WO2018077526A1

WO2018077526A1 - Method for achieving increased accuracy of the quantity in pressure-controlled metering systems

Info

Publication number: WO2018077526A1
Application number: PCT/EP2017/072835
Authority: WO
Inventors: Edna Boos; Matthias Burger; Marc Chaineux; Roland Waschler
Original assignee: Robert Bosch Gmbh
Priority date: 2016-10-24
Filing date: 2017-09-12
Publication date: 2018-05-03
Also published as: EP3529469A1; DE102016220795A1; KR20190068608A; CN109844276A

Abstract

The invention relates to a method for operating a pressurized metering system, comprising a conveyor module, a metering valve and a pressure sensor, wherein, during a pressure control, an adaptation of the control of the metering valve that is subject to tolerances is carried out with the aim of improving the integral accuracy of the metered quantity.

Description

Description title

Method for implementing increased quantity accuracy in pressure-controlled metering systems

The present invention is based on a method for operating a metering system, in which a pressure control is combined with an adaptation of the control of a metering valve with the aim of an improved

Quantity accuracy of the entire system. Furthermore, the present invention relates to a computer program that performs each step of the method when running on a computing device, as well as a machine-readable one

Storage medium storing the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method.

State of the art

Pressure-controlled metering systems are generally based on the principle that a pump provides a desired system pressure and regulates to the narrowest possible range around a defined setpoint, and a

Dosing, typically a metering valve based on this pressure by setting a matching valve opening time the desired amount. In such systems, the metered quantity accuracy depends essentially on the tolerance of the metering valve.

Alternatively, one makes in so-called "volumetric systems" without return the ia high accuracy of the (reciprocating) pump and the property that in the stationary state, the very well-known, funded by the pump quantity also leaves the system as dosed amount again, This is thanks to the principle of volumetry in combination with the

comparatively small quantity tolerances of the reciprocating pump on average a high quantity accuracy. Concerning. However, the pressure exists here in In general, no closed loop, rather, the system pressure is a function of the pilot control and the tolerances of the pump and the metering valve and is not readjusted, which is usually too

comparatively large tolerances in self-adjusting system pressure leads. Thus, prior art is a high pressure stability at relatively high

Dosing quantity tolerance in pressure-controlled systems or improved

Dosing quantity tolerance at the expense of higher pressure fluctuations in purely pilot-operated "volumetric systems." There are also methods and apparatus for operating a

Internal combustion engine, in particular in motor vehicles, in whose exhaust gas line an S CR catalyst (Selective Catalytic Reduction) is arranged, which reduces the nitrogen oxides (NOx) contained in the exhaust of the internal combustion engine in the presence of a reducing agent to nitrogen. As a result, the proportion of nitrogen oxides in the exhaust gas can be significantly reduced. For the course of the

Reaction requires ammonia (N H3). As reactants, N H3-releasing reagents are used, which are added to the exhaust gas. As a rule, an aqueous urea solution is used for this, which is injected into the exhaust gas line upstream of the S CR catalyst.

For the promotion and dosage of the reducing agent solution from a

Reducing agent tank is generally provided a hydraulic metering system comprising a feed pump, a pressure line, a metering module, with at least one metering valve, and the required sensors and an electronic control device. The feed pump promotes the

Reducing agent solution from the reducing agent tank via the pressure line in the dosing. For the appropriate dosage, the required or desired dosage of the reducing agent solution over the or

Dosing valve (s) metered into the exhaust system.

The metering valve is opened when it is activated, ie when an electric current is applied for control. It is kept open for a fixed drive time, so that reducing agent is injected into the exhaust system. If the metering valve is no longer activated, ie no current is applied, the metering valve closes again. The driving time and in the Pressure line and thus also prevailing in the metering pressure, in addition to the geometry of the spray orifice plate, the essential factors that determine the metered amount. It should be noted that the dosing valve does not react directly to the activation. As a result, an indefinite mass of the reducing agent solution escapes uncontrollably into the

Exhaust system. The actually metered in reducing agent solution thus deviates from the actual reducing agent mass, so that the metering valve is heavily toleranced.

