Method for controlling a reflux valve and exhaust system

Abstract

A method for controlling a return valve of an exhaust system and to an exhaust system with a control unit which is configured to carry out the method. The method is based on the object of avoiding an overpressure in the line system for urea solution as a result of a reduction in the injection rate. The method includes the steps of determining whether one or more of the following states are present during the operation of the exhaust system: a) an injection rate per unit of time of urea solution of the dosing valve is less than or equal to a predefined injection limit, b) a pressure measured by the pressure sensor in the line system overshoots a predefined first upper pressure limit (P2). The return valve is opened for a first predefined opening duration (Δt1) if states a) and b) are present and at least one of the states has already been present for at least a predefined period of time (Δta). The return valve is closed after the first predefined opening duration (Δt1) has elapsed.

Claims

1. A method for controlling a return valve of an exhaust system, comprising the steps of: providing a catalytic converter system; providing a urea solution tank; providing at least one dosing valve for injecting urea solution into the catalytic converter system; providing a line system which enables urea solution to flow from the urea solution tank to the dosing valve and back; providing a pump arranged between the urea solution tank and the dosing valve in the line system; providing a return valve arranged between the dosing valve and the urea solution tank in the line system; and providing a pressure sensor which is configured to measure the pressure in the line system; determining whether one or more of the following states are present during the operation of the exhaust system: a) an injection rate per unit of time of urea solution of the dosing valve is less than or equal to a predefined injection limit, b) a pressure measured by the pressure sensor in the line system overshoots a predefined first upper pressure limit, opening the return valve for at least one predefined opening duration (Δt1) if states a) and b) are present and at least one of the states has already been present for at least a predefined period of time (Δta); closing the return valve after the at least one predefined opening duration (Δt1) has elapsed; after the return valve is closed, opening the return valve at least one additional time for a second predefined opening duration (Δt2), where the second predefined opening duration (Δt2) is less than the at least one predefined opening duration (Δt1); closing the return valve after the return valve has been opened the at least one additional time.

2. The method of claim 1, further comprising the steps of prior to opening the return valve the at least one additional time, maintaining the return valve closed for a closing duration (ts1, ts2, ts3) of at least 250 ms.

3. The method of claim 1, further comprising the steps of: after the return valve is closed, determining whether a predefined lower pressure limit has been undershot; reopening the return valve for a further predefined opening duration (Δt2, Δt3, Δt4) if the lower pressure limit has not been undershot.

4. The method of claim 1, further comprising the steps of adapting the at least one predefined opening duration (Δt1, Δt2, Δt3, Δt4) if it is determined that, after at least one predefined opening duration (Δt1, Δt2, Δt3, Δt4) has elapsed, the measured pressure lies outside a tolerance around an expected pressure.

5. The method of claim 1, further comprising the steps of providing the predefined period of time (Δta) to be more than 5 seconds.

6. The method of claim 1, further comprising the steps of providing the predefined period of time (Δta) to be between 5 and 60 seconds.

7. The method of claim 1, further comprising the steps of providing the predefined first upper pressure limit (P2) to be 120% of an operating pressure for the injection of the urea solution.

8. The method of claim 1, further comprising the steps of providing that the predefined first upper pressure limit (P2) to be at least 1 bar above an operating pressure (P1).

9. An exhaust system comprising: a catalytic converter system; a urea solution tank; at least one dosing valve for injecting urea solution into the catalytic converter system; a line system which enables urea solution to flow from the urea solution tank to the dosing valve and back; a pump arranged between the urea solution tank and the dosing valve in the line system; a return valve arranged between the dosing valve and the urea solution tank in the line system; a pressure sensor which is configured to measure the pressure in the line system; and a control unit which is connected in a communicating manner to the dosing valve, the pump, the return valve and the pressure sensor; wherein the control unit determines whether at least one of the following states are present during the operation of the exhaust system: a) an injection rate per unit of time of urea solution of the dosing valve is less than or equal to a predefined injection limit, b) a pressure measured by the pressure sensor in the line system overshoots a predefined first upper pressure limit (P2); wherein the return valve is opened for at least one predefined opening duration (Δt1) if states a) and b) are present and at least one of the states has already been present for at least a predefined period of time (Δta); wherein after the return valve is closed, the return valve is opened at least one additional time for a second predefined opening duration (Δt2), and the second predefined opening duration (Δt2) is less than the at least one predefined opening duration (Δt1); wherein the return valve is closed after the return valve has been opened the at least one additional time.

10. The exhaust system of claim 9, wherein the return valve is closed after the at least one predefined opening duration (Δt1) has elapsed.

