Improved pressure regulation in systems for exhaust gas aftertreatment

Abstract

The invention relates to a method for regulating the pressure in a pressurized supply line for feeding a reactant for selective catalytic reduction into an exhaust gas flow in an exhaust gas aftertreatment system, the exhaust gas aftertreatment system having: a feed pump for feeding the reactant; the supply line is fluidically connected to the delivery pump, a pressure regulator, which is designed to set the delivery power of the delivery pump as a function of the pressure of the reactant in the supply line by means of a regulation scheme having at least an integral component, the method comprises the following steps: detecting the pressure of the reactant in the supply line, detecting whether a pressure profile of the pressure of the reactant in the supply line, which is characteristic for the presence of air bubbles in the reactant, has occurred, -performing a reset of the integral component as a function of detecting a pressure profile characterizing the occurrence of air bubbles.

Description

Technical Field

[0001] The invention relates to a method for regulating the pressure in a supply line under pressure for the input of a reactant for selective catalytic reduction. The invention further relates to a pressure regulator for regulating the pressure in a supply line under pressure for the input of a reactant. The invention further relates to an exhaust gas aftertreatment system for aftertreatment of exhaust gases in an exhaust gas flow by means of selective catalytic reduction. The invention further relates to an exhaust gas equipment of a motor vehicle comprising an exhaust gas aftertreatment system, and a motor vehicle comprising an exhaust gas equipment having an exhaust gas aftertreatment system. Background Art

[0002] In systems for exhaust gas aftertreatment, the proportion of nitrogen oxides contained in the exhaust gas flow is reduced by means of selective catalytic reduction (SCR). In such exhaust gas aftertreatment systems, for example, a delivery device can be provided which supplies the exhaust gas flow with the reactants required for the catalytic conversion. It has been found that in the currently used control concepts for the pressure of the reactants, pressure peaks occur, which are caused by the intake of air.

[0003] It is therefore an object of the present invention to provide an improved control of the pressure at which the reactants are present, in which pressure peaks of this type are avoided. Summary of the invention

[0004] The invention relates to a method for regulating the pressure in a pressurized supply line for supplying a reactant for selective catalytic reduction to an exhaust gas flow in an exhaust gas aftertreatment system, wherein the exhaust gas aftertreatment system has:

[0005] - a delivery pump for delivering the reactants,

[0006] a supply line for supplying a reactant to the exhaust gas stream, wherein the supply line is fluidically connected to a delivery pump,

[0007] a pressure regulator which is designed to set the delivery capacity of the delivery pump as a function of the pressure of the reactant in the supply line by means of a control strategy which has at least an integral component,

[0008] The method comprises the following steps:

[0009] - detect the pressure of the reagent in the supply line,

[0010] - detecting whether a pressure curve of the pressure of the reactant in the supply line occurs which is characteristic of the presence of air bubbles in the reactant,

[0011] - Resetting the integral component is carried out as a function of the detection of a pressure curve which is characteristic of the occurrence of air bubbles.

[0012] In the solutions of the prior art, the pressure rise that can be observed when air bubbles appear can be caused in particular by the integral component of the control scheme. The solution according to an embodiment of the invention therefore proposes to detect the pressure trend of the pressure of the reactant that is characteristic for the appearance of air bubbles and to reset the integral component of the control scheme when such a characteristic pressure trend appears. In this way, it can be achieved, for example, that the pressure regulator can react to the pressure rise caused by the appearance of air bubbles faster than in previous solutions. In particular, it can be achieved, for example, that the pressure is adjusted back to the target value by the pressure regulator within a shorter time.

[0013] It is thus possible, in particular, to avoid reagent pressure peaks of the reagent in the supply line. In particular, it is thus possible, for example, to avoid a complete or partial shutdown of the exhaust gas aftertreatment system due to pressure peaks. The reagent can be, for example, a reaction solution. By avoiding pressure peaks, it is possible, for example, to reduce the hydraulic load of the components of the exhaust gas aftertreatment system. This can, for example, extend the life of the components of the exhaust gas aftertreatment system, in particular the life of the conveying device and the dosing device. In addition, for example, an improved dosing accuracy can be obtained.

