosing system which doses a reagent (12) into the exhaust duct of an internal combustion engine, in which the reagent (12) stored in a tank (10) is brought to an operating pressure (p0) by a pump (14) at which a return line (24) of the reagent (12) from the pump (14) is provided, in which a flow rate is set with an electrically controlled metering valve (16) and in which the pressure (p) of the reagent (12) between the pump ( 14) and the metering valve (16) is measured, in which the return (24) of the reagent (12) can be specified variably by means of an electrically controlled throttle (26), at which the pressure (p) of the reagent (12) is set to a diagnostic start pressure (pD) is brought, at which the throttle (26) is closed and thus the return (24) is prevented, at which a diagnostic metering rate is set at which the pump (14) is switched off, and at which the measured pressure drop (40 , 42, 44, 50, 52, 54) is checked, - whether the pressure drop (40, 42, 44, 50, 52, 54) is outside a tolerance band (48) or is checked, - whether the pressure drop (40, 42, 44, 50, 52, 54) is above an upper limit value or a check is carried out to determine whether the pressure drop (40, 42, 44, 50, 52, 54) is below a lower limit value and at which, if a tolerance band is determined, or an error signal (F) is provided if the limit value is exceeded, characterized in that the tolerance band (48) or the at least one limit value are defined as a function of the diagnostic metering rate.

Description

The invention is based on a method for the diagnosis of a dosing system, which doses a reagent in the exhaust passage of an internal combustion engine and of a device for carrying out the method according to the preamble of the independent claims.

The subject matter of the present invention is also a computer program and a computer program product.

State of the art

In the published patent application DE 10 2005 001 119 A1 a diagnosis of metering valves is provided, which are used in an arrangement which doses fuel as a reagent in the exhaust gas region of an internal combustion engine. The oxidizable hydrocarbons are provided for heating an exhaust gas treatment device. The diagnostic provides monitoring of reagent pressure that occurs between a reagent safety valve and a reagent metering valve. The reagent pressure is detected during different switching states of the reagent safety valve and the reagent metering valve. A diagnostic step provides that the reagent is brought to a predetermined reagent target pressure. Thereafter, it is checked with closed valves, whether the reagent pressure drop does not exceed a predetermined pressure gradient.

In the published patent application DE 10 2004 061 247 A1 a comprehensive diagnosis of metering valves is provided, which are used in an arrangement which also doses fuel as a reagent in the exhaust region of an internal combustion engine. The reagent pressure occurring in the reagent path between a reagent safety valve and a reagent metering valve is detected at different switching states of the valves. A diagnostic step also provides here that after closing the valves, it is checked whether a reagent pressure drop occurs, which is evaluated with regard to whether the pressure drop does not exceed a predetermined pressure gradient.

In the published patent application DE 103 60 891 A1 a diagnostic method of a metering valve is described, which is set to a certain flow rate of a metered into an exhaust region of an internal combustion engine reagent. The metering valve is supplied with the reagent brought by a pump to a predetermined pressure reagent, wherein the pressure is detected by a pressure sensor. The diagnostic provides an assessment of a measure of the flow rate during a diagnostic time. After the occurrence of a diagnostic start signal, the metering valve is closed and the reagent is brought by means of a pump to a predetermined diagnostic start pressure. Subsequently, the metering valve is set to a predetermined flow rate and the occurring during the diagnostic time pressure difference evaluated. A first embodiment provides that the diagnosis time is fixed and that errors are detected when the pressure difference during the fixed diagnosis time exceeds a predetermined pressure difference limit value. Alternatively it can be provided that the pressure difference is fixed and that errors are detected when the diagnosis time exceeds a predetermined diagnostic time limit. The reagent pressure which a pressure sensor detects is evaluated.

In the published patent application DE 10 2008 005 989 A1 a method for diagnosing a metering valve of an exhaust aftertreatment device is described, which also doses a reagent in the exhaust region of an internal combustion engine, wherein the reagent is brought from a pump to a metering pressure, wherein the diagnosis is made on the basis of an assessment of the pressure drop of the reagent. The pressure drop is evaluated when the pump is switched off and continued dosing, whereby the leakage of a bypass valve bypassing the pump is taken into account. The bypass valve is by design part of the pump.

