CN114294081A

CN114294081A - Method for emptying a fluid supply system

Info

Publication number: CN114294081A
Application number: CN202111157685.7A
Authority: CN
Inventors: P·佩利坎; M·克鲁瑟; R·凯普卡
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-10-08
Filing date: 2021-09-30
Publication date: 2022-04-08
Also published as: DE102020212722A1

Abstract

The invention relates to a method for emptying a fluid supply system (100) having a delivery unit (110), a delivery line (130), a pressure line (132) and a return line (134) having a non-return valve (154), the delivery unit (110) being connected to a fluid tank (120) via the delivery line, the delivery unit (110) being connected to a metering module (136) via the pressure line, the delivery unit (110) being connected to the fluid tank (120) via the return line, wherein the delivery unit (110) can be operated in a normal delivery direction such that a fluid (121) is sucked in via the delivery line (130) and delivered into the pressure line (132) and the return line (134) and the delivery unit can be operated counter to the delivery direction, wherein the delivery unit (110) is operated after a first preliminary emptying process (200)During a second emptying process, the metering module (136) is closed and the first power level (L) is applied in the conveying direction₁) And running until the preset standard is reached.

Description

Method for emptying a fluid supply system

Technical Field

The invention relates to a method for emptying a fluid supply system, for example an SCR supply system, as well as to a computing unit and a computer program for carrying out the method.

Background

DE 102016210262 a1 describes a method for emptying a fluid supply system, which is referred to herein as a reducing agent delivery system. Emptying is necessary to prevent the fluid or reducing agent from freezing in the lines or in the delivery unit when the associated vehicle is stopped or not in operation (freezing points may be, for example, -11 ℃ in the case of typical reducing agents such as urea).

Disclosure of Invention

According to the invention, a method for emptying a fluid supply system is proposed, as well as a computing unit and a computer program for carrying out the method, having the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the following description.

In the aftertreatment of exhaust gases in motor vehicles, the so-called SCR (Selective Catalytic Reduction) method can be used, in particular for reducing Nitrogen Oxides (NO)_x). Here, an aqueous urea solution (HWL) is introduced as a reducing agent solution into the exhaust gas, which is typically rich in oxygen.

For this purpose, a metering module or metering valve can be used as a component of the fluid supply system, which metering module or metering valve comprises an injection nozzle for injecting or entraining the aqueous urea solution into the exhaust gas stream. Upstream of the SCR catalyst, the aqueous urea solution reacts to ammonia, which in turn combines with nitrogen oxides on the SCR catalyst, producing water and nitrogen therefrom.

Typically, the metering valve is connected to the delivery unit via a pressure line. The pump of the delivery unit or the delivery pump pumps the aqueous urea solution from the reducing agent tank to the metering valve or the metering module. In addition, a return device is usually connected to the reducing agent tank, via which excess urea-water solution can be returned. A diaphragm or throttle in the reflux unit may control the reflux.

The invention relates to a method for emptying a fluid supply system, in particular an SCR supply system. The fluid supply system according to the invention has a delivery unit, which is connected to the fluid tank or the reducing agent tank via a delivery line, which is connected to the metering module via a pressure line, and a return line with a check valve, which is connected to the fluid tank via a return line. The return line can in particular branch off from the pressure line.

The conveying unit can be operated in a conventional conveying direction on the one hand, so that the fluid is sucked in via the conveying line (from the fluid tank) and conveyed into the pressure line (and then via the pressure line to the metering module). On the other hand, the delivery unit can however also be operated counter to the (normal) delivery direction, so that the fluid can be delivered back to the fluid tank via the delivery line. For this purpose, the delivery unit typically has a pump, for example a diaphragm pump or a piston pump, to which the delivery line and the pressure line are connected by means of one or more suitable valves. For example, a suitable switching valve can be provided, by means of which the pump can be switched between the supply line and the pressure line in such a way that fluid can be supplied in and against a (conventional) supply direction, while the pump itself can only provide one supply direction. However, it is also possible to consider actively controllable valves, by means of which the conveying direction can be reversed.