[0014] The invention further relates to a pressure regulator for regulating the pressure in a pressurized supply line for supplying a reactant for selective catalytic reduction into an exhaust gas flow in an exhaust gas aftertreatment system, wherein the exhaust gas aftertreatment system comprises a delivery pump for conveying the reactant, which delivery pump is fluidically connected to the supply line, wherein the pressure regulator is designed to:

[0015] - regulating the delivery capacity of the delivery pump as a function of the pressure of the reactant in the supply line by means of a control strategy which has at least an integral component,

[0016] - detecting a pressure curve of the pressure of the reactant in the supply line which is characteristic of the presence of air bubbles in the reactant, and

[0017] - Resetting the integral component is carried out as a function of the detection of a pressure curve which is characteristic of the occurrence of air bubbles.

[0018] The invention further relates to an exhaust gas aftertreatment system for exhaust gas aftertreatment in an exhaust gas flow by means of selective catalytic reduction, wherein the exhaust gas aftertreatment system comprises:

[0019] - a delivery pump for delivering the reactants,

[0020] a supply line for supplying a reactant to the exhaust gas stream, wherein the supply line is fluidically connected to a delivery pump,

[0021] a pressure regulator which is designed to regulate the delivery capacity of the delivery pump as a function of the pressure of the reactant in the supply line by means of a regulation strategy which has at least an integral component,

[0022] Among others, the pressure regulator is designed for:

[0023] - detecting a pressure curve of the pressure of the reactant in the supply line which is characteristic of the presence of air bubbles in the reactant, and

[0024] - Resetting the integral component is carried out as a function of the detection of a pressure curve which is characteristic of the occurrence of air bubbles.

[0025] The invention furthermore relates to an exhaust system for a motor vehicle, comprising an exhaust gas aftertreatment system as described above.

[0026] The invention furthermore relates to a motor vehicle comprising an exhaust gas installation as described above with an exhaust gas aftertreatment system.

[0027] According to a preferred specific embodiment, the control strategy has a proportional component and an integral component.

[0028] The pressure regulator is preferably designed to regulate the pressure of the reactant in the supply line to a target pressure value.

[0029] Advantageously, the pressure regulator is designed to regulate the rotational speed of the delivery pump as a function of the pressure of the reactant in the supply line.

[0030] According to a preferred embodiment, the detection of a pressure trend that is characteristic of the occurrence of air bubbles includes detecting whether a lower threshold value of the pressure is fallen below, in particular for a predetermined period of time. When air bubbles enter the exhaust gas aftertreatment system, a pressure drop can first occur, for example. This pressure drop can be detected, for example, by means of a lower threshold value.

[0031] According to a further preferred embodiment, the detection of a pressure profile that is characteristic of the occurrence of air bubbles includes detecting whether a lower pressure threshold is initially undershot for a predetermined period of time and an upper pressure threshold is subsequently exceeded. For the occurrence of air bubbles in an exhaust gas aftertreatment system, it is typical that after an initial pressure drop, a subsequent pressure increase occurs. This pressure increase can be detected, for example, using an upper pressure threshold.

[0032] It is advantageous to limit the number of resets of the integral component that are performed successively. In this way, for example, an endless cycle of resets can be avoided.

[0033] The number of performed resets of the integral component is preferably counted by means of a counter, wherein, if the number of performed resets exceeds a predefined maximum value, no further reset of the integral component is performed at least for a predefined second time period.

[0034] According to a preferred specific embodiment, if the number of performed resets exceeds a predefined maximum value, a time interval is started, wherein after the time interval has elapsed a counter is reset for the number of performed resets.

[0035] Preferably the exhaust aftertreatment system comprises a tank for the reactant. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The embodiments are explained in more detail below with reference to the accompanying drawings.

[0037] Figure 1 An exhaust aftertreatment system is shown;

[0038] Figure 2 shows a detailed diagram of an exhaust aftertreatment system;

[0039] Figure 3 shows the pressure of the reactants and the rotation speed of the delivery pump unit as a function of time in a prior art solution;

[0040] Figure 4 A flow chart showing a method for pressure regulation;

[0041] Figure 5 Shown in use Figure 4 In the case of the method shown the pressure of the reactants and the rotational speed of the delivery pump unit as a function of time. DETAILED DESCRIPTION

[0042] Figure 1 An exhaust gas aftertreatment system, in particular for a diesel engine, is shown, which is designed in particular to reduce the proportion of nitrogen oxides in the exhaust gas of the engine by means of selective catalytic reduction (SCR). To carry out the selective catalytic reduction, a reactant, in particular a reaction solution, such as an aqueous urea solution, known under the symbol "AdBlue", is added to the exhaust gas flow.