11. The exhaust system of claim 9, the line system further comprising lines composed of polyamide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-described characteristics, features of this invention and the manner in which they are achieved will become clearer and more distinctly comprehensible in conjunction with the following description of the exemplary embodiments, which will be discussed in more detail in conjunction with the drawings, in which:

(2) FIG. 1 shows a sketch of an embodiment of an exhaust system according to the invention;

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

(4) FIG. 3 is a schematic illustration of the pressure profile in the line system in an embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

(6) FIG. 1 shows a sketch of an embodiment of an exhaust system 1 according to the invention. The exhaust system 1 includes a catalytic converter system 2, which in this case includes for example a diesel oxidation catalytic converter 3 and an SCR catalytic converter 4. The catalytic converter system 2 may however also include further components and/or other catalytic converter components.

(7) The exhaust system 1 also includes a urea solution tank 5 for accommodating a supply of aqueous urea solution such as AUS32/Adblue©. A dosing valve 6 is provided for injecting urea solution into the catalytic converter system 2. The exhaust system 1 includes a line system 7 which enables urea solution to flow from the urea solution tank 5 to the dosing valve 6 and back. A pump 8 is arranged in the line system 7 between the urea solution tank 5 and the dosing valve 6 in order to supply urea solution at operating pressure (for example 5 bar) to the dosing valve 6.

(8) A return valve 9 is arranged in the line system 7 between the dosing valve 6 and the urea solution tank 5. The return valve 9 is in this case a normally open solenoid valve.

(9) The line system 7 is illustrated here only in one possible layout. The individual lines of the line system 7 may also run differently. For example, a feed line from the pump 8 to the dosing valve 6 may be separate from a return line from the dosing valve 6 to the return valve 9, and the urea solution flow occurs only through a prechamber of the dosing valve 6.

(10) The exhaust system furthermore includes a pressure sensor 10 which is configured to measure the pressure in the line system 7. Furthermore, a control unit 11 is provided which is connected in a communicating manner to the dosing valve 6, the pump 8, the return valve 9 and the pressure sensor 10.

(11) The control unit 11 is configured to carry out a method according to the invention. For this purpose, it may be equipped with appropriate control software. The control software may include machine learning algorithms. For example, a predefined opening duration may be adapted by a machine learning algorithm if it is determined that, after the predefined opening duration has elapsed, the measured pressure lies outside a tolerance around an expected pressure. In this way, it is ensured that any incorrect calibrations in the method or changes in the opening behavior of the return valve 9 are compensated for. The return valve 9 may for example be a solenoid valve with a diaphragm, in which the diaphragm may slowly become worn, or the magnet force may change (for example owing to residual magnetism), over the course of time. An adaptive adaptation of the predefined method parameters is therefore desirable.

(12) The line system 7 may include lines made of relatively inexpensive polyamide, and does not necessarily require robust, elastic and pressure-resistant lines (such as, for example, lines made of ethylene propylene diene monomer). With the method according to the invention, pressure peaks above the operating pressure which last for long periods of time may be avoided, and thus the demands on the line material are reduced.

(13) The exhaust system 1 also includes an exhaust-gas sensor 12, which measures the composition of the exhaust gases downstream of the SCR catalytic converter 4 in the exhaust-gas flow and determines the amount of nitrogen oxides. The injection rate of urea solution may thus be adapted to the exhaust-gas emissions in order to keep these as low as possible. The exhaust system 1 furthermore includes a temperature sensor 13 which measures the temperature of the exhaust gases, which may likewise be incorporated in the determination of the required injection rate of urea solution. The temperature sensor 13 may also be arranged at a different point in the catalytic converter system 2, and is in this case arranged downstream of the SCR catalytic converter 4 in the exhaust-gas flow merely by way of example.

(14) FIG. 2 discloses a flow diagram of an embodiment of the method according to the invention. According to the invention, for the control of the exhaust system 1 described above, a method is provided which includes the following steps:

(15) After the start, determining in step 100 whether one or more of the following states are present during the operation of the exhaust system 1:

(16) a) an injection rate per unit of time of urea solution of the dosing valve 6 is less than or equal to a predefined injection limit,

(17) b) a pressure measured by the pressure sensor 10 in the line system 7 overshoots a predefined first upper pressure limit.

(18) In step 110, the return valve 9 is opened for a first predefined opening duration if states a) and b) are present and at least one of the states has already been present for at least a predefined period of time. Otherwise, the return valve 9 remains closed and the method returns to the start. This may be referred to as pressure-based closed-loop control.

(19) Following step 110, the return valve 9 is closed again in step 120 after the first predefined opening duration has elapsed.

(20) In step 130, it is decided whether the return valve 9 will be reopened in the current opening sequence. This may be performed for example by virtue of the pressure sensor 10 determining whether the pressure overshoots a second upper pressure limit within a minimum closing duration (for example 250 ms) (for example a second upper pressure limit of 5.2 bar in the case of a first upper pressure limit of 6 bar). A series of descending upper pressure limits may be predefined for an opening sequence, whereby the overpressure is returned to the operating pressure gradually and in a controlled manner. A single opening step makes it much more difficult to attain the operating pressure as accurately as possible.