In the published patent application EP 2 131 021 A1 describes a method for diagnosing a dosing system, which doses a reagent in the exhaust passage of an internal combustion engine. The stored in a tank reagent is brought to an operating pressure, wherein the pressure between the pump and an electrically controlled metering valve is measured. There is a return, which has an electrically controlled throttle. At the beginning of the diagnosis, the pressure is brought to a diagnostic start pressure, the return throttle is closed, a diagnostic dosing rate is set with the dosing valve and then the pump is switched off. The subsequent pressure drop is then checked to see if it is outside a tolerance band.

In the published patent application DE 10 2009 000 097 A1 a conveyor for an SCR system for injecting a reagent into an exhaust system of an internal combustion engine is described. From the outlet of the pump branches off a return line, which returns to the storage tank of the reagent. In the return line a flow restrictor is arranged.

In the published patent application DE 10 2006 012 855 A1 an arrangement is described, which in the published patent application DE 10 2009 000 097 A1 corresponds structure described, but in the return line, a variable controllable throttle is provided.

The invention has for its object to provide a method for diagnosing a metering device with a return line which doses a reagent in the exhaust passage of an internal combustion engine, and an apparatus for performing the method, which allow a simple diagnosis reliable diagnosis.

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

Disclosure of the invention

The method according to the invention for diagnosing a metering system assumes that a reagent is metered into the exhaust region of an internal combustion engine, that the reagent stored in a tank is brought to an operating pressure by a pump, that a return of the reagent is provided by the pump a flow rate is adjusted with an electrically controlled metering valve and that the pressure of the reagent between the pump and the metering valve is measured. Furthermore, the method according to the invention is based on the fact that the return of the reagent from the pump by means of an electrically controlled throttle is variably predetermined, that the pressure of the reagent is brought to a diagnostic starting pressure, that the throttle is closed and thus the return is prevented that a Diagnosedososierrate is set to switch off the pump, then check the measured pressure drop to see if the pressure drop is outside a tolerance band or to check if the pressure drop is above an upper limit or to check if the pressure drop is below a lower limit and that an error signal is provided when a tolerance band or limit is exceeded.

The procedure according to the invention is characterized in that the tolerance band or the at least one limit value is established as a function of the diagnostic dosing rate.

The procedure according to the invention makes it possible to diagnose a specially constructed metering system in which a return path from the outlet of the pump, at which the pressure to be diagnosed occurs, leads to the tank of the reagent, which is set to a predetermined return flow rate with an electrically controlled throttle and, in particular, completely closed can.

A specification of the tolerance band with an upper and lower limit value makes it possible to diagnose whether the pressure drop is too slow or too fast in a diagnostic step. Setting an upper limit allows diagnosing whether the pressure drop is too slow, and setting a lower limit allows diagnosing whether the pressure drop is too fast.

In particular, the determination of the tolerance band or of the at least one limit value as a function of the dosing rate makes it possible to optimize the diagnosis with regard to the achievable sensitivity or with regard to the duration of the diagnosis.

Advantageous developments and refinements of the procedure according to the invention will become apparent from the dependent claims.

The device according to the invention for carrying out the method initially relates to a specially prepared control device which contains means for carrying out the method.

The control unit preferably contains at least one electrical memory in which the method steps are stored as a control unit program. The controller includes a pressure drop rating for comparing the measured pressure with a predetermined tolerance band or at least one predetermined threshold.

Brief description of the figures

1 shows a part of a dosing system in which a method according to the invention runs and

2 shows pressure gradients as a function of time, which can occur in the dosing system.

Detailed description of the embodiments

1 shows a part of a dosing system, the one in a tank 10 stored reagent 12 with a pump 14 to a predetermined operating pressure p0 brings and a metering valve 16 for metering in the not shown exhaust passage of an internal combustion engine is available.

As a reagent 12 For example, a urea-water solution is provided which serves as a raw material for the production of ammonia, which is used to reduce nitrogen oxides contained in the exhaust gas of the internal combustion engine in an SCR. Catalyst (selective-reduction catalyst) is used.