[0043] exist Figure 1The exhaust gas aftertreatment system shown in FIG. 1 comprises an exhaust gas line 2 and a catalyst 4, wherein an exhaust gas flow 6 flows through the exhaust gas line 2 and the catalyst 4. The catalyst 4 is designed to catalyze the conversion of nitrogen oxides contained in the exhaust gas flow 6 with supplied reactants, wherein nitrogen and water are obtained as a result of the conversion. In this case, the temperature and the nitrogen oxide content of the exhaust gas are monitored by means of a first temperature sensor 8, a second temperature sensor 10 and a NOx sensor 12.

[0044] In order to supply the reactant to the exhaust gas flow 6, a dosing unit 14 is provided at the exhaust gas line 2. The dosing unit 14 can be designed, for example, to spray the reactant into the exhaust gas flow 6. The delivery device 16 is fluidically connected to the dosing unit 14 via a supply line 18. The delivery device 16 is designed to deliver the reactant to the dosing unit 14 via the supply line 18. Here, the delivery capacity is adjusted so that the pressure in the supply line 18 is adjusted to a predetermined target value, for example to 9 bar. The delivery device 16 is fluidically connected to a tank 24 via a suction line 20 and a return line 22, which contains a volume 26 of the reactant.

[0045] The reactant contained in the tank 24 is supplied to the delivery device 16 via the suction line 20 and is delivered to the dosing unit 14 by the delivery device 16. Excess reactant returns to the tank 24 via the return line 22. A third temperature sensor 28 is arranged in the wall of the tank 24, which is designed to measure the temperature of the reactant. In addition, a filling state sensor 30 is installed at or in the tank 24.

[0046] In order to preheat the volume 26 of the reactant contained in the tank 24, the coolant heated by the motor is conducted through the first coolant line 32, the heating element 34 and the second coolant line 36. The coolant is then conducted through the delivery device 16 via the second coolant line 36 and discharged via the third coolant line 38 in order to heat the reactant within the delivery device 16.

[0047] The metering unit 14 , which is heated greatly by the exhaust gas flow 6 flowing past, is cooled by means of the motor coolant. To cool the metering unit 14 , the motor coolant is passed through a coolant supply line 40 , the metering unit 14 and a coolant return line 42 .

[0048] For controlling the dosing unit 14, a dosing control unit 44 may optionally be provided. The dosing control unit 44 is designed to transmit a control signal 46 to at least one actuator, in particular to the dosing unit 14. Furthermore, the dosing control unit 44 is designed to receive and evaluate a sensor signal 48 of at least one sensor, for example a filling level sensor 30. The dosing control unit 44 may also be connected to a motor CAN bus 50 and / or to a diagnostic CAN bus 52.

[0049] exist Figure 2 Again, this is shown in detail Figure 1 The function of the exhaust gas aftertreatment system is shown in Figure . Figure 2 1 shows a delivery device 16, which includes a delivery pump unit 54 with a pump 56, which is driven by a pump motor 58. The delivery pump unit 54 can be optionally equipped with an inlet valve 60 and an outlet valve 62. During operation, the delivery pump unit 54 draws the reactant stored in the tank 24 through the suction line 20. The drawn reactant is conveyed through the reversing valve 64, the delivery pump unit 54 and is conveyed again through the reversing valve 64 and through the pressure buffer 66 and the supply line 18 to the dosing unit 14. The dosing unit 14 includes a dosing valve 68.

[0050] A regulating unit 70 is provided for controlling the processes in the exhaust gas aftertreatment system. The regulating unit 70 essentially comprises a metering valve control 72 for controlling the metering valve 68. The metering valve control 72 can be designed, for example, as Figure 1 A portion of a dosing control unit 44 is shown in FIG.

[0051] A pressure sensor 74 is provided in the delivery device 16, which is designed to detect the pressure of the reactant in the supply line 18. The pressure sensor signal generated by the pressure sensor 74 is supplied to the control unit 70 and evaluated there by a pressure signal evaluation 76. The pressure signal evaluation 76 is designed to determine the actual value of the pressure in the supply line 18 based on the pressure sensor signal.

[0052] The regulating unit 70 further comprises a pressure regulator 78, which is designed to regulate the delivery capacity of the delivery pump unit 54 as a function of a predetermined target value for the pressure and an actual value of the pressure provided by the pressure signal evaluation unit 76, so that the pressure in the supply line 18 approaches the target value. The pressure regulator 78 is designed to generate a suitable control signal for the delivery pump unit 54 and transmit it to the delivery pump unit. For example, the rotational speed of the delivery pump unit 54 can be adapted as a function of the control signal.

