SE540367C2 - System and method for evacuating fluid in pipelines in a vehicle - Google Patents

Abstract

The invention relates to a system for evacuating fluid in a vehicle, the system comprising: a first tank (4) intended for pressurized air, a second tank (5) intended for a fluid to be supplied to a fluid dosing unit (20), a valve device (11), and a plurality of fluid paths. The system is arranged to be in a first state in response to a control signal, in which the valve device (11) is in a first position, the fluid being transferred from the second tank (5) to the fluid dosing unit (20) and pressurized air filling the first tank ( 4), or a second condition, in which the valve device (11) is in a second position and the fluid paths are blown clean of fluid. The invention also relates to a method for evacuating fluid in a system intended for a vehicle.

Description

FIELD OF THE INVENTION The present invention relates to a system and method for evacuating fluid in a vehicle. The invention also relates to a vehicle, a computer program and a computer program product.

Background of the invention A common feature of modern vehicles is to transfer a quantity of fluid from a tank to a dosing device for subsequent dosing via a pipeline and by means of a pump. An example of the above is the supply of fuel to a fuel pump for subsequent injection into the cylinder of an internal combustion engine. Another example, particularly relevant for commercial vehicles such as trucks, buses and construction machinery, is the supply of reducing agents to the dosing system for subsequent injection into the diesel engine's exhaust system.

When the transfer of fluid has been completed, fluid can remain both in the pipeline connecting the tank and the dosing unit and in the dosing unit itself.

This residual fluid can pose a fire hazard, especially if the fluid is flammable, such as vehicle fuel, and the vehicle is used for special purposes, such as military vehicles or fire engines.

In addition, at low temperatures, the remaining fluid may freeze and clog the pipeline. A blockage in pipelines which arises in this way is normally avoided by keeping the pipelines warm, preferably by means of electrical coils. However, this solution has several disadvantages, such as increased technical complexity in the system and increasing energy consumption. Clogging of the pipelines can also take place at higher temperatures. This occurs in particular when the fluid, eg reducing agent, is left in the pipeline for a long time and crystallizes.

In addition, it is not uncommon for the fluid, especially when in the liquid phase, to have corrosive properties and thus, on prolonged contact, can corrode the pipeline it is in, leak out and damage surrounding metallic components. It is also known that components of electric heating systems, such as electric coils, often experience short circuits caused by fluids with corrosive properties, such as reducing agents.

US2012 / 0031073A1 discloses a device for supplying reducing agents to a vehicle's exhaust system. The device comprises a pump arranged between a working tank and a storage tank as well as a reducing agent dispenser which is connected to the working tank via a pipeline. During engine operation, the reducing agent is pumped from the working tank to the dispenser. After stopping the motor, the effect of the pump causes unused reducing agent to be returned to the working tank from both the reducing agent dispenser and the pipeline.

The solution described in US2012 / 0031073A1 thus assumes that the device comprises a pump which is in operation even when the motor is switched off. This condition, called "after run" in English, should be avoided to minimize the vehicle's energy consumption and allow the main switch to be switched off immediately after driving. In addition, the design solution with a reversible pump makes it impossible to use non-return valves and consequently requires a two-tank system so that the pump does not wear out prematurely.

The device is thus relatively complex. In addition, control of such a device, including a pump and two fluid tanks, becomes complicated.

The object of the present invention is thus to provide a technically simple solution with as few components as possible, and which in particular removes residual fluid from the pipelines and / or the dosing unit in an energy-efficient manner.

Summary of the invention According to a first aspect, the object described above is achieved at least in part by a system for evacuating fluid in a vehicle according to claim 1.

The system thus comprises a first tank intended for pressurized air, a second tank intended for a fluid to be supplied to a fluid dosing unit, a valve device, a first fluid path connecting a source of compressed air to the ventilation device, a second fluid path connecting a third fluid path connecting the second the tank with the valve device, a fourth fluid path connecting the valve device to the fluid dosing unit, the system in response to a control signal being arranged to be put in a first state, in which the valve device is in a first position in which pressurized air flows from the compressed air source to the first tank and through the first and second fluid paths, and the fluid flows from the second tank to the fluid metering unit via the valve device and through the third and fourth fluid paths, or a second state, in which the valve device is in a second position in which pressurized air flows from the first tank to the fluid dosing unit via the valve device and through the second and the fourth fluid path, and to the second tank via the valve device, and through the second, the third and a part of the fourth fluid path.

