METHODS FOR DETECTING A DOSING ERROR

Abstract

A method for detecting a dosing error of a reduction agent in a dosing module of an SCR catalytic converter system. The SCR catalytic converter system comprises the dosing module, which has a dosing valve and a flow valve as well as a delivery module with delivery pump. The SCR catalytic converter system, furthermore, has a return, in which a further flow valve is arranged. Said flow valve changes an effective cross-sectional area of the return. The method herein comprises the following steps: at the beginning, the dosing valve is closed (200). At a first pressure value (p.sub.1) in the system the delivery pump is switched off (201) and a measurement (202) of a first pressure rate (β.sub.RL.sup.dynamic) of the flow valve of the return subsequently takes place. Additional operation of the pump and the dosing valve occurs and a ratio of pressure rates is determined.

Claims

1. A method for detecting a dosing error of a reduction agent in a dosing module (130), which comprises a dosing valve (131) and a flow valve (132), of an SCR catalytic converter system, which comprises a delivery module (110) with a delivery pump (111) and a return (160), in which a flow valve (161), which changes an effective cross-sectional area (A.sub.eff) of the return (160) is arranged, comprising the following steps: switching off (201) the delivery pump (111) at a first pressure value (p.sub.1) in the system (100) when the dosing valve (131) is closed (200); measuring (202) a first pressure rate (β.sub.RL.sup.dynamic) of the flow valve (161) of the return (160); switching on (203) the delivery pump (111); switching off (205) the delivery pump (111) when the pressure (p) in the system (100) has again reached (204) the first pressure value (p.sub.1); opening (206) the dosing valve (131) until the pressure (p) has fallen to a second pressure value (p.sub.2); measuring (207) a second pressure rate (β.sub.RL & DV.sup.dynamic) of the flow valve (161) of the return (160) and of the dosing valve (131) when the dosing valve (131) is open; calculating (209) a ratio (V) of the two pressure rates (β.sub.RL.sup.dynamic, β.sub.RL & DV.sup.dynamic); and checking (210) the actual volumetric flow rate (Q.sub.DV) through the dosing valve (131) with the help of the ratio (V).

2. A method for detecting a dosing error of a reduction agent in a dosing module (130), which comprises a dosing valve (131) and a flow valve (132), of an SCR catalytic converter system, which comprises a delivery module (110) with a delivery pump (111) and a return (160), in which a flow valve (161), which changes an effective cross-sectional area (A.sub.eff) of the return (160) is arranged, comprising the following steps: switching off (301) the delivery pump (111) at a first pressure value (p.sub.1) in the system (100) when the dosing valve (131) is closed (300); measuring (302) a first pressure rate (β.sub.RL.sup.static) of the flow valve (161) of the return (160); switching on (303) the delivery pump (111); opening (305) the dosing valve (131) when the pressure (p) in the system (100) has again reached (204) the first pressure value (p.sub.1); switching off (306) the delivery pump (111); measuring (307) a second pressure rate (β.sub.RL & DV.sup.static) of the flow valve (161) of the return (160) and of the dosing valve (131) when the dosing valve (131) is open; calculating (309) a ratio (V) of the two pressure rates (β.sub.RL.sup.static, β.sub.RL & DV.sup.static); and checking (310) the actual volumetric flow rate (Q.sub.DV) through the dosing valve (131) with the help of the ratio (V).

3. The method according to claim 1, wherein the delivery pump (110) during both measurements (202, 207; 302, 307) is halted (201, 205; 301, 306) at the same angle of rotation (w) when the delivery pump comprises a rotating delivery pump (110), and the delivery pump (110) performs a same stroke prior to both measurements (202, 207; 302, 307) when the delivery pump comprises a linearly driven delivery pump.

4. The method according to claim 1, wherein the flow valve (161) in the return, which changes an effective cross-sectional area (A.sub.eff) of the return (160), is an orifice plate (161).

5. The method according to claim 1, wherein the flow valve (161) in the return (160), which changes an effective cross-sectional area (A.sub.eff) of the return, is a choke.