[0053] The supply line 18 is fluidically connected to a return line 80. By means of the return line 80, a return throttle valve 82 and an optionally provided shut-off valve 84, the reactant can be conducted from the supply line 18 back to the tank 24, if necessary.

[0054] The regulating unit 70 further comprises a directional valve control 86 for the directional valve 64. Figure 2 In the position shown in FIG. 1 , the reactant is conveyed from the tank 24 to the supply line 18 . By actuating the reversal valve 64 , the conveying direction can be reversed in order to convey the reactant from the supply line 18 back to the tank 24 , for example.

[0055] Furthermore, the control unit 70 comprises a heating control system 88 for the conveyor device 16 , wherein the heating control system 88 is designed to keep the conveyor device 16 at a predefined temperature.

[0056] The pressure regulator 78 will be discussed in more detail below. As already described above, the pressure regulator 78 is designed to regulate the pumping capacity of the delivery pump unit 54 as a function of a target value for the pressure and an actual value for the pressure so that the pressure in the supply line 18 approaches the target value. In this case, a proportional-integral regulator is preferably used to regulate the pumping capacity, whose regulation scheme has a proportional component and an integral component. Such a regulator is also referred to as a PI regulator.

[0057] In the PI regulators currently used, it is already provided that a reset of the integral component is performed in certain situations, that is, the integral component of the PI regulator is reset to zero in certain situations. In the PI regulators currently used in the prior art, it is provided on the one hand that the integral component is reset when the supply of the reagent is started, for example when the vehicle is started. On the other hand, it is provided that the integral component is reset when a system check for detecting a blockage of the hydraulic pressure is performed.

[0058] During operation, it is possible for air to escape from the tank 24 through the suction line 20 into the delivery device 16. In this case, the performance of the delivery pump unit 54 is significantly adversely affected by the air.

[0059] Due to the ingress of air, the pressure in the supply line 18 initially drops. As a result, a higher rotational speed of the delivery pump unit 54 (up to a maximum limit) is set by the integral component of the PI controller in order to bring the pressure back to the target value. However, as soon as air escapes from the delivery device 16, a rapid increase in pressure to values ​​above the target value of, for example, 9 bar occurs, since due to the integral component of the control concept the control cannot react quickly enough to the pressure increase and the rotational speed of the delivery pump unit 54 cannot be reduced quickly enough.

[0060] Typically, the occurrence of air bubbles in the conveying device 16 initially leads to a drop in pressure in the supply line 18 , wherein this pressure drop is then followed by a sudden, sharp increase in pressure due to the properties of the PI controller.

[0061] exist Figure 3 Such a sudden pressure rise, which can be observed in pressure regulators of the prior art, is shown in FIG. The pressure curve 90 shows the pressure of the reactant in the supply line 18 as a function of time, whereas the curve 92 shows the rotational speed of the delivery pump unit 54 as a function of time. After the air bubbles have left the delivery device 16 again, a pressure rise occurs, as indicated by the arrow 94. In this case, the pressure increases to values ​​that are clearly above the nominal pressure of 9 bar. As soon as the nominal pressure of 9 bar is exceeded, the rotational speed of the delivery pump unit 54 is reduced, as shown in FIG. Figure 3 As shown by arrow 96 in FIG. 1 . However, due to the integral component of the control scheme, the speed is only slowly reduced. It can be seen in the pressure curve 90 that the pressure increase is gradually adjusted during the phase 98. The pressure then slowly drops back to the nominal pressure in the range marked by arrow 100. However, stable pressure conditions have not yet been achieved in the range marked by arrow 100 either.

[0062] exist Figure 3 The pressure rise shown in gives rise to a number of problems: Due to the rapid pressure rise, the pressure in the hydraulic system is too high. In general, pressure peaks lead to a higher load on the entire hydraulic system. If the pressure reaches a pressure above the threshold value of 12.5 bar determined for the components for a period of more than 5 seconds, there is even a risk of shutting down the system. In addition, the service life of the components, in particular the life of the conveying device 16 and the dosing unit 14, is sometimes reduced due to pressure peaks. Dosing accuracy can also be adversely affected by the excessively high pressure, which can lead to higher dosing quantities, for example. These disadvantages can lead to customer complaints.

[0063] In order to avoid these disadvantages, the solution according to one embodiment of the invention provides for detecting the presence of air bubbles in the supply line and, when air is detected, causing a reset of the integral component of the pressure regulator. By resetting the integral component to zero, the sharp pressure rise that can be observed in previous solutions of the prior art, which is caused in particular by the integral component of the control concept (commonly), can be avoided or reduced. As a result, the pressure in the supply line can be adjusted back to the target value in a relatively short time.