The pump 14 is powered by an electric motor 18 driven, which is driven by a pump control signal S1 in the context of preferably a clocked operation in which the operating voltage is provided with a predetermined period and within the period with a predetermined pulse / pause ratio. The pump control signal S1 represents a control unit 20 ready. The pump control signal S1 depends, in particular, on the required metering rate to which the metering valve 16 is set at the operating pressure p0 with a Dosierventilsteuersignal S2, which is also the controller 20 provides.

The pump 14 provides one of a pressure sensor in response to the pump control signal S1 22 measured pressure p ready. The pressure p becomes not only dependent on the pump control signal S1 but also on a return path 24 for the reagent 12 regulated. This is in the return path 24 a throttle 26 provided with adjustable cross-section. The throttle 26 is driven by a throttle control signal S3. It is essential here that the cross section of the throttle 26 can be changed down to zero, allowing complete closing of the return path 24 is possible. In the embodiment shown is of an internal return path 24 went out. In principle, but also a return 24 be provided, the back up in the tank 10 leads.

The pressure p of the reagent 12 controls the controller 20 Therefore, on the one hand by the specification of the pump control signal S1 and on the other hand by the specification of the throttle control signal S3 to the operating pressure p0, the setpoint p0 the control unit 20 is made available.

The diagnosis is started with a diagnostic signal S4. Preferably, the diagnosis is performed when at least approximately a stationary operating state of the internal combustion engine is present, so that the metering rate is at least approximately constant.

When the diagnostic signal S4 occurs, the diagnosis is started by the control unit 20 a predetermined diagnostic start pressure pD which controls the control unit 20 is made available. The diagnostic start pressure pD may correspond to the normal operating pressure p0 outside the diagnostic mode, so that no special pressure for the diagnosis needs to be set. After adjusting the diagnosis start pressure pD, the throttle control signal S3 is used to completely close the throttle 26 causes.

The diagnosis can be carried out at different dosing rates. Therefore, the controller 20 a diagnostic dosing rate signal 28 provided with the Dosierventilsteuersignal S2 to the metering valve 16 is passed on. The diagnosis dosing rate may correspond to a dosing rate occurring outside of the diagnostic operation, for example the last-specified dosing rate.

In 2 are pressure drops 40 . 42 . 44 as a function of time t, which may occur at different states of the dosing system. It is based on a low dosing rate, so that a sensitive diagnosis can be made, in which small deviations from a proper system can be diagnosed. It is assumed that the first pressure curve 40 corresponds to a system that is in order.

The starting point is the diagnostic start pressure pD, which occurs at a first time t0. The pressure drop is checked 40 . 42 . 44 that closed throttle 26 and at a controlled with the predetermined small Dosage Dosage metering valve 16 ,

One in the control unit 20 included pressure drop rating 46 determined as a measure of the pressure drop 40 . 42 . 44 For example, the pressure drop gradient dt / dt, which is approximated by the pressure drop difference quotient. For this purpose, the time difference t2-t1 occurring during a predetermined pressure difference p1-p2 is measured. The pressure difference p1-p2 must be within a range which is at least passed through in the case of a proper dosing system.

Alternatively or in addition to the pressure drop gradient dp / dt, the pressure drop rating 46 determine and evaluate the end pressure pE occurring at a certain point in time t3.

The pressure drop rating 46 checks whether the pressure drop gradient dp / dt and / or the final pressure pE outside a tolerance band 48 is, where for the pressure drop gradient dp / dt and for the final pressure pE at a certain time t3 different tolerance bands are to be specified. That in the 2 and 3 shown tolerance band 48 refers in each case to the evaluation of the final pressure pE at the fixed time t3.

The tolerance band 48 is an area with a lower and upper limit. This can be determined in a diagnostic process, if the pressure drop 40 . 42 . 44 exceeded the upper limit or has fallen below the lower limit.

If the at least one limit value is provided, at least one specific diagnosis can be carried out. When the pressure drop 40 . 42 . 44 exceeds the upper limit, which is higher than the upper limit, becomes too slow a pressure drop 42 diagnosed. When the pressure drop 40 . 42 . 44 exceeds the lower limit, therefore lower than the lower limit, too fast a pressure drop 44 diagnosed.

In these, on the basis of the tolerance band 48 or the fault conditions diagnosed at least one threshold, the error signal F is provided which can be displayed and / or stored.