The invention is based on the idea of carrying out a first emptying process in which the supply line, the pressure line and the return line are emptied at least as well as possible, for emptying the fluid supply system, for example after the vehicle or its internal combustion engine has stopped. For this purpose, the transport unit can be operated against the normal transport direction in a simple case. However, the process described in DE 102016210262A 1 is also suitable, for which reference is expressly made to this document. In particular, the metering module or the metering valve is first closed, and the delivery unit is then operated counter to the normal delivery direction, whereby the fluid is returned from the delivery line and the delivery unit itself into the fluid tank. The metering module is then opened so that fluid also passes from the metering module, the pressure line and the return line into the fluid tank. The metering module is then switched off again and the delivery unit can be stopped or switched off.

It has turned out that in this way, although the fluid supply system can be emptied substantially and to a large extent, in some cases a certain amount of fluid may still remain in the pressure sensor or its cavity, which is typically arranged in the delivery unit, especially when the pressure sensor is arranged in the return line. It has been proven that a check valve in the return line makes an important contribution to this. Since the check valve remains closed during the mentioned (first) emptying procedure.

Against this background, it is now within the framework of the proposed invention that the second emptying process is carried out after the first mentioned emptying process. In this case, after it has possibly been switched on again, the delivery unit is operated in a second emptying process with the metering module closed and in the delivery direction at or with the first power level until a predefined criterion is reached. The first power stage has a power of in particular between 2% and 40%, preferably between 5% and 30%, further preferably between 5% and 15% of the maximum power of the delivery unit. Particularly suitably, for example, 10% of maximum power. Such a (relatively) small power level also means a relatively small delivery flow provided by the delivery unit, with which air is delivered from the delivery unit into the return duct (fluid has been removed from the duct and the delivery unit in the first emptying procedure, so that there is only air therein). The return line up to the non-return valve can also be referred to as a return channel, on which a pressure sensor, for example, is then arranged.

The predetermined criterion is in particular selected such that the check valve is opened by an overpressure in the return line when the criterion is reached. That is, the pressure is increased by operating the delivery unit until the check valve opens (the metering valve is closed). As a result, fluid that may still be present in the return line is conveyed via the return line into the fluid tank and, in particular, fluid that may be present in the pressure sensor is removed therefrom as shown.

In this process, it is important to note that, although the pressure is increased such that the non-return valve opens, as far as possible no fluid is sucked from the fluid tank into the delivery unit. This can be achieved, for example, by monitoring the mentioned criteria in a suitable manner. The predetermined criterion here preferably includes a pressure drop in the fluid supply system. A pressure drop (pressure is known, for example, by means of the already mentioned pressure sensor) means that the opening pressure of the check valve is reached or exceeded, as a result of which air together with possible fluid can escape, as a result of which the pressure drops particularly quickly. In this connection, it is possible to take into account, for example, the determination of a certain gradient of the pressure, which gradient is reached when a significant pressure drop is detected.

It is also expedient if the predetermined criterion comprises the end of a predetermined period of time. The time period may then be predefined, in particular, depending on the volume of the fluid supply system and the first power level. If it is known how much volume flow the delivery unit provides and how much volume is present in the delivery unit and the important pipes in which there may be air compressed, it can be determined how long the delivery unit has to be operated until a sufficiently high pressure is generated such that the check valve opens.

With the proposed procedure, not only the pipes and the delivery unit themselves can be better emptied, but also fluids that may be present in the pressure sensor or its cavity can be removed, whereby damage by frozen fluids at low temperatures can be less and thus the life of the components can be increased.

After or since the predetermined criterion has been reached, the conveying unit is then preferably still operated against the conveying direction, and in particular at or for a second power level which is higher than the first power level. Suitably, the second power stage has a power of between 2% and 60%, preferably between 5% and 40%, further preferably between 25% and 35% of the maximum power of the delivery unit. Particularly suitably for example 30% of maximum power. In this way, fluid which could be sucked into the delivery line during operation of the delivery unit at the first power level can be removed from the delivery line again and returned to the fluid tank.

After that, for example when the pressure again reaches the value before or at the beginning of the second emptying process, the power of the delivery unit can be reset to zero, can be set back to the normal delivery direction (for example by switching the respective changeover valve) as a preparation for the next normal delivery operation, and then the delivery unit can be completely switched off. It is also conceivable to carry out the second emptying process several times, if this proves to be expedient.