In DE 10 2010 031 655 AI a method for operating a pressure-controlled metering system for a S CR catalyst is described. A pressure regulator regulates the pressure in the SCR system by adjusting the control of the feed pump according to the current requirements for the opening time of the metering valve. The aim of this regulation is to adapt the prevailing, actual pressure to a desired pressure. The method described herein is characterized in that an adaptive

Feedforward control is used for the control. In adaptive pilot control, the control signal of the feed pump motor is at different

The teachings of the dosing valve are taught. As soon as the adaptive feedforward controller has learned two or more points, it is used to determine the necessary next actuating signal of the feed pump motor. Next to the

Feed pump motor, other actuators of the metering system can be used as a control signal, but the feed pump motor provides a very accurate signal. As a result, high pressure overshoots and undershoots associated with large dosing quantity changes as well as associated long control times are avoided, thus optimizing the control quality.

DISCLOSURE OF THE INVENTION The invention relates to a method for operating pressurized

Dosing systems, which comprise a delivery module, with a generally low tolerance, a typically more tolerantbehältetets metering valve, a pressure module connecting the delivery module and the metering valve and arranged between the delivery module and the metering pressure sensor. It should be noted that in this SCR system no return is provided and therefore the metering system, if not injected, represents a closed system- and no reducing agent solution can escape. While a pressure control is performed in the metering system, an adaptation of the control of the tolerance-loaded metering valve takes place. The result is that the advantages of a pressure-controlled system, namely the low tolerance of the pressure during metering, and the advantages of a volumetric system, namely the integrally low tolerance of the delivered and then metered amount are combined, to a total of lower Total tolerance during dosing.

Preferably, the adaptation of the control of the metering valve can be carried out by means of an adaptation factor. The adaptation factor depends on an integral quantity conveyed by the delivery module and on a nominal amount metered in by the metering valve, and can in particular be calculated as a quotient of the delivered quantity and the nominal metered quantity for a specific period of time. By calculating the

Adaptation factor can be quantized a deviation of the actually metered by the metering amount of a nominal amount and this deviation can be corrected by adapting the control of the metering valve by means of the adaptation factor. In addition, in volumetric metering systems, a high accuracy of the metered amount can be achieved in an integral manner, since the complete pumped and generally low tolerance amount is completely metered in because of the absence of return. Here, the high accuracy of the conveyor module is used in order to obtain a high accuracy - and thus a low tolerance - of the conveyed quantity. As an example, a reciprocating pump to serve in the delivery module, the one at each stroke by the volume of the reciprocating piston

promotes given amount.

By adapting the metering valve, its activation duration can preferably be adapted. In order to calculate the activation duration, in particular the valve flow characteristic can be corrected by means of the adaptation factor. This offers a possibility, on the basis of the deviations, to carry out a quantized adaptation of the control of the metering valve.

Preferably, the delivery module with pressure sensor and the pressure line as a controlled system with the prevailing system pressure as a control variable form a closed loop, via which the pressure control can be made. In the course of this regulation, a desired pressure to be established by the delivery module is compared with an actual pressure prevailing in the delivery conduit. On the basis of that will

Conveyor module, e.g. via a two-position controller, so controlled that the actual pressure adapts to the desired pressure. As a result, a pressure-controlled system is obtained. In pressure-controlled systems, a high accuracy of the pressure prevailing in the dosing system is achieved. The pressure built up by the delivery module can not be reduced due to the absence of return and remains constant until dosing.

The computer program is set up to perform each step of the method, in particular when it is performed on a computing device or controller. It allows the implementation of the method in a conventional electronic control unit without having to make any structural changes. For this it is on the machine-readable

Storage medium stored.

By putting the computer program on a conventional

electronic control unit, the inventive electronic

Control unit, which is adapted to adapt the opening duration.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

Figure 1 shows an SCR system that can be operated by means of an embodiment of the method according to the invention. FIG. 2 shows a flow diagram of an embodiment of the invention

inventive method.

FIG. 3 shows a diagram of a standardized reducing agent flow rate over a system pressure, which tolerances are governed purely volumetrically

Dosing system, for a purely pressure-controlled dosing system and for a regulated according to an embodiment of the method according to the invention shows system. Embodiment of the invention

The invention is described below using the example of a metering system in the form of an SCR system (Selective Catalytic Reduction). FIG. 1 shows an SCR system 10 for delivering reducing agent through a

Pressure line 11 in a SCR catalyst, not shown. It comprises a delivery module 12, which comprises a delivery pump 13, which is set up to deliver reduction agent from a reduction agent tank 14. In this embodiment, the feed pump 13 is designed as a reciprocating pump. The delivery module 12 is connected via the pressure line 11 with a metering module 15, wherein reducing agent is conveyed by the delivery module 12 through the pressure line 11 to the metering module 15, where it then by a