In 2 corresponds to the second pressure drop 42 a metering system which has too low a metering rate, wherein the pressure drop 42 is too slow. This error may be due to a jamming metering valve 16 in partially closed state. The third pressure drop 44 on the other hand corresponds to a dosing system with too rapid pressure drop 44 pointing at an open-clamping metering valve 16 or indicates a leak in the dosing system.

3 shows occurring pressure drops 50 . 52 . 54 that occur at a higher diagnostic dosing rate. The advantage of a higher diagnostic dosing rate is that the diagnostic time t is low, so that the normal dosing operation is not interrupted for a long time.

In the 3 shown pressure drops 50 . 52 . 54 again assume that the fourth pressure drop 50 corresponds to a proper dosing system, while the fifth pressure drop 52 as too slow and the sixth pressure drop 54 be diagnosed as too fast, with the results corresponding to those obtained at a lower diagnostic dose rate 2 occur.

The diagnosis can thus be optimized in an advantageous manner with regard to the sensitivity or the time required. It is essential that the tolerance band 48 or the individual concrete limit value for the expected pressure drop 40 . 42 . 44 . 50 . 52 . 54 can be adapted to the respective predetermined diagnostic dosage.

Claims (8)

Method for diagnosing a dosing system which contains a reagent ( 12 ) metered into the exhaust passage of an internal combustion engine, in which the in a tank ( 10 ) stored reagent ( 12 ) from a pump ( 14 ) is brought to an operating pressure (p0), in which a return ( 24 ) of the reagent ( 12 ) from the pump ( 14 ) is provided, in which with an electrically controlled metering valve ( 16 ) a flow rate is set and at which the pressure (p) of the reagent ( 12 ) between the pump ( 14 ) and the metering valve ( 16 ), in which the return ( 24 ) of the reagent ( 12 ) by means of an electrically controlled throttle ( 26 ) is variable, in which the pressure (p) of the reagent ( 12 ) is brought to a diagnostic starting pressure (pD), in which the throttle ( 26 ) and thus the return ( 24 ) at which a diagnostic dosing rate is set at which the pump ( 14 ) and then the measured pressure drop ( 40 . 42 . 44 . 50 . 52 . 54 ) is checked - whether the pressure drop ( 40 . 42 . 44 . 50 . 52 . 54 ) outside a tolerance band ( 48 ) or is subsequently checked, - whether the pressure drop ( 40 . 42 . 44 . 50 . 52 . 54 ) is above an upper limit or is checked thereafter, - whether the pressure drop ( 40 . 42 . 44 . 50 . 52 . 54 ) is below a lower limit value and in which an error signal (F) is provided when a tolerance band or limit value is exceeded, characterized in that the tolerance band ( 48 ) or the at least one limit value is established as a function of the diagnostic dosage rate. Method according to claim 1, characterized in that as a measure of the pressure drop ( 40 . 42 . 44 . 50 . 52 . 54 ) the pressure drop gradient (dp / dt) is determined. A method according to claim 1, characterized in that as a measure of the pressure drop ( 40 . 42 . 44 . 50 . 52 . 54 ) of a predetermined time (t3) measured final pressure (pE) is determined. A method according to claim 1, characterized in that the diagnosis is started following an operating state of the internal combustion engine in which a constant metering rate has occurred. Method according to claim 1, characterized in that the metering valve ( 16 ) is driven with a pulse width modulated dosing signal and that the diagnosis dosing is set with a certain duty cycle and a certain period of the pulse width modulated Dosierventilsteuersignals (S2). Device for diagnosing a dosing device which contains a reagent ( 12 ) metered into the exhaust gas region of an internal combustion engine, characterized in that at least one for implementing the method according to one of the preceding claims specially prepared control device ( 20 ) is provided. Device according to claim 6, characterized in that the control device ( 20 ) a pressure drop determination ( 46 ) for comparing the pressure drop ( 40 . 42 . 44 . 50 . 52 . 54 ) with the tolerance range ( 48 ) or the at least one limit value. A computer program product comprising program code stored on a machine-readable medium for performing the method of any one of claims 1 to 5 when the program is run on a computer.

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