METHOD FOR DETECTING A BLOCKED PRESSURE LINE

Abstract

The invention relates to a method for detecting a blocked pressure line in an SCR system of an internal combustion engine. The SCR system comprises a feed pump, a dosing module and a pressure sensor. The method comprises the following steps: a reference signal of a pressure (p) in the pressure line is measured over a measuring time (t.sub.M) if a reducing agent solution is not dosed by the dosing module, and a signal energy of the reference signal is then calculated. A pressure signal is measured over the measuring time (t.sub.M) during the dosing of a dosing mass of the reducing agent solution by the dosing module, and a signal energy of the pressure signal is then calculated. Finally, a ratio of the signal energies of the pressure signal to the signal energy of the reference signal is calculated. The blocked pressure line is detected if the ratio falls short of a first pre-definable threshold value.

Claims

1. A method for detecting a blocked pressure line (11) in an SCR system (10) of an internal combustion engine, which has a conveyor pump (13), a metering module (15), and a pressure sensor (17), the method comprising: measuring (22) a reference signal of a pressure (p) in the pressure line (11) over a measuring time (tM) when no injection of a reducing agent solution by the metering module (15) takes place and computing a signal energy (ER) of the reference signal; measuring (32) a pressure signal over the measuring time (tM) during an injection of a metered mass of the reducing agent solution by the metering module (15) and computing a signal energy (Ep) of the pressure signal; computing (40) a ratio (VE) of the signal energy (Ep) of the pressure signal to the signal energy (ER) of the reference signal; and detecting (50) the blocked pressure line (11) if the ratio (VE) falls below a first predefinable threshold value (S1).

2. The method as claimed in claim 1, wherein the measurement (32) of the pressure signal is first carried out when the metered mass has exceeded (31) a predefined limiting mass.

3. The method as claimed in claim 1, characterized in wherein the conveyor pump (13) maintains (21) a setpoint pressure (ps) in the pressure line (11) during the measurement (22) of the reference signal.

4. The method as claimed in claim 1, wherein the conveyor pump (13) compensates for a pressure change as a result of the injection of the metered mass during the measurement (32) of the pressure signal.

5. The method as claimed in claim 1, wherein a pump speed (nR; np) of the conveyor pump (13) is detected in each case during the measurement (22) of the reference signal and during the measurement (32) of the pressure signal and the detection (50) of the blocked pressure line (11) only takes place if a ratio (Vn) of the pump speeds (nR; np) is between a predefinable second threshold value (S2) and a predefinable third threshold value (S3).

6. The method as claimed in claim 1, wherein a waiting time (tW) passes between the beginning (31) of the injection and the measuring (32) of the pressure signal.

7. (canceled).

8. A non-transitory computer-readable storage medium, containing instructions that when executed by a computer cause the computer to control an SCR system (10) of an internal combustion engine, which has a conveyor pump (13), a metering module (15), and a pressure sensor (17), to: measure (22) a reference signal of a pressure (p) in the pressure line (11) over a measuring time (tM) when no injection of a reducing agent solution by the metering module (15) takes place and computing a signal energy (ER) of the reference signal; measure (32) a pressure signal over the measuring time (tM) during an injection of a metered mass of the reducing agent solution by the metering module (15) and computing a signal energy (Ep) of the pressure signal; ompute (40) a ratio (VE) of the signal energy (Ep) of the pressure signal to the signal energy (ER) of the reference signal; and detect (50) the blocked pressure line (11) if the ratio (VE) falls below a first predefinable threshold value (S1).

9. An electronic control unit, which is configured to control an SCR system (10) of an internal combustion engine, which has a conveyor pump (13), a metering module (15), and a pressure sensor (17), to: measure (22) a reference signal of a pressure (p) in the pressure line (11) over a measuring time (tM) when no injection of a reducing agent solution by the metering module (15) takes place and computing a signal energy (ER) of the reference signal; measure (32) a pressure signal over the measuring time (tM) during an injection of a metered mass of the reducing agent solution by the metering module (15) and computing a signal energy (Ep) of the pressure signal; compute (40) a ratio (VE) of the signal energy (Ep) of the pressure signal to the signal energy (ER) of the reference signal; and detect (50) the blocked pressure line (11) if the ratio (VE) falls below a first predefinable threshold value (S1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Exemplary embodiments of the invention are illustrated in the drawings and explained in greater detail in the following description.