Metering valve 16 is metered into an exhaust line, not shown. Furthermore, the pressure line 11 has a pressure sensor 17 which measures an actual pressure p _ta t in the pressure line 11. The pressure sensor 17 and the delivery module 12 are connected to an electronic control unit 18 and form a common control loop. Based on a from the

Pressure sensor 17 measured actual pressure p _ta t and a desired pressure Pgew controls the electronic control unit 18 by means of a pressure control, the feed pump 13. The electronic control unit 18 is also with the

Dosing module 15 and connected to the metering valve 16 and can control this. The adaptation of the control of the metering valve 16 takes place within the electronic control unit 18. It should be noted here that no return into the reducing agent tank 14 is provided in this metering system, so that the delivery module 12, the pressure line 11 and the metering module 15 a form a closed system. A built-up by the delivery module 13 pressure p remains constant until dosing. Likewise, the sponsored

Reductant amount does not otherwise flow back and is the

Metering completely metered via the metering valve 16 in the exhaust line.

FIG. 2 shows a flow diagram of an embodiment of the invention

inventive method. At the beginning, the actual pressure p _ta t is measured by the pressure sensor 17. According to the embodiment, a pressure control 30 follows, at which first a pressure difference Δρ is calculated 31 from the actual pressure ptat and the desired pressure p _gew . The

Pressure difference Δρ then passes through a filter 32, in which undesirable

Interference signals are removed. As filter 32, a low-pass filter will be used which suppresses high-frequency signal components resulting from measurement noise or high-frequency pressure oscillations. Following the filtered pressure difference Δρ 'passes ι _(a two-point controller 33. If the filtered pressure difference Δρηκ below a threshold p _s, in other words, the feed pump 13 are the actual pressure p _ta t and the desired pressure p _gew, is close to each other is not actuated 34 and there is no hub. however, If the filtered pressure difference Δρηκ above the threshold p _s, in other words, are the actual pressure p _ta t and the desired pressure p _wt far apart, the feed pump in accordance with a pump frequency f _p is adjusted 35 so that In this case, the actual pressure p _ta t adapts to the desired pressure Pgew

Reducing agent mass m _p easily determined 36. In the case of the reciprocating pump, the reductant mass delivered per stroke is determined by the volume of the piston. In order to determine the integrally conveyed reducing agent mass m _p , the reducing agent mass delivered per stroke is combined with one via a

Measurement period executed number of strokes multiplied.

During the pressure control 30, an adaptation 40 of the control metering valve 16 takes place, which is based on the volumetric principle of the underlying metering system. It is exploited that the integrally promoted reducing agent mass m _{p is} completely metered through the metering valve 16. From a desired reducing agent mass m _ge w is by means of

electronic control unit 18 determines a nominally metered mass m _n 41. The nominal metered reducing agent mass m _n is a supposedly integrally metered reducing agent mass of a nominal metering valve. By definition, the nominal metering valve is tolerance-free with respect to the reducing agent mass metered in by it. Consequently, the nominally metered reducing agent mass m _{n is} only dependent on the actual pressure p _ta t and thus has a very low tolerance after the pressure control 30. From the nominally metered reducing agent mass m _n and the integrally conveyed reducing agent mass m _p , a quotient is calculated according to formula 1 over the measuring period 42: dov- _m (formula 1)

This quotient is called adaptation factor aov and gives a

Deviation between the actually metered reducing agent mass and the nominal metered reducing agent mass m _n . In an ideal

Dosing system without tolerances results in the adaptation factor aov therefore to one. The adaptation factor aov is used in the following for an

electronic control unit 18 to correct nominal valve flow characteristic Q _n 43 to obtain an adapted valve flow characteristic Qad according to formula 2:

Qad - Qn ^'a DV (Formula 2)

In the adapted valve flow characteristic Q _a d, therefore, the deviation between the actually metered reducing agent mass and the nominally metered reducing agent mass m _{n is} taken into account. An adjustment is carried out 44 of a required Ventilansteuerdauer _a t on the basis of these adapted valve flow characteristic Q _a d. As a result, Ventilansteuerdauer t is _a function of the adaptation factor 44. aov and thus adjusted by the integrally supported reducing agent mass m _p and the nominal metered reducing agent mass m _n Thus, the metering valve 16 after the adjustment 44 of the Ventilansteuerdauer t _a a significantly reduced stationary mass tolerance.

