Method for operating a system with a plurality of metering valves

Abstract

The invention proposes a method for operating a metering system (32) with a plurality of metering valves (34, 35) for an SCR catalyst system, in which opening times for the injection of reducing agent are calculated for the metering valves (34, 35) based on a metering amount requirement. In the calculations of the opening times, a metering-valve-specific adaptation factor is used, w herein a deviation (Δp) of a system pressure (p.sub.ist) in the metering system (32) from a target pressure (p.sub.soll) and a weighting factor are used for calculation of the metering-valve-specific adaptation factor. The weighting factor depends on a proportion (r.sub.34, r.sub.35) of the required metering amount ((formula (I)), (formula (II)) of the respective metering valve (34,35) in relation to a total metering amount ((formula (I)), (formula (II)) of all metering valves (34, 35).

Claims

1. A method for operating a metering system (32) with multiple metering valves (34, 35) for an SCR catalytic converter system in which opening times for the injection of reducing agents are calculated for the metering valves (34, 35) on the basis of a metering quantity requirement, the method comprising: calculating the respective opening time of each of the metering valves (34, 35) based on a respective metering valve-individual adaptation factor (a.sub.34, a.sub.35), calculating the metering valve-individual adaptation factor for each of the metering valves (34, 35) when a pressure deviation (Δp) of a system pressure (p.sub.ist) in the metering system (32) from a nominal pressure (p.sub.soll) is outside a given range by using a weighting factor, the weighting factor being based on a proportion (r.sub.34, r.sub.35) of the required metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) of a total metering quantity (m.sub.34+m.sub.35) of all the metering valves (34, 35), and operating a pump and operating the metering valves (34, 35) of the metering system (32) at the respective opening times to provide the reducing agents to the SCR catalytic converter system.

2. The method as claimed in claim 1, wherein the method includes continuously calculating (63, 73) the respective metering valve-individual adaptation factor (a.sub.34, a.sub.35) for each of the metering valves (34, 35).

3. The method as claimed in claim 1, wherein the weighting factor is based on an average of the requested metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) applied against a total metering quantity (m.sub.34+m.sub.35) of all metering valves (34, 35) of a specified time interval before a current metering quantity requirement.

4. The method as claimed in claim 1, wherein the weighting factor (b, b) is based on a square of the respective proportion (r.sub.34, r.sub.35) of the required metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) of the total metering quantity (m.sub.34+m.sub.35) of all the metering valves (34, 35).

5. The method as claimed in claim 1, wherein each metering valve-individual adaptation factor (a.sub.34, a.sub.35) is calculated by an individual PI controller provided for each of the metering valves (34, 35).

6. The method as claimed in claim 5, wherein all integrators of the PI controllers are event-based.

7. The method as claimed in claim 1, further comprising calculating an adaptation factor for the stored flow volume of the pump by means of a further PI controller and based on the deviation (Δp).

8. The method as claimed in claim 1, further comprising setting the adaptation factors to 1.0.

9. A non-transitory, computer-readable medium containing instructions that when executed by a computer cause the computer to operate a metering system (32) with multiple metering valves (34, 35) for an SCR catalytic converter system in which opening times for the injection of reducing agents are calculated for the metering valves (34, 35) on the basis of a metering quantity requirement, by calculating the respective opening time of each of the metering valves (34, 35) based on a respective metering valve-individual adaptation factor (a.sub.34, a.sub.35), calculating the metering valve-individual adaptation factor for each of the metering valves (34, 35) when a pressure deviation (Δp) of a system pressure (p.sub.ist) in the metering system (32) from a nominal pressure (p.sub.soll) is outside a given range by using a weighting factor, the weighting factor being based on a proportion (r.sub.34, r.sub.35) of the required metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) of a total metering quantity (m.sub.34+m.sub.35) of all the metering valves (34, 35), and operating a pump and operating the metering valves (34, 35) of the metering system (32) at the respective opening times to provide the reducing agents to the SCR catalytic converter system.

10. The non-transitory, computer-readable medium as claimed in claim 9, wherein the weighting factor is based on an average of the requested metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) applied against a total metering quantity (m.sub.34+m.sub.35) of all metering valves (34, 35) of a specified time interval before a current metering quantity requirement.