The system according to the invention comprises a valve device which alternates between two positions, a first position where the fluid is supplied to the dosing unit and the first tank is filled with pressurized air and a second position where the fluid paths, i.e. the pipelines transporting the fluid, as well as the dosing unit are blown clean. The purge is performed only with pressurized air supplied to the system at the same time as the fluid was supplied to the dosing unit. This achieves a simple and efficient design solution. In addition, the design and stretching of the respective fluid path and the positioning of the valve device mean that in the purge position a fluid connection is created between the second, the third and the fourth fluid path. Then pressurized air from the first tank can flow through both the third and the fourth fluid path. The remaining fluid from the third fluid path is then returned to the second tank. The air flowing through the fourth fluid path means that also this fluid path and the dosing unit which is arranged in connection with the outlet of the path are emptied of remaining fluid, which is then, in a variant, returned to the second tank. This eliminates the need for a dedicated, energy consuming system component, such as a pump, to return residual fluid to the fluid tank.

According to a second aspect, the object described above is achieved at least in part by a method for evacuating fluid in a system intended for a vehicle, the system comprising a first tank intended for pressurized air, a second tank intended for a fluid to be supplied to a fluid dosing unit , a valve device, a first fluid path connecting a source of compressed air to the valve device, a second fluid path connecting the valve device to the first tank, a third fluid path connecting the second tank to the valve device, a fourth fluid path connecting the valve device to the fluid metering unit, the method comprising receiving a control signal and, in response to the control signal, placing the system in a first state, in which the valve device is in a first position in which pressurized air flows from the compressed air source to the first tank via the valve device and through the first and second fluid path, and the fluid flows from the other tank to the fluid dosing unit via the valve device and through the third and fourth fluid path, or in a second state, in which the valve device is in a second position in which pressurized air flows from the first tank to the fluid dosing unit via the valve device and through the second and fourth fluid path , and to the second tank via the valve device, and through the second, the third and a part of the fourth fluid path.

According to a third aspect, the object is achieved at least in part by a computer program, P, wherein said computer program P comprises program code for causing a computer unit to perform the steps according to the method.

According to a fourth aspect, the object is achieved at least in part by a computer program product comprising a program code stored on a computer-readable non-volatile medium for performing the method steps, when said program code is executed on a computer unit.

According to a fifth aspect, the object is achieved at least in part by a vehicle which comprises the system according to the invention.

Various embodiments are described in the dependent claims and in the detailed description.

Brief description of the accompanying figures The invention will be described below with reference to the accompanying figures, of which: Fig. 1 is a schematic top view of a vehicle comprising tanks intended for air and reducing agent, respectively, and reducing agent dispensers.

Fig. 2a shows a block diagram representing a fluid evacuation system according to an embodiment of the present invention where the system is in a first state.

Fig. 2b shows a block diagram representing the system in a second state. Fig. 3 is a flow chart containing the method steps according to an embodiment of the present invention.

Detailed Description of Preferred Embodiments of the Invention Fig. 1 is a schematic top view of a vehicle. The vehicle 1 is shown here in the form of a truck or tractor with a chassis 9 and two pairs of wheels 10A and 10B. The truck is shown here only as an example, and the vehicle 1 can instead be, for example, a city jeep, a work vehicle or the like. A cab 7 is located at the front of the truck. An internal combustion engine 41 is located under the cab 7. The exhaust gases generated during the combustion process are led into an exhaust system 42. Tanks 4, 5 intended for pressurized air and reducing agents are also mounted on the chassis 9. Trucks and other commercial vehicles typically have a pneumatic braking system comprising a tank 14 containing pressurized air. As shown in Fig. 1, the air tank 14 is also normally mounted on the chassis 9. In one embodiment, the air tank 14 of the braking system can be used as a source of compressed air. Then the pressurized air is supplied to the tank 4 via a pipeline 53.