6. The method according to claim 1, wherein the pressure rate is a mean relative pressure rate (β).

7. The method according to claim 1, wherein the pressure rate is a mean absolute pressure rate.

8. The method according to claim 1, wherein the delivery pump (111) is switched off so slowly and the dosing valve (131) opened so slowly that a pressure surge of the reduction agent is avoided.

9. The method according to claim 1, wherein an additional dosing quantity during the measurement (207; 307) of the pressure rates (β.sub.RL & DV.sup.dynamic, β.sub.RL & DV.sup.static) is taken into account (211; 311) in a dosing strategy.

10. A computer program which is equipped to carry out every step of the method according to claim 1.

11. A machine-readable storage medium on which a computer program according to claim 10 is stored.

12. An electronic control unit (150), which is equipped in order to detect a dosing error of a reduction agent in an SCR catalytic converter system by means of a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description. In the figures:

[0019] FIG. 1 schematically shows a reduction agent delivery system of an SCR catalytic converter system, in which a dosing error can be detected by means of an exemplary embodiment of the method according to the invention.

[0020] FIG. 2 shows a flow diagram of an exemplary embodiment of the method according to the invention.

[0021] FIG. 3a shows a diagram of the pressure over the time according to an embodiment of the method according to the invention, wherein a dosing valve in the dynamic case is closed.

[0022] FIG. 3b shows a diagram of the pressure over the time according to an embodiment of the method according to the invention, wherein the dosing valve in the dynamic case is open after the delivery pump has been switched off.

[0023] FIG. 4a shows a diagram of the mean pressure rates with closed and open dosing valve over the time according to an embodiment of the method according to the invention for the dynamic case, in the case of which the dosing valve is not blocked.

[0024] FIG. 4b shows a diagram of the mean pressure rates with closed and open dosing valve over the time according to a further embodiment of the method according to the invention for the dynamic case, in the case of which the dosing valve is partly blocked.

[0025] FIG. 5 shows a flow diagram of a further exemplary embodiment of the method according to the invention.

[0026] FIG. 6 shows a diagram of the pressure over the time according to an embodiment of the method according to the invention, wherein a dosing valve in the static case is open prior to the delivery pump being switched off.

[0027] FIG. 7a shows a diagram of the mean pressure rates with closed and open dosing valve over the time according to an embodiment of the method according to the invention for the static case, in the case of which the dosing valve is not blocked.

[0028] FIG. 7b shows a diagram of the mean pressure rates with closed and open dosing valve over the time according to a further embodiment of the method according to the invention for the static case, in the case of which the dosing valve is partly blocked.

DETAILED DESCRIPTION

[0029] A reduction agent delivery system 100 of an SCR catalytic converter system (not displayed) is shown in FIG. 1. It comprises a delivery module 110, which comprises a rotating delivery pump 111, which is equipped to deliver reduction agent from a reduction agent tank 120 via a pressure line 121 into a dosing module 130, where the reduction agent is then sprayed into an exhaust gas system which is not shown. Additionally, the dosing module 130 comprises a dosing valve 131 which can be opened or closed and which controls the reduction agent flow to the dosing valve 130 and an orifice plate 132, which changes a volumetric flow rate Q.sub.DV of the reduction agent through the dosing module 130. Furthermore, a pressure sensor 140 is arranged in the reduction agent delivery system 100 and equipped to measure a pressure p between delivery module 110 and dosing module 130 over a period of time. An electronic control unit 150 is connected to the pressure sensor 140 and receives information regarding the pressure p in the system 100 from same. In addition, the electronic control unit 150 is connected to the delivery module, including the delivery pump 111, and to the dosing module 130, including dosing valve 131, and can control these.

[0030] In addition to this, the reduction agent delivery system 100 comprises a return 160, through which reduction agent conducted from the system back into the reduction agent tank 120. In this return 160, an orifice plate 161 is arranged which offers a local flow resistance and to that effect reduces an effective cross-sectional area A.sub.eff of the return 160 in size.