(21) Alternatively, the decision as to whether the return valve 9 will be opened a further time may be made by whether the pressure has undershot the operating pressure or a tolerance limit above the operating pressure has been undershot.

(22) The first predefined opening duration and any second, third, fourth etc. predefined opening durations may be predefined as a sequence. The lengths of the opening durations of an opening sequence may be in a descending order, for example 10 ms, 8 ms, 6 ms, 4 ms.

(23) Individual predefined opening durations or entire sequences of opening durations may, in the decision with regard to a first opening of the return valve 9, be dependent on the start pressure. Depending on the temperature of the exhaust system, the pressure in the line system 7 may increase at different rates after a reduction in the injection rate and thus require pressure dissipation with different intensity. For example, in the presence of a relatively high overpressure at the beginning of the sequence, only the first opening duration may be relatively long, or all of the opening durations of the sequence may be relatively long (and vice versa in the case of a relatively low overpressure above the upper pressure limit). The tendency is for the major part of the overpressure to be dissipated in the first opening duration, which is why it may be sufficient for only the first opening duration to be made pressure-dependent.

(24) Subsequently, in step 140, the return valve 9 is closed again in step 150 after the second predefined opening duration has elapsed. For the sake of clarity, the method ends here after two possible openings of the return valve 9 and starts again. The method may however include three, four, five or more openings of the return valve 9 in a sequence, wherein the number of opening processes actually carried out in a sequence, as described above, may be dependent on the pressure reached after each opening in the sequence.

(25) FIG. 3 shows a schematic illustration of the pressure profile in the line system 7 in an embodiment of the method according to the invention. Here, P1 denotes the operating pressure and P2 denotes the first upper pressure limit. As described in the introduction, in the event of a transition from a high injection rate to a low injection rate of urea solution, a pressure increase in the already pressurized urea solution in the line system 7 occurs owing to external heat from the exhaust system 1 (more specifically owing to the hot exhaust gases in the catalytic converter system 2). As a result, the pressure in the line system 7 increases until it overshoots the first upper pressure limit P2 at the time t0. If the pressure then remains above the first upper pressure limit for longer than the predefined period of time Δta (for example in the range of 5-60 seconds, depending on the embodiment of the exhaust system), and at the same time the injection rate remains below the injection limit, the return valve 9 is, according to the method, opened for a first opening duration Δt1 (for example 10 ms) when the period of time Δta elapses. When the first opening duration Δt1 elapses, the return valve 9 is closed again.

(26) The pressure dissipation occurs here sequentially, wherein the number of opening processes and the opening durations may be predefined in a sequence. In this exemplary embodiment, the sequence includes four opening processes.

(27) The return valve 9 remains closed between every two opening processes for a first, second and third closing duration ts1, ts2, ts3 (for example in each case at least 250 ms). In this way, it may for example be ensured that an exact pressure measurement is present before a decision is made as to whether the return valve will be reopened. At the same time, it is determined whether the pressure is increasing again.

(28) In one embodiment, after each closure of the return valve 9, it is determined whether a predefined lower pressure limit (for example P1 or P1+ΔP, where ΔP<0.1 bar) has been undershot. If the lower pressure limit has not been undershot, the return valve 9 is reopened for a further predefined opening duration Δt2, Δt3, Δt4. The return valve 9 may for example be reopened if the pressure still lies above the operating pressure P1. It is also possible for the respective reopening of the return valve 9 to be linked to an overshooting of a predefined second upper pressure limit, third upper pressure limit, fourth upper pressure limit etc. in each case after the previous closure of the return valve 9. If these further upper pressure limits are overshot for example within the closing duration ts1, ts2, ts3 between opening processes, then the return valve is reopened; if not, then the method is ended and the valve is reopened only in the case of the cumulative presence, according to the invention, of states a)+b) and the enduring presence of at least one of the states.

(29) It is also possible for at least one predefined opening duration Δt1, Δt2, Δt3, Δt4 to be adapted if it is determined that, after the predefined opening duration Δt1, Δt2, Δt3, Δt4 has elapsed, the measured pressure lies outside a tolerance around an expected pressure. In this way, it is ensured that any incorrect calibrations in the method or changes in the opening behavior of the return valve 9 are compensated for.

(30) The predefined opening durations Δt1, Δt2, Δt3, Δt4 may for example be dependent on an opening start pressure P3 in the line system when the period of time Δta elapses. The predefined opening durations Δt1, Δt2, Δt3, Δt4 etc. may be present in the form of a table or function which is dependent on the opening start pressure P3 and be correspondingly selected when the period of time Δta elapses.

(31) Further upper pressure limits are not shown here for the sake of clarity, though these may be part of the method in order to determine whether or not further (second, third, fourth, etc.) openings of the return valve should be performed in the sequence of the method.

(32) Although the invention has been illustrated and described in more detail by way of preferred exemplary embodiments, the invention is not restricted by the disclosed examples and other variations may be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention.

(33) The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.