The computing unit according to the invention, for example a control device of a motor vehicle, such as a motor control device or an exhaust gas aftertreatment control device, is provided in particular in a programmed manner for carrying out the method according to the invention.

It is also advantageous to implement the method according to the invention in the form of a computer program or a computer program product having program code for executing all method steps, since this results in particularly low costs, in particular if the implemented control device is also used for other tasks and is therefore already present. Suitable data carriers for supplying the computer program are, in particular, magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs and others. The program may also be downloaded via a computer network (internet, intranet, etc.).

Further advantages and designs of the invention emerge from the description and the drawings.

Drawings

The invention is presented schematically with the aid of embodiments in the drawings and will be described below with reference to the drawings.

Fig. 1 schematically shows a fluid supply system in which a method according to the invention can be carried out;

fig. 2 schematically shows the flow of the method according to the invention in a preferred embodiment;

fig. 3 shows schematically in a preferred embodiment the pressure profile and the control profile of a transport unit using the method according to the invention.

Detailed Description

In fig. 1, a fluid supply system 100 is schematically shown, with which a method according to the invention can be carried out. The fluid supply system 100 is in particular designed as an SCR system and comprises a delivery unit 110 which has a pump or delivery pump 140 and a directional valve (Wegeventil) 142 and is provided for sucking the reducing agent 121 (or reducing agent solution) as a fluid to be delivered out of a fluid tank or reducing agent tank 120 via a delivery line 130 in a conventional delivery direction and delivering it to a metering module or metering valve 136 via a filter 150 and a pressure line 132. Where the reducing agent 121 is then injected into the exhaust line 170 of the internal combustion engine.

Furthermore, the fluid supply system 100 comprises a return line 134 branching off from the pressure line 132, via which the reducing agent can be conducted back from the system into the reducing agent tank 120. In the return line 134, in addition to a diaphragm or throttle 152 providing a partial flow resistance, a check valve 154 having a specific opening pressure is provided.

Furthermore, a pressure sensor 144 is provided, which is provided for measuring the pressure in the return line in a section (also referred to as return line) there before the check valve 154. A computing unit 160, which is designed, for example, as an exhaust gas aftertreatment control device, is connected to the pressure sensor 140 and receives information from the pressure sensor about the pressure in the respective line. In addition, the exhaust gas aftertreatment control device 160 is connected to the delivery unit 110, in particular to the pump 140, and to the metering module 136, so that it can be actuated.

The conveying direction of the conveying unit 110 can be reversed by actuating the switching valve 142, so that fluid can be conveyed into the reducing agent tank 120 via the conveying line 130 counter to the normal conveying direction.

Fig. 2 schematically shows the flow of the method according to the invention in a preferred embodiment, and fig. 3 schematically shows the pressure profile and the actuation profile of a conveying unit using the method according to the invention in a preferred embodiment, where p indicates the pressure (in one example) in mbar, L indicates the power of the conveying unit (in one example) or of the pump, and S indicates the position of the reversing valve, and the profiles are each plotted over time t. Fig. 2 and 3 will be described generally later.

First, a first evacuation process 200 is performed in the fluid supply system, for example, after the internal combustion engine is stopped. As already mentioned, this first emptying process can be carried out, for example, as described in DE 102016210262 a 1. The first emptying process typically ends with the switching off of the delivery unit and the closing of the metering module.

A second evacuation process is then performed, which includes, for example,

subsequent steps

210, 220, 230, and 240.

First, according to step 210, at a point in time t₁The delivery unit is supplied with a first power level (or "duty cycle") L of, for example, 10%₁In operation, and in the normal conveying direction, that is to say with the position S of the diverter valve at 0, the metering module remains closed. If this is not already the case, the metering module is switched off accordingly. The air present in the supply line is then pumped into the return line — but also in particular into the pressure sensor or its cavity. However, as far as possible no fluid is sucked in here, in any case not pumped into the pressure line or the return line.