11. The non-transitory, computer-readable medium as claimed in claim 9, wherein the weighting factor (b, b) is based on a square of the respective proportion (r.sub.34, r.sub.35) of the required metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) of the total metering quantity (m.sub.34+m.sub.35) of all the metering valves (34, 35).

12. An electronic control unit (40) configured to operate a metering system (32) with multiple metering valves (34, 35) for an SCR catalytic converter system in which opening times for the injection of reducing agents are calculated for the metering valves (34, 35) on the basis of a metering quantity requirement, by: calculating the respective opening time of each of the metering valves (34, 35) based on a respective metering valve-individual adaptation factor (a.sub.34, a.sub.35), calculating the metering valve-individual adaptation factor for each of the metering valves (34, 35) when a pressure deviation (Δp) of a system pressure (p.sub.ist) in the metering system (32) from a nominal pressure (p.sub.soll) is outside a given range by using a weighting factor, wherein the weighting factor is based on a proportion (r.sub.34, r.sub.35) of the required metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) of a total metering quantity (m.sub.34+m.sub.35) of all the metering valves (34, 35), and operating a pump and operating the metering valves (34, 35) at the respective opening times to provide the reducing agents to the SCR catalytic converter system.

13. The electronic control unit (40) as claimed in claim 12, wherein the weighting factor is based on an average of the requested metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) applied against a total metering quantity (m.sub.34+m.sub.35) of all metering valves (34, 35) of a specified time interval before a current metering quantity requirement.

14. The electronic control unit (40) as claimed in claim 12, wherein the weighting factor (b, b) is based on a square of the respective proportion (r.sub.34, r.sub.35) of the required metering quantity (m.sub.34, m.sub.35) of the respective metering valve (34, 35) of the total metering quantity (m.sub.34+m.sub.35) of all the metering valves (34, 35).

15. The electronic control unit (40) as claimed in claim 12, wherein each metering valve-individual adaptation factor (a.sub.34, a.sub.35) is calculated by an individual a PI controller provided for each of the metering valves (34, 35).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are presented in the drawings and are explained in more detail in the following description.

(2) FIG. 1 shows schematically elements of an SCR catalytic converter system, the metering valves of which can be operated by means of exemplary embodiments of the method according to the invention.

(3) FIG. 2 shows a flow diagram of an exemplary embodiment of the method according to the invention.

DETAILED DESCRIPTION

(4) A combustion engine 10, which is shown in FIG. 1, has an exhaust system 11. In the exhaust system 11 an NSC catalytic converter 21, a first SCR catalytic converter 22, which is arranged on a diesel particulate filter, and a second SCR catalytic converter 23 combined with a CUC catalytic converter (clean up catalytic converter), are arranged successively. A HWL is stored in a reducing agent tank 30, on the bottom of which a conveyor module 31 is arranged. This is transported by a feed pump in the delivery module 31 into a metering system 32, which consists of a branched pipe system. A pressure sensor 33 measures the system pressure in the metering system 32. A first metering valve 34 and a second metering valve 35 are arranged at two ends of the piping system of the metering system 32. The first metering valve 34 is located in the exhaust system 11 upstream of the first SCR catalytic converter. The second metering valve 35 is located in the exhaust system 11 upstream of the second SCR catalytic converter 23. By means of both metering valves 34, 35, HWL is metered into the exhaust system 11, from which ammonia is released there. This reacts in the SCR catalytic converters 22, 23 in a selective catalytic reaction with nitrogen oxide emissions of the combustion engine 10 to give nitrogen and water. An electronic control unit 40 controls the combustion engine 10, the conveying module 31 and the two metering valves 34, 35. It receives measurement data from the pressure sensor 33.