[0020] FIG. 1 schematically shows a reducing agent conveyor system of an SCR system, the pressure line of which can be detected by means of an exemplary embodiment of the method according to the invention.

[0021] FIG. 2 shows a flowchart of an exemplary embodiment of the method according to the invention.

[0022] FIG. 3 shows a diagram of the pressure over time for an unblocked pressure line according to an exemplary embodiment of the method according to the invention.

[0023] FIG. 4 shows a diagram of the pressure over time for a blocked pressure line according to an exemplary embodiment of the method according to the invention.

DETAILED DESCRIPTION

[0024] FIG. 1 shows an SCR system 10 for conveying reducing agent through a pressure line 11 into an SCR catalytic converter (not shown). It comprises a conveyor module 12, which comprises a pump 13, which is configured to convey reducing agent from a reducing agent tank 14. The conveyor module 12 is connected via the pressure line 11 to a metering module 15, wherein reducing agent is conveyed by the conveyor module 12 through the pressure line 11 to the metering module 15, where it is subsequently injected into an exhaust system (not shown). In addition, the SCR system 10 comprises a return conveyor line 16, which connects the conveyor module 12 to the reducing agent tank 14. Excess reducing agent is conveyed back from the conveyor module 12 into the reducing agent tank 14. Furthermore, the pressure line 11 has a pressure sensor 17, which monitors the pressure p in the pressure line 11 and is connected to an electronic control unit 18. The electronic control unit 18 is additionally connected to the conveyor module 12 and the metering module 15 and can control them. In addition, a clog 19 inside the pressure line 11 is shown in FIG. 1, which blocks the reducing agent flow between conveyor module 12 and metering module 15 and can be detected by means of an embodiment of the method according to the invention. This clog 19 can arise because the reducing agent solution freezes at low ambient temperatures. However, other factors, for example soiling, can also result in the formation of such a clog 19.

[0025] FIG. 2 shows a flowchart of an exemplary embodiment of the method according to the invention. At the beginning, there is no metering request 20 of the SCR system 10, so that no reducing agent solution is injected by the metering module 15 into the exhaust system. Thereafter, the pressure p is adjusted 21 to a setpoint pressure p.sub.s, wherein the conveyor pump 13 maintains the setpoint pressure p.sub.s. After a waiting time t.sub.W, a measurement 22 of the reference signal, that is to say of a pressure signal when no injection of a reducing agent solution is performed by the metering module 15, is performed over a measuring time t.sub.M. Subsequently, the reference signal passes through a low-pass filter 23, which suppresses long-term changes in the signal. Finally, a signal energy E.sub.R of the reference signal is computed 24 via the following formula 2. Since the measurement 22 of the reference signal was only performed over the measuring time t.sub.M, the squared reference signal is only integrated over the measuring time t.sub.M, so that the following formula 2 results from formula 1:

[00002]$\begin{array}{cc}E=\underset{t_M}{}.Math.s^2\left(t\right).Math.\mathrm{dt}& \left(\mathrm{Formula}.Math..Math.2\right)\end{array}$

[0026] During the measurement 22 of the reference signal, an averaged measurement 25 of a pump speed n.sub.R of the conveyor pump 13 is additionally performed, also over the measuring time t.sub.M.

[0027] In this exemplary embodiment, a metering request 30 is subsequently specified, in order to implement a measurement 32 of the pressure signal during an injection of a metered mass of the reducing agent solution into the exhaust system (not shown) by the metering module. In other exemplary embodiments, the measurement 32 of the pressure signal during an injection can also take place chronologically before the measurement 22 of the reference signal. Ideally, the measurement 32 of the pressure signal is carried out when a metering request is placed as a result of operating conditions of the internal combustion engine and/or due to processes running in parallel. If a beginning 31 of an injection (BIPbegin of injection period) of the metered mass is established, which injection exceeds a limiting mass m.sub.G, a waiting time tw passes until the measurement 32 of the pressure signal, during which the conveyor pump 13 compensates for a pressure change as a result of the injection of the metered mass. The measurement 32 of the pressure signal during the injection takes place over the same measuring time t.sub.M as the measurement 22 of the reference signal. The pressure signal subsequently also passes through a low-pass filter 33. As for the reference signal, the signal energy E.sub.p is thereupon computed according to formula 2. An averaged measurement 35 of the pump speed n.sub.p is also additionally performed here over the same measuring time t.sub.M.