A reducing agent dispenser 47 is typically provided in the exhaust stream downstream of the internal combustion engine 41. More specifically, the reducing agent dispenser 20 is often located in a muffler 43 normally provided in connection with the exhaust system 42. A tank 5 supplies the reducing agent dispenser 20 with the reducing agent dispenser 20. injects at least a portion of the added reducing agent into the exhaust gas stream in order to help reduce emissions of harmful nitrogen oxides. In one embodiment, the reducing agent flows in a closed circuit. This embodiment also comprises a return pipeline 21 via which unused reducing agent is returned to the reducing agent tank 5. In this context, in Europe the product name AdBlue <®> is usually used when referring to reducing agents. Reducing agents are used here only for exemplary purposes and the tanks may instead contain other relevant fluids, such as diesel fuel. At least the second tank 5 is provided with at least one sensor (not shown in Fig. 1) which measures the amount of reducing agent in the tank 5. The sensor can for example be a level sensor, ie. a device that measures fluid level in the tank, or a device that determines the weight or volume of the fluid. Normally this tank 5 holds about 80 liters of reducing agent while the tank 4 intended for pressurized air holds about 10 l. The second tank 5 may also be provided with a valve, preferably a non-return valve, which opens when the internal pressure in the tank 5 exceeds one predetermined value. The transfer of reducing agent is normally controlled by a control unit 19 shown schematically in Fig. 1. As mentioned above, it is desirable to keep the pipeline and the dispenser itself free of reducing agent when the transfer is interrupted. For this, a system 100 is used, which will now be explained with reference to Figures 2a-2b.

Fig. 2a shows a block diagram representing a system 100 for evacuating fluid, such as reducing agent, where the system 100 is in a first state. The system 100 comprises a first tank 4 intended for pressurized air and a second tank 5 intended for reducing agent to be supplied to a reducing agent dispenser 20 and a valve device 11. Fluid paths in the form of pipelines extend so that a first pipeline 13 connects a compressed air source 14 to the valve device 11, a second pipeline 15 connects the valve device 11 to the first tank 4, a third pipeline 17 connects the second tank 5 to the valve device 11 and a fourth pipeline 18 which connects the valve device 11 to the reducing agent dispenser 20. In particular the pipelines 13, 15, 17, 18 , but also the tanks 4, 5 and / or the fluid dosing unit 20, may be made of materials which are resistant to the corrosive properties of the reducing agent and / or internally coated with a suitable anticorrosive substance.

The valve device 11 may be a five-port valve, for example a 5/2 valve shown in Fig. 2a. The valve device can be operated in different ways, for example by means of a solenoid and / or a spring device (not shown). Alternatively, a 5/3 valve can be used. The number combination 5/2 indicates that the valve has five ports, ie. openings in the valve housing, and two positions. Referring to the five-port valve shown in Fig. 2a, three of the ports, first 22, second 24 and third 26, are arranged on the valve side facing the reducing agent dispenser 20. On the opposite valve side, fourth 28 and fifth ports are provided. Depending on the position of the valve, the ports 22, 24, 26, 28, 30 serve as inlets and outlets for air and / or reducing agents, respectively.

Still referring to Fig. 2a, the system 100 is shown in a first, active state, which means that the valve device 11 is in a first position. A segment of the first pipeline 13 extends from an air source 14 to a pressure control device 23. This device 23 can be realized as a valve, preferably a pressure-operated valve. A further segment of the first pipeline 13 extends between the pressure control device 23 and the third port 26 of the five port valve. The third 26 and the fifth valve port are in fluid communication so that the compressed air flowing in the first pipeline 13 can flow through the second pipeline 15 to finally reach the first thought 4.

In the first position, the second 24 and the fourth 28 ports are also in fluid communication. This causes the reducing agent to be pumped out of the second tank 5, flows through the third pipeline 15 and enters the valve device 11 via the fourth valve port 28. The fourth pipeline 18 of the system, which extends between the valve device 11 and the reducing agent dispenser 20, comprises according to one embodiment a main pipeline 180 which at a branch point FP branches into a first 181 and a second 182 pipeline branch. The branch 181 connects the branch point FP and the second port 24 of the valve device 11 while the branch 182 connects the branch point FP and the first port 22 of the valve device 11. As previously mentioned, the second 24 and the fourth port 28 are in fluid communication. Accordingly, the reducing agent flows through the first pipeline branch 181 and the main pipeline 180 to eventually reach the reducing agent dispenser 20. The first valve port 22 is closed in this position. In summary, the reducing agent can be transferred from the second tank 5 to the dispenser 20 whose location and function are described in connection with Fig. 1. This takes place via the valve device 11 and through the third 17 and a part of the fourth pipeline 18. In parallel with this process it is filled the first tank 4 with pressurized air until the pressure in the tank 4 exceeds a predetermined value.

In the embodiment shown in Fig. 2a, the system also comprises a fifth pipeline 21 which connects the dispenser 20 to the second tank 5 so that reducing agent flows in a closed circuit consisting of the third pipeline 17, the first branch 181 and the main pipeline 180 belonging to the fourth pipeline 18, and the fifth pipeline 21. This configuration means that unused reducing agent is returned to the second tank 5. Unused reducing agent can then be used as refrigerant. In addition, a quantification of this return flow can be used to find out whether the supply of reducing agent to the dispenser 20 works as planned. In an alternative embodiment (not shown) which enables a simpler construction solution, the system 100 lacks the fifth pipeline 21 and the excess reducing agent is disposed of in another way.