[0064] Preferably, it is provided that the pressure is monitored in order to detect the occurrence of air bubbles in the supply line 18 and to detect whether a pressure curve characteristic of the occurrence of air bubbles occurs. When air enters the supply line 18 via the suction line 20 and the delivery pump unit 54, this initially causes a pressure drop. The pressure control responds to this pressure drop by increasing the delivery capacity of the delivery pump unit 54, which thus causes the pressure in the supply line 18 to increase.

[0065] This characteristic pressure trend can preferably be detected by means of two threshold values, a lower threshold value and an upper threshold value, wherein, when air appears in the system, the lower threshold value is firstly lowered and then the upper threshold value is exceeded. In order to reliably identify an event, it is preferably to be lower than the lower threshold value for at least a first predetermined duration t1, wherein the first duration t1 can be detected by means of a timer provided for this purpose. The first duration t1 can be determined, for example, as 1 second. In this way, the identification of an event is made insensitive to pressure fluctuations of shorter duration, which can be caused, for example, by a rigid system during a long operating time of more than four hours or due to high dosing requirements. The situation of exceeding the upper threshold value is then used as a trigger for resetting the integral component of the control scheme, in order to thus avoid a further sharp rise in pressure.

[0066] exist Figure 4 Flow chart of shows a method for pressure regulation. The method is started in step 102. In query step 104, it is queried whether the current pressure of the reactant in the supply line 18 is below the lower threshold and therefore also below the upper threshold for at least the first duration t1. When this is not the case, no event occurs, and the method ends in step 106. On the contrary, when it is determined in query step 104 that the pressure is below the lower threshold at least during the first duration t1, it is determined in the query step 108 that follows whether a pressure rise to the pressure above the upper threshold has occurred thereafter. When this is not the case, no event occurs, and the method ends in step 106. On the contrary, when the upper threshold is exceeded, an event occurs. It is then concluded that air bubbles have arrived in the system. Accordingly, the resetting of the integral component of the regulation scheme should now be performed.

[0067] However, for the case where air is present in the system, an infinite cycle of resetting the integral component should be avoided. To avoid this, the number of successive resettings is limited to a maximum value n max , for example max =3. The pressure regulator includes a counter which counts the number n of resets of the integral component which are performed successively. As long as the number n of resets which have been performed is less than a maximum value n max , the integral component is reset. In this regard, it is inquired in the query step 110 that n<nmax Is it true? When n<n max , a reset of the integral component of the control scheme is performed in step 112. In step 114, the number n of resets that have been performed is incremented by one.

[0068] However, if in query step 110 the query indicates that the number of resets n that have been performed is greater than or equal to the maximum value n max , then in step 116 the counter reading n indicating the number of resets that have been performed is reset to zero, and in step 118 all further resets are blocked for a second time duration t2. This second time duration t2 can be set, for example, to 30 seconds.

[0069] When an event is detected, a timer for the second duration t2 is started in step 120. This timer is queried in step 122. In query step 124, it is determined whether the time t that has elapsed since the occurrence of the event is greater than the second duration t2. If this is the case, the counter reading n indicating the number of resets that have been performed is reset to zero in step 126. From now on, another reset of the integral component of the control scheme can be performed again. The purpose of the time-dependent reset of the counter is to regard one or more air bubbles that enter the conveying device within the second duration of, for example, 30 seconds as an "event".

[0070] exist Figure 4 In the embodiment, the second time duration t2 used in step 118, during which the resetting of the integral component of the control strategy is prevented, corresponds to the second time duration t2 used in the query step 124, and the counter reading n is reset to zero again after the second time duration t2 used in the query step 124 has expired. As an alternative to this solution, different time lengths can also be used for preventing the resetting and for resetting the reset counter.

[0071] Figure 5 A pressure curve 128 , which shows the pressure in the supply line as a function of time, and a curve 130 , which shows the rotational speed of the delivery pump unit 54 as a function of time, are shown. Figure 5 It shows that the exhaust gas aftertreatment system is used Figure 4 130. The method shown in FIG. 131 shows how to react to the occurrence of air bubbles. Arrow 132 shows the time point at which the integral component of the control scheme is reset. It can be seen that at the time point shown by arrow 134, a stable pressure of the reactant in the range of ±400 hPa around the target value has been achieved.