[0031] A volumetric flow rate Q.sub.RL of the reduction agent through the return 160 is regulated by the orifice plate 161 and can be calculated by way of the flow law for orifice plates, which is as follows:

[00001]$\begin{array}{cc}{Q}_{\mathrm{RL}}=A_{\mathrm{eff}}.Math.\sqrt{\frac{2}{\rho }}.Math.\sqrt{\Delta .Math..Math.p\left(t\right)}& \left(\mathrm{Formula}.Math..Math.1\right)\end{array}$

[0032] Here, A.sub.eff, as mentioned above, is the effective cross-sectional area of the orifice plate 161, p stands for a density of the reduction agent and Δp for a pressure differential upstream and downstream of the orifice plate 161. It should be noted that the volumetric flow rate Q.sub.RL depends on the root of the pressure differential Δp.

[0033] The orifice plate 132 in the dosing module 130 and the orifice plate 161 in the return 160 function identically and the orifice plate 132 in the dosing module 130 influences the flow behavior of the volumetric flow rate Q.sub.DV through the dosing valve 131 in the same manner, analogously to Formula 1, as the orifice plate 161 in the return 160 influences the volumetric flow rate Q.sub.RL through the return 160.

[0034] In a further embodiment, a choke as flow valve can be arranged in the dosing module 130 and in the return 160. In this case, the volumetric flow rate Q.sub.RL through the return 160 is calculated by way of the flow law for chokes. Here, the volumetric flow rate Q.sub.RL is proportional to the pressure differential Δp. Here, too, both chokes function in the same manner and influence the flow behavior of the volumetric flow rates Q.sub.DV and Q.sub.RL in the same manner.

[0035] For determining a dosing of the reduction agent in the dosing module 130, a volumetric flow rate Q.sub.DV of the reduction agent through the dosing valve 131 is utilized. In the following, the relationship between a volumetric flow rate Q and a change of the pressure p in the system 100 will be shown. For the calculation, we utilize a relative pressure rate β which is obtained as follows from the change in the pressure over time dp(t)/d t:

[00002]$\begin{array}{cc}\beta =\frac{1}{\sqrt{p\left(t\right)}}.Math.\frac{\mathrm{dp}\left(t\right)}{\mathrm{dt}}& \left(\mathrm{Formula}.Math..Math.2\right)\end{array}$

[0036] The change in the pressure over time dp(t)/dt can be expressed by Formula 4 via a change in volume over time dV(t)/dt and a stiffness .sub.K according to Formula 3:

[00003]$\begin{array}{cc}\kappa =V.Math.\frac{\mathrm{dp}\left(t\right)}{\mathrm{dV}\left(t\right)}& \left(\mathrm{Formula}.Math..Math.3\right)\\ \frac{\mathrm{dp}\left(t\right)}{\mathrm{dt}}=\frac{\mathrm{dp}\left(t\right)}{\mathrm{dV}\left(t\right)}.Math.\frac{\mathrm{dV}\left(t\right)}{\mathrm{dt}}=\frac{1}{V}.Math.V.Math.\frac{\mathrm{dp}\left(t\right)}{\mathrm{dV}\left(t\right)}.Math.\frac{\mathrm{dV}\left(t\right)}{\mathrm{dt}}=\frac{\kappa }{V}.Math.\frac{\mathrm{dV}\left(t\right)}{\mathrm{dt}}& \left(\mathrm{Formula}.Math..Math.4\right)\end{array}$

[0037] According to the continuity equation (Formula 5), the change in volume over time dV(t)/dt occurs throughout the volumetric flow rate Q.sub.ges. In the event that only the orifice plate 161 is open in the return 160, the total volumetric flow rate Q.sub.ges corresponds to the volumetric flow rate Q.sub.RL through the orifice plate 161.