The compressed air of the system can be delivered from an air tank 14 mounted on the vehicle. In one embodiment, the pressurized air source is the air tank which is part of the vehicle's pneumatic braking system and which is described in connection with Fig. 1. Thanks to the robust construction solution, the size of the pressure is not of primary importance as long as the pressurized air can empty the pipes and dispenser. . SUVs and other vehicles that do not have their own air tank can be equipped with an air compressor that provides compressed air. Alternatively, the compressed air may consist of / include exhaust gases produced in the vehicle's exhaust system.

In Fig. 2b, the system 100 is in a second, active state and the valve device 11 is in a second position. Stretching and design of the pipelines 13, 15, 17, 18 is unchanged compared to Fig. 2a. The first 22 and the fourth 28 and the second 24 and the fifth valve port, respectively, are in fluid communication. This means that the pressurized air from the first tank 4 via the valve device 11 flows through the second pipeline 15 and the first pipeline branch 181 to the branch point FP after which a first part of the pressurized air flows through the second pipeline branch 182, passes the valve device 11, and reaches via the third pipeline 17 finally the second tank 5. The remaining fluid from the second pipeline branch 182 and the third pipeline 17 is then returned to the second tank 5. At the same time a second part of the pressurized air flows from the branch point FP to the fluid dosing unit 20 through the main pipeline 180 belonging to the fourth 18 pipeline. This means that the first pipeline branch 181, the main pipeline 180 and the dispenser 20 arranged in connection with the main pipeline are also emptied of residual fluid, which is then, in an embodiment shown in Figs. 2a and 2b, returned to the second tank 5. the third valve port 26 is closed in this position.

The system 100 changes state in response to a control signal. More specifically, an electronic control unit 19 may be arranged to generate a first control signal for placing the system 100 in the first state and a second control signal for placing the system 100 in the second state. In one embodiment, the control unit 19 generates a first control signal when the vehicle's engine is started. The first control signal activates the valve device 11 which assumes a first position whereupon reducing agent begins to be transferred to the dispenser 20 and the first tank 4 is filled with pressurized air until the pressure in the tank 4 exceeds a predetermined value as described above in connection with Fig. 2a.

In another, adjacent embodiment, the control unit 19 generates a second control signal when the engine of the vehicle is switched off. The second control signal activates the valve device 11 which assumes a second position whereupon the pipelines 17, 18 are blown clean as described above in connection with Fig. 2b. Alternatively, the valve device 11 which is operated with mechanical and electrical actuation when the engine is switched off, i.e. when there is no current in the system, it is moved to a second position by a purely mechanical actuation. This is typically accomplished by applying a force by means of a spring. The counterforce, which is normally generated by the electric actuator, for example a solenoid, is absent when the motor is switched off and the system has lost power. This causes the valve device 11 to turn so that the pressurized air in the first tank 4 begins to flow. According to one embodiment, the control unit 19 is arranged to also control the pressure control device 23.

The control unit 19 may be an integral part of the system 100. The control unit 19 further comprises a processor unit 29 and a memory unit 39 which is connected to the processor unit 29. On the memory unit 39 a computer program P is stored, which can cause the control unit 19 to perform the steps according to the method described. here in. According to one embodiment, the memory unit 39 is part of the processor unit 29. The processor unit 29 may consist of one or more CPUs (Central Processing Unit). The memory unit 39 may comprise a non-volatile memory, for example a flash memory or a RAM (Random Access Memory). The memory unit 39 includes instructions for causing the processor unit 29 to execute the method steps described herein.

According to one embodiment, the control unit 19 is arranged to put the system 100 in the second state for a predetermined period of time, for example 10, 20, 30 or 40 seconds.

In addition, the system 100 may be arranged to be placed in a passive state (not shown), which means that no fluid, i.e. neither reducing agent nor pressurized air is transferred between the second tank 5 and the reducing agent dispenser 20.

The control unit 19 and the unit / units actuating the valve device 11 and the pressure control device 12 can, for example, communicate with each other through a bus, for example a CAN bus (Controller Area Network) which uses a message-based protocol. Examples of other communication protocols that can be used are TTP (Time-Triggered Protocol), Flexray and others. In this way, signals and data described above can be exchanged between different units in the vehicle 1. For example, signals and data can instead be transmitted wirelessly between the different units.