This procedure is carried out until a predetermined criterion is reached. As already mentioned, the criterion includes, for example, pressure drop or duration. This can be seen in FIG. 3 from time t₁The starting pressure p rises because the metering module is closed and the check valve is closed anyway at the beginning. However, once the cracking pressure of the check valve is reached (about 70mbar in the example shown), the check valve opens, air escapes together with possible fluid in the pressure sensor or in its cavity and the pressure p drops rapidly. A specific gradient G of the pressure p is plotted by way of example, and the criterion can be regarded as fulfilled or reached, for example, when the gradient is reached. At a point in time t₂This is the case.

But can equally be calculated from the point in time t₁Until a time t₂And taking into account the duration of time at power level L₁The volume flow of the delivery unit and the volume of air to be pumped or transported. For this reason, knowledge about the volume of the fluid supply system is necessary, but may for example simply be measured or otherwise known for a specific fluid supply system or a specific type.

According to step 220, at a point in time t₂And the conveying direction of the conveying unit is reversed by switching the reversing valve and enabling the pose S to take a value of 1. At the same time or possibly after a short time, the delivery unit is then brought to a higher power level L of, for example, 30%₂And (5) operating. In this way, the fluid possibly present in the delivery conduit and previously sucked up is again delivered back into the fluid tank, the pressure being further reduced.

According to step 230, at a point in time t₃When the pressure has, for example, reached the point in time t again₁At the previous or previous starting value, the power of the transmission unit is set back to zero, L =0, and then the time t is reached according to step 240₄The entire conveying unit is disconnected and the switching valve 142 is switched back to the normal conveying direction for the preparation for subsequent use, S = 0.

Optionally, it is also possible to reach the criterion at a time t₂The power of the conveyor unit (after which the conveyor direction is adjusted to normal, i.e. the position S has the value 0) is set back to zero according to step 231, and then the procedure can be continued again as before in step 240.

With the proposed method, the fluid supply system, in particular the pressure sensor or its cavity, can thus be emptied particularly effectively, so that possible damage by frost is prevented.

Claims

1. Method for emptying a fluid supply system (100) having a delivery unit (110), a delivery line (130), via which the delivery unit (110) is connected to a fluid tank (120), a pressure line (132), via which the delivery unit (110) is connected to a metering module (136), and a return line (134) with a check valve (154), via which the delivery unit (110) is connected to the fluid tank (120),

wherein the delivery unit (110) is operable in a normal delivery direction such that a fluid (121) is sucked in via the delivery line (130) and delivered into the pressure line (132) and into the return line (134), and wherein the delivery unit is operable counter to the delivery direction,

wherein the delivery unit (110) is brought to a first power level (L) in the delivery direction after a first preliminary emptying process (200) and in a second emptying process with the metering module (136) closed₁) And running until the preset standard is reached.

2. Method according to claim 1, wherein the conveying unit (110) is operated counter to the conveying direction since the predefined criterion has been reached in the second emptying process, in particular at a second power level (L) which is higher than the first power level₂）。

3. Method according to claim 2, wherein said second power level (L)₂) Is a power between 2% and 60%, preferably between 5% and 40%, further preferably between 25% and 35% of the maximum power of the delivery unit (110).

4. Method according to any of the preceding claims, wherein the first power level (L)₁) Is a power between 2% and 40%, preferably between 5% and 30%, further preferably between 5% and 15% of the maximum power of the delivery unit (110).

5. Method according to one of the preceding claims, wherein the predefined criterion is selected such that the non-return valve (154) is opened already by an overpressure in the return valve (134) when the predefined criterion is reached.

6. The method according to claim 5, wherein the predetermined criterion comprises a pressure drop in the fluid supply system (100).

7. According to claim5 or 6, wherein the predetermined criterion comprises the end of a predetermined period of time, in particular as a function of the volume of the fluid supply system (100) and the first power level (L)₁) Is predetermined.

8. A computing unit (150) which is set up to carry out all method steps of the method according to one of the preceding claims.

9. Computer program which, when being implemented on a computing unit (160), causes the computing unit (160) to carry out all method steps of the method according to any one of claims 1 to 7.

10. A machine-readable storage medium having stored thereon the computer program according to claim 9.