[00004]$\begin{array}{cc}\frac{\mathrm{dV}\left(t\right)}{\mathrm{dt}}=-Q_{\mathrm{ges}}=-Q_{\mathrm{RL}}& \left(\mathrm{Formula}.Math..Math.5\right)\end{array}$

[0038] When the volumetric flow rate Q.sub.RL through the orifice plate 161 is calculated, Formula 5 and Formula 1 are inserted in Formula 3 and the result rearranged according to Formula 2. By way of this an expression for the relative pressure rate β is obtained via the characteristic quantities of the orifice plate 161:

[00005]$\begin{array}{cc}\beta =-\frac{\kappa }{V}.Math.A_{\mathrm{eff}}.Math.\sqrt{\frac{2}{\rho }}& \left(\mathrm{Formula}.Math..Math.6\right)\end{array}$

[0039] For better calculation, the relative pressure rate β is averaged from a lowest pressure p.sub.1 to a highest pressure p.sub.h according to Formula 7 in order to obtain a mean relative pressure rate β.

[00006]$\begin{array}{cc}\stackrel{\_}{\beta }=\frac{1}{p_h-p_l}.Math.{\int }_{p_l}^{p_h}.Math.\beta \left(p\right).Math.\mathrm{dp}& \left(\mathrm{Formula}.Math..Math.7\right)\end{array}$

[0040] In the application case, the integral is not analytically calculated, rather a numerical approximation is performed. Here, the integral is expressed via a corresponding Riemann sum:

[00007]$\begin{array}{cc}\stackrel{\_}{\beta }=\frac{1}{p_h-p_l}.Math.\underset{j=l}{\overset{h-1}{.Math.}}.Math.\beta \left(p_j\right).Math.\left(p_{j+1}-p_j\right)& \left(\mathrm{Formula}.Math..Math.8\right)\end{array}$

[0041] For the following exemplary embodiments, the following configuration of the reduction agent delivery system 100 is used: [0042] the delivery module 110 is designed for a maximum mass flow of the dosing module 130 of 10 kg of reduction agent per hour; [0043] the dosing module 130 is designed for a maximum mass flow of 7.2 kg of reduction agent per hour, which is injected into the exhaust gas system; [0044] the pressure line 121 is 475 cm long and has an inner diameter of 6 mm and is manually vented after pressure build-up; [0045] the method is carried out at room temperature.

[0046] FIG. 2 shows a flow diagram of an exemplary embodiment of the method according to the invention, which is described as the dynamic case in the following. At the beginning, a closing 200 of the dosing valve 131 takes place. At a fixed pressure p.sub.1, a switching-off 201 of the delivery pump 111 takes place, wherein the rotating delivery pump 111 is switched off within 200 ms and comes to a halt at a fixed angle of rotation ω. Directly following this, a measurement 202 of the mean relative pressure rate β.sub.RL.sup.dynamic of the return 160 is carried out. When the measurement 202 has been concluded, the delivery pump 111 is switched on 203 again and the pressure p in the system 100 rises. As a consequence of a query 204 it is determined when the pressure p again reaches the fixed pressure value p.sub.1. If this is the case, the delivery pump 111 is switched off 205 again. Here, too, the switching-off 205 of the delivery pump 111 takes place within 200 ms and the delivery pump 111 comes to a halt at the same angle of rotation ω. Directly following this, the dosing valve 131 is opened 206 within 200 ms and a renewed measurement 207 of the mean relative pressure rate β.sub.RL & DV.sup.dynamic of the return 160 and of the dosing valve 131 carried out. When the measurement 207 has been concluded, the dosing valve 131 is closed 208 again.

[0047] Since the return 160 and the pressure line 121, which leads to the dosing module 130, are connected, the pressure p in both lines is identical. For this reason, the two mean relative pressure rates β.sub.RL.sup.dynamic and β.sub.RL.sup.dynamic can be compared with one another. As explained previously, the relative pressure rate β, and thus also the mean relative pressure rate β, is dependent on the volumetric flow rate Q. In a further step, a calculation 209 of a ratio V between both volumetric flow rates Q.sub.RL and Q.sub.RL&DV according to Formula 9 takes place in that a quotient of the two mean relative pressure rates β.sub.RL.sup.dynamic and β.sub.RL & DV.sup.dynamic is formed.