The method is illustrated by the following example. The metering valve 16 should, for example due to manufacturing tolerances and / or aging effects, Add 10% excess reducing agent. As a result, the

Feed pump 13 in comparison to a desired reducing agent rrigew mass to 10% too high integrally supported reducing agent mass m _p to assist in pressure control 30 the actual pressure p _ta t at the desired pressure p adapt _wt. The nominally metered reducing agent mass m _n is determined by the electronic control unit 18 41 so that it corresponds to the desired reducing agent mass m _ge w at prevailing, actual pressure p _ta t. The calculation 42 of the adaptation factor aov according to formula 1 results as follows:

_M 0% ₌ (Fromel l ') D ^V 100%

The activation period t _a must then compared to a nominal

Control duration shortened by the reciprocal of the adaptation factor aov to compensate for the positive mass tolerance of the metering valve 16. The

1

Driving time is therefore shortened by 1 «9%.

1, 1

FIG. 3 shows a diagram of a standardized reducing agent mass flow rate R, above the system pressure p. There are shown a nominal 50, a maximum 51 and a minimum 52 course for the feed pump. The mass tolerance of

Feed pump 13 can be read as the difference between the maximum curve 51 and the minimum curve 52. Similarly, a nominal 60, a maximum 61 and a minimum 62 course for the metering valve 16 are shown. Similarly, the pressure tolerance and the mass tolerance of the metering valve 16 can be read out as the difference between the maximum course 61 and the minimum course 62. From the nominal curve 60, the nominal metered

Reducing agent mass m _{n are determined} for the respective actual pressure p _ta t. Furthermore, the diagram from FIG. 3 shows a total tolerance 70 of a volumetric metering system operated purely pilot-operated, a total tolerance 80 of a purely pressure-controlled metering system and a total tolerance 90 of a metering system regulated according to an exemplary embodiment of the method according to the invention. The total tolerance 70 of the purely pilot-operated, volumetric metering system results from the tolerance of Feed pump 13 and the tolerance of the metering valve 16. The total tolerance 80 of the purely pressure-controlled metering system, however, is essentially only dependent on the quantity tolerance of the metering valve 16. In the total tolerance 90 of the regulated according to the embodiment of the method according to the invention metering system, the low pressure tolerance of the pressure-controlled

Dosing system combined with the reduced mass tolerance of the volumetrically controlled dosing system. Therefore, it is relatively small compared to the other two total tolerances 70 and 80. Above all, the mass tolerance is reduced by the method according to the invention, which is represented in the diagram by the symbolized as arrows projection of the total tolerances 70, 80 and 90 to the normalized reducing agent mass flow rate R _m .

Claims

claims

1. A method for operating a pressurized metering system (10), which comprises a delivery module (12), a metering valve (16) and a

Pressure sensor (17), characterized in that, while ei pressure control (30) is carried out, an adaptation (40) of the control of the tolerance-sensitive metering valve (16).

2. The method according to claim 1, characterized in that the Adapti (40) of the control of the metering valve (16) by means of a

Adaptation factor (aov), which depends on an amount (m _p ) delivered by the delivery module (12) and a nominal amount (m _n ) metered in by the metering valve (16).

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

Adaptation factor (aov) for a fixed period as a quotient of the integrally funded amount (m _p ) and the integral, nominally metered amount (m _n ) is calculated (42).

4. The method according to any one of the preceding claims, characterized

characterized in that by the adaptation (40) a control period (t _a ) of the metering valve (16) adapted (44).

5. The method according to claim 4, characterized in that a

Valve flow characteristic (Q _a d) by means of the adaptation factor (aov) is corrected (43) to calculate the driving time (t _a ).

6. The method according to any one of the preceding claims, characterized

characterized in that the pressure control (30) by means of a

closed loop for the delivery module (12) and the Pressure sensor (17) is made.

7. The method according to claim 6, characterized in that the

Pressure control (30) by a two-position controller (33) is performed, which controls the conveyor module (13) (34, 35).

8. Computer program which is set up every step of the

Method according to one of claims 1 to 7 perform.

9. Machine-readable storage medium on which a

Computer program according to claim 8 is stored.

10. Electronic control device (18) which is adapted to operate by means of the method according to one of claims 1 to 7, the dosing system (10).