(5) As shown in FIG. 2, a start 50 of an exemplary embodiment of the method according to the invention is carried out when metering quantity requirements for the two metering valves 34, 35 are issued. Subsequently, a difference 51 formed between the system pressure p.sub.ist determined by means of the pressure sensor 33 or pressure model and a target pressure p.sub.soll is 6 bar in the present case, for example. Subsequently, a test 52 is carried out as to whether the deviation Δp between the system pressure p.sub.ist and the target pressure p.sub.soll obtained by this difference formation is outside a specified tolerance range. If this is not the case, no further adaptation takes place in the current system state and the HWL doses are reduced by the last calculated adaptation factors. Otherwise, a calculation 61 of a proportion r.sub.34 of the requested metering quantity of the metering valve 34 of the total metering quantity of the two metering valves 34, 35 is first calculated. For this purpose, past average values m.sub.34, m.sub.35 of the metering quantity requirements for the two metering valves 34, 35 are provided and the proportion r.sub.34 is calculated using formula 2:

(6) $\begin{array}{cc}{r}_{34}=\frac{{\stackrel{\_}{m}}_{34}}{{\stackrel{\_}{m}}_{34}+{\stackrel{\_}{m}}_{35}}& \left(\mathrm{Formula}2\right)\end{array}$

(7) By a forming a square 62 according to formula 3, a weighting factor f.sub.34 is calculated for the first metering valve 34:

(8) $\begin{array}{cc}{f}_{34}=r_{34}^2& \left(\mathrm{Formula}3\right)\end{array}$

(9) This weighting factor f.sub.34 is now, after multiplication by the current or suitably filtered pressure deviation Δp, fed to an event-based PI controller of the first metering valve 34 to perform a calculation 63 of an adaptation factor a.sub.34 of the first metering valve 34. This adaptation factor a.sub.34 is fed 64 to a valve characteristic of the first metering valve 34.

(10) The calculation of a proportion r.sub.35 of the requested metering quantity of the second metering valve 35 of a total metering quantity could in principle be carried out according to formula 4 similarly to the procedure according to formula 2:

(11) $\begin{array}{cc}{r}_{35}=\frac{{\stackrel{\_}{m}}_{35}}{{\stackrel{\_}{m}}_{34}+{\stackrel{\_}{m}}_{35}}& \left(\mathrm{Formula}4\right)\end{array}$

(12) However, since the proportion r.sub.34 of the first metering valve 34 has already been calculated, this value is used to save computing time in the electronic control unit 40 in order to calculate 71 the proportion r.sub.35 of the second metering valve 35 as the difference of the proportion r.sub.34 of the first metering valve 34 from one according to formula 5:
r.sub.35=1−r.sub.34|  (Formula 5)

(13) From this proportion r.sub.35 the weighting factor of the second metering valve 35 is calculated in a further calculation 72 according to formula 6 similarly to the procedure according to formula 3:
f.sub.35=r.sub.35.sup.2  (Formula 6)

(14) The weighting factor f.sub.35 of the second metering valve 35 is fed similarly to the procedure for the first valve to an event-based PI controller of the second metering valve 35 in order to obtain an adaptation factor a.sub.35 of the second metering valve 35. This adaptation factor a.sub.35 of the second metering valve 35 is fed to a valve characteristic of the second metering valve 35.

(15) This method is carried out continuously, i.e. as soon as the current system pressure deviation exceeds an arbitrarily applicable threshold, new values of the adaptation factors a.sub.34 and a.sub.35 are calculated. If the valve opening times are now determined from the requested metering quantities and the respective adapted valve characteristics in order to reduce the metering quantities by means of the metering valves 34, 35, the adaptation factors a.sub.34, a.sub.35 cause an adaptation of the valve opening times and thus also of the reduced metering quantities, so that the system pressure p.sub.ist can be adjusted towards the target pressure p.sub.soll again.

(16) In a further embodiment of the method, there is also the possibility, in addition to the adaptation of the valve characteristics, to adapt the stored conveying characteristic of the pump, in that by the calculation of the valve adaptation factors, an adaptation factor for the stored flow volume of the pump is additionally calculated by means of a PI controller with the pressure deviation Δp as input. This is particularly suitable in the context of a special implementation of the method in the event that when operating the system with multiple valves, the resulting valve adaptation factors all assume very similar values with a significant deviation from the nominal value (for example a.sub.34≈a.sub.35>1.15 or a.sub.34≈a.sub.35<0.85). Such behavior of the system suggests that the essential tolerance influence of the system is a deviation of the feed pump from its nominal value. In this case, the valve adaptation factors are each set to 1.0 and instead an adaptation factor for the stored flow volume of the pump is calculated by means of a PI controller with the pressure deviation Δp as input, comparable to the described method with application to the two valves, but without using a weighting factor.