[0028] If the signal energy ER of the reference signal and the signal energy E.sub.p of the pressure signal are available during the injection, a ratio V.sub.E is computed 40 from the two in the form of a quotient according to formula 3:

[00003]$\begin{array}{cc}{V}_E=\frac{E_p}{E_R}& \left(\mathrm{Formula}.Math..Math.3\right)\end{array}$

[0029] In a first query 41, this ratio V.sub.E of the signal energies E.sub.R and E.sub.p is compared to a first setpoint value S.sub.1, which is 1.2 in this exemplary embodiment. If the ratio V.sub.E is greater than the setpoint value S.sub.1, therefore significantly greater than 1, the method is ended 42, since there is no clog 19 or other type of blocking of the pressure line 11.

[0030] This relationship is illustrated once again in FIG. 3. In this case, there is no clog 19 or other type of blocking of the pressure line 11. A diagram of the pressure signal recorded by the pressure sensor 17 is shown in FIG. 3 for the case in which there is no metering request 20, and for the case in which the metering request 30 exists. In the range 28, the pressure p over the measuring time t.sub.M is close to the setpoint pressure p.sub.s. In contrast, with the metering request 30 existing, the pressure p in the range 38, after passage of the waiting time t.sub.W since the beginning 31 of the injection, shows a recognizably greater excitation, which is induced as a result of a change of the dynamic response due to an adaptation of the pump speed n.sub.p. As a result, the signal energy E.sub.p, while the metering request 30 exists, i.e., during injection of a metered mass of the reducing agent solution, is significantly greater than the signal energy E.sub.R when there is no metering request 20 and thus no injection. As a result, the ratio V.sub.E of the signal energies when the pressure line 11 is not blocked is significantly greater than 1.

[0031] In a further step 45 of the flowchart from FIG. 2, a ratio V.sub.n of the pump speeds n.sub.R and n.sub.p of the conveyor pump 13 is additionally computed. For this purpose, a quotient of the two pump speeds n.sub.R and n.sub.p is computed according to formula 4:

[00004]$\begin{array}{cc}{V}_p=\frac{n_p}{n_R}& \left(\mathrm{Formula}.Math..Math.4\right)\end{array}$

[0032] In a second query 46, it is then checked whether the ratio V.sub.n of the pump speeds n.sub.R and n.sub.p is within an interval formed by a second setpoint value S.sub.2 and a third setpoint value S.sub.3. In this exemplary embodiment, the second setpoint value S.sub.2 is 0.66 and the third setpoint value S.sub.3 is 1.5. It is established by this query 46 whether the two pump speeds n.sub.R and n.sub.p are nearly identical. If this is not the case, the method is ended 42, since the ratio V.sub.E of the energy signals E.sub.R and E.sub.p no longer has significance.

[0033] The blocked pressure line 11 is detected 50 when the ratio V.sub.n of the pump speeds n.sub.R and n.sub.p in the case of the second query 46 is between the second setpoint value S.sub.2 and the third setpoint value S.sub.3 and in addition the first query shows that the ratio V.sub.E of the energy signals E.sub.R and E.sub.p is less than or equal to the first setpoint value S.sub.1.

[0034] The case of the pressure line 11 blocked by the clog 19 is shown in FIG. 4. A diagram is also shown of the pressure signal recorded by the pressure sensor 17 for the case in which there is no metering request 20, and for the case in which the metering request 30 exists. Similarly to FIG. 3, the pressure p in the range 29 for the measuring time tM is close to the setpoint pressure p.sub.s. In the measurement 22 of the reference signal, no differences are expected here between a blocked and an unblocked pressure line 11 if the other operating conditions are unchanged. In the range 39, meanwhile, differences are apparent from the range 38 from FIG. 3. The profile of the pressure p when the metering request 30 exists approximately corresponds to the profile of the pressure p when there is no metering request 20 even after passage of the waiting time t.sub.W since the beginning 31 of the injection. This relationship is proven, since the pressure p behaves in the same way with blocked pressure line 11 as with closed metering module 15. Therefore, a blocked pressure line 11 can be detected 50 if the signal energies E.sub.R and E.sub.p approximately correspond or the signal energy E.sub.R of the reference signal is even greater than the signal energy E.sub.p of the pressure signal during injection and accordingly the ratio V.sub.E is less than or equal to the first setpoint value S.sub.1. In this exemplary embodiment, a clog 19 was used as a cause of the blocked pressure line 11. However, other factors, for example a blocked metering module 15, can also be responsible for this.