[00008]$\begin{array}{cc}V=\frac{{\stackrel{\_}{\beta }}_{\mathrm{RL}}^{\mathrm{dynamic}}}{{\stackrel{\_}{\beta }}_{\mathrm{RL}.Math.\&.Math..Math.\mathrm{DV}}^{\mathrm{dynamic}}}=\frac{Q_{\mathrm{RL}}}{Q_{\mathrm{RL}.Math.\&.Math..Math.\mathrm{DV}}}& \left(\mathrm{Formula}.Math..Math.9\right)\end{array}$

[0048] In conclusion, a checking 210 of the actual volumetric flow rate Q.sub.DV through the dosing valve via the calculated ratio V takes place. Furthermore, the quantity which to a minor extent is additionally dosed in is taken into account 211 in a further dosing strategy.

[0049] FIGS. 3a and 3b represent the profile of the pressure p over time in the reduction agent delivery system 100 for the above described dynamic case. In FIG. 3a, the dosing valve 131 is closed and the pressure p=.sub.RL.sup.dynamic is exclusively reduced via the return 160. Once the delivery pump 111 has been switched off 201 at a pressure p.sub.1, it comes to a halt 201 at approximately 0.7 seconds. Following this, the pressure p=.sub.RL.sup.dynamic shows a reciprocal profile that is characteristic for an orifice plate.

[0050] FIG. 3b shows the profile of the pressure p=.sub.RL&DV.sup.dynamic with opened dosing valve 131. Here, the delivery pump 111 likewise comes to a halt 205 at approximately 0.7 seconds. At approximately 1.3 seconds, the dosing valve 131 is opened 206 and the pressure p=.sub.RL&DV.sup.dynamic can now be reduced both via the return 160 and also via the opened dosing valve 131. As a result of this, the reciprocal profile, compared with FIG. 3a, is changed. The measurement 207 of the mean relative pressure rate β.sub.RL&DV.sup.dynamic with open dosing valve 131 takes place over a period of time of approximately 2 seconds until the dosing valve subsequently is closed 208 again as soon as the pressure p has reached a second pressure valve p.sub.2.

[0051] In FIGS. 4a and 4b, the two mean relative pressure rates β.sub.RL.sup.dynamic and β.sub.RL & DV.sup.dynamic are respectively represented over an extended measurement duration of up to six hours, wherein the curve is constructed from the measurement points of the respective individual measurements according to the method in the dynamic case according to the invention. FIG. 4a shows a configuration in which the dosing valve 131 is not blocked. Here it is easily detectable that the mean relative pressure rate β.sub.RL & DV.sup.static of the return 160 and of the dosing valve 131 lies above the mean relative pressure rate β.sub.RL.sup.static return 160. It is noted, furthermore, that the ratio of both profiles approximately coincides. From this it can be inferred that the volumetric flow rate Q.sub.DV through the dosing valve 131 remained constant over this time and as a result the dosing did not exhibit any errors either.

[0052] FIG. 4b otherwise shows a configuration in which a third of the dosing valve 131 is blocked. Furthermore, the mean relative pressure rate β.sub.RL & DV.sup.dynamic of the return 160 and of the dosing valve 131 lies above the mean relative pressure rate β.sub.RL.sup.dynamic of the return 160. However it is noticeable that the relative interval is smaller, which points to a smaller volumetric flow rate Q.sub.DV through the dosing valve 131.