[0072] The features disclosed in the preceding description, the claims and the drawings may be essential both individually and in any combination for realizing the invention in its various configurations.

Claims

1. A method for regulating the pressure in a pressurized supply line (18) for supplying a reactant for selective catalytic reduction to an exhaust gas flow (6) in an exhaust gas aftertreatment system, wherein: The exhaust gas aftertreatment system comprises: - a delivery pump (54) for delivering the reactants, a supply line (18) for supplying the reactant to the exhaust gas flow (6), wherein the supply line (18) is fluidically connected to the delivery pump (54), a pressure regulator (78) which is designed to set the delivery capacity of the delivery pump (54) as a function of the pressure of the reactant in the supply line (18) by means of a control strategy which has at least an integral component, The method comprises the following steps: - detecting the pressure of the reactant in the supply line (18), - detecting whether a pressure curve of the pressure of the reactant in the supply line (18) occurs which is characteristic of the presence of air bubbles in the reactant, The integral component is reset as a function of the detection of a pressure curve which is characteristic of the occurrence of air bubbles.

2. The method according to claim 1, characterized in that The control concept has a proportional component and an integral component.

3. The method according to any one of the preceding claims, characterized in that The pressure regulator (78) is designed to regulate the pressure of the reactant in the supply line (18) to a target value of the pressure.

4. The method according to any one of the preceding claims, characterized in that The pressure regulator (78) is designed to regulate the rotational speed of the delivery pump (54) as a function of the pressure of the reactant in the supply line (18).

5. The method according to any one of the preceding claims, characterized in that Detection of pressure trends that are characteristic of the presence of air bubbles includes: - detecting whether the pressure falls below a lower threshold value, in particular for a predefined period of time.

6. The method according to any one of the preceding claims, characterized in that Detection of pressure trends that are characteristic of the presence of air bubbles includes: - detecting whether the pressure initially falls below a lower threshold value for a predefined period of time and subsequently exceeds an upper threshold value for the pressure.

7. The method according to any one of the preceding claims, characterized in that The number of resets of the integral component that are performed successively is limited.

8. The method according to any one of the preceding claims, characterized in that The number of performed resets of the integral component is counted by means of a counter, wherein, if the number of performed resets exceeds a predefined maximum value, no further reset of the integral component is performed at least within a predefined second time period.

9. The method according to any one of the preceding claims, characterized in that If the number of performed resets exceeds a predefined maximum value, a time interval is initiated, wherein after the time interval has elapsed, the counter is reset for the number of performed resets.

10. The method according to any one of the preceding claims, characterized in that The exhaust aftertreatment system includes a storage tank (24) for the reactant.

11. A pressure regulator (78) for regulating the pressure in a pressurized supply line (18) for supplying a reactant for selective catalytic reduction to an exhaust gas flow (6) in an exhaust gas aftertreatment system, wherein: The exhaust gas aftertreatment system comprises a delivery pump (54) for delivering the reactant, which is fluidically connected to the supply line (18), wherein the pressure regulator (78) is designed to: - regulating the delivery capacity of the delivery pump (54) as a function of the pressure of the reactant in the supply line (18) by means of a control strategy, the control strategy having at least an integral component, - detecting a pressure curve of the pressure of the reactant in the supply line (18) which is characteristic of the presence of air bubbles in the reactant, and - Resetting the integral component is carried out as a function of the detection of a pressure curve which is characteristic of the occurrence of air bubbles.

12. An exhaust gas aftertreatment system for exhaust gas aftertreatment in an exhaust gas flow (6) by means of selective catalytic reduction, wherein: The exhaust gas aftertreatment system comprises: - a delivery pump (54) for delivering the reactants, a supply line (18) for supplying a reactant to the exhaust gas stream (6), wherein the supply line (18) is fluidically connected to the delivery pump (54), a pressure regulator (78) which is designed to regulate the delivery capacity of the delivery pump (54) as a function of the pressure of the reactant in the supply line (18) by means of a regulation strategy, the regulation strategy having at least an integral component, - wherein the pressure regulator (78) is designed to: - detecting a pressure curve of the pressure of the reactant in the supply line (18) which is characteristic of the presence of air bubbles in the reactant, and - Resetting the integral component is carried out as a function of the detection of a pressure curve which is characteristic of the occurrence of air bubbles.

13. Exhaust gas equipment for a motor vehicle, comprising an exhaust gas aftertreatment system according to claim 12.

14. Motor vehicle comprising an exhaust gas installation having an exhaust gas aftertreatment system according to claim 12.

Images