[0053] FIG. 5 represents a flow diagram of a further exemplary embodiment of the method according to the invention, which in the following is described as the static case. At the beginning, a closing 300 of the dosing valve 131 likewise takes place. Equally, at a fixed pressure p.sub.1 a switching-off 301 of the delivery pump 111 takes place, wherein the rotating delivery pump 111 is switched off within 200 ms and comes to a halt at a fixed angle of rotation ω. Directly following this, a measurement 302 of the mean relative pressure rate β.sub.RL.sup.static of the return 160 is carried out. When the measurement 302 has been concluded, the delivery pump 111 is switched on 303 again and the pressure p in the system 100 rises. As a consequence of a query 304 it is determined when the pressure p again reaches the fixed pressure value p.sub.1. In this embodiment, firstly the dosing valve 131 is now opened 305 within 200 ms and following this the delivery pump 111 switched off 306 again. Here, too, the switching-off 306 of the delivery pump 111 takes place within 200 ms and the delivery pump 111 comes to a halt at the same angle of rotation ω. The measurement 307 of the mean relative pressure rate β.sub.RL & DV.sup.static of the return 160 and of the dosing valve 131 takes place. When the measurement 307 has been concluded, the dosing valve 131 is closed 308 again.

[0054] In a further step, a calculation 309 of a ratio V of both the mean relative pressure rates β.sub.RL.sup.static and β.sub.RL & DV.sup.static is performed according to the Formula 10, in an analogous manner to that explained above.

[00009]$\begin{array}{cc}V=\frac{{\stackrel{\_}{\beta }}_{\mathrm{RL}}^{\mathrm{static}}}{{\stackrel{\_}{\beta }}_{\mathrm{RL}.Math.\&.Math..Math.\mathrm{DV}}^{\mathrm{static}}}=\frac{Q_{\mathrm{RL}}}{Q_{\mathrm{RL}.Math.\&.Math..Math.\mathrm{DV}}}& \left(\mathrm{Formula}.Math..Math.10\right)\end{array}$

[0055] In conclusion, a checking 310 of the actual volumetric flow rate Q.sub.DV through the dosing valve via the calculated ratio V also takes place here and the additionally dosed-in quantity is taken into account 311 in a further dosing strategy.

[0056] FIG. 6 shows the profile of the pressure p=.sub.RL & DV.sup.static at which the dosing valve 131 is open 305 before the switching-off 306 of the delivery pump 111. Here, the delivery pump 111 likewise comes to a halt 306 at approximately 0.7 seconds and the pressure p=.sub.RL & DV.sup.static can now be reduced both via the return 160 and also via the opened dosing valve 131.

[0057] In order to illustrate the change of the pressure profile, the mean relative pressure rates β.sub.RL.sup.static and β.sub.RL & DV.sup.static are used. In FIGS. 7a and 7b, both are shown in each case for two different configurations over an extended measurement duration of approximately 7.5 hours. In particular, the dosing valve 131 in FIG. 7a is not blocked and the analysis can be carried out in the dynamic case analogous to FIG. 4a. Here it is readily evident that the mean relative pressure rate β.sub.RL & DV.sup.static of the return 160 and of the dosing valve 131 lies above the mean relative pressure rate β.sub.RL.sup.static. It is noted, furthermore, that the ratio V of the two profiles approximately coincides and lies within the expected tolerances. From this it can be inferred that the volumetric flow rate Q.sub.DV through the dosing valve 131 remained constant over this time and as a result the dosing did not exhibit any errors either.

[0058] FIG. 7b accordingly shows a configuration in the case of which a third of the dosing valve 131 is blocked. Furthermore, the mean relative pressure rate β.sub.RL & DV.sup.static of the return 160 and of the dosing valve 131 lies above the mean relative pressure rate β.sub.RL.sup.static of the return 160. However, it is evident that the relative interval is smaller, which points to a lower volumetric flow rate Q.sub.DV through the dosing valve 131.

[0059] It should be noted that the stiffness .sub.K and thus also the mean relative pressure rates β.sub.RL.sup.dynamic, β.sub.RL & DV.sup.dynamic, β.sub.RL.sup.static and β.sub.RL & DV.sup.static greatly depend on a charging of the system 100 with air and its runtime. For this reason, these can differ for identical dosing valves 131 and a comparison of the mean relative pressure rates β.sub.RL.sup.dynamic and β.sub.RL & DV.sup.static with closed dosing valve 131, for example between FIGS. 4a, 4b, 7a and 7b, is not readily possible.