Fig. 3 is a flow chart containing the method steps of the present invention. The flow chart shows a method of transferring fluid into the system 100 as previously described with reference to Figures 2a and 2b. The method comprises receiving a control signal and, in response to the control signal, placing the system in a first state 70 or in a second state 80.

In a first state 70, a first valve device 11 is in a first position. In this state 70, reducing agent flows from a second tank 5 to a fluid metering unit, i.e. a reducing agent dispenser 20, via the valve device 11 and through a third 17 and a fourth 18 fluid path, i.e. pipeline.

Reducing agent which is hereby transferred to the fluid dosing unit, i.e. the dispenser 20 is used for injection into the vehicle's exhaust system. At the same time, pressurized air flows from a compressed air source 14 to a first tank 4 via the valve device 11 and through the first 13 and the second 15 pipeline, according to Fig. 2a. The first tank 4 is filled with pressurized air until the pressure in the tank 4 exceeds a predetermined value.

In a second condition 80, in which the valve device 11 is in a second position in which pressurized air flows from the first tank 4 to the fluid dosing unit 20 via the valve device 11 and through the second 15 and the fourth 18 fluid path. The compressed air also flows to the second tank 5 via the valve device 11, and through the second 15, the third 17 and a part of the fourth 18 the fluid path. As mentioned above, the fluid paths are in the form of pipelines 13, 15, 17, 18 and their design and extension are the same regardless of condition. The design and stretching of the respective fluid path 13, 15, 17, 18 and the positioning of the valve device 11 means that in the second state 80 a fluid connection is created between the second 15, the third 17 and the fourth 18 fluid path. Then pressurized air from the first tank 4 can flow through both the third 17 and the fourth 18 fluid path. The remaining fluid from the third 17 fluid path is then returned to the second tank 5. The air flowing through the fourth 18 fluid path means that also this fluid path and the dispenser 20 which is arranged in connection with the outlet of the path are emptied of remaining fluid.

The present invention is not limited to the embodiments described above. Various alternatives, modifications and equivalents can be used. Therefore, the above-mentioned embodiments do not limit the scope of the invention, which is defined by the appended claims.

Claims (22)

Patent claims A system (100) for evacuating fluid in a vehicle (1), the system comprising: - a first tank (4) intended for pressurized air, - a second tank (5) intended for a fluid to be supplied to a fluid dosing unit (20), - a valve device (11), - a first fluid path (13) connecting a source of compressed air (14) to the valve device (11), - a second fluid path (15) connecting the valve device (11) to the first tank (4 ), - a third fluid path (17) connecting the second tank (5) to the valve device (11), - a fourth fluid path (18), comprising a first part (181) which at a branch point (FP) branches into a main fluid path (180), which connects a second port (24) in the valve device (11) to the fluid dosing unit (20), and a second fluid path branch (182), which connects the second port (24) in the valve device (11) to a first port (22). ) in the valve device (11), characterized in that the system (100) is arranged in response to a control signal to provide in a first state, in which the valve device (11) is in a first position in which pressurized air flows from the compressed air source (14) through the first fluid path (13) via the valve device (11) through the second fluid path (15) to the first tank (4), and the fluid flows from the second tank (5) through the third fluid path (17) via the valve device (11) through the fourth fluid path (18) to the fluid dosing unit (20), or in a second state where the fluid paths transporting the fluid are blown clean, in which the valve device (11) is in a second position in which pressurized air flows from the first tank (4) through the second (15) fluid path via the valve device (11) through the main fluid path (180) to the fluid dosing unit (20), and from the first tank (4) through the second (15) fluid path, via the valve device (11), through the first part of the fourth fluid path (181) through the second fluid path branch (182) via the valve device (11) through the third f luidbanan (17) to the second tank (5). The system (100) according to claim 1, wherein, when the system is in the second state, pressurized air flows from the first tank (4) via the valve device to the branch point (FP) after which a first part of the pressurized air flows via the valve device to the second tank (5) through the second fluid path branch (182) and the third fluid path, and a second portion of the pressurized air flows to the fluid metering unit (20) through the main fluid path (180). The system (100) of claim 1 or 2, wherein the system further comprises a fifth fluid path (21) connecting the fluid metering unit (20) to the second tank (5) so that the third fluid path (17), the first fluid path branch (181) and the main fluid path (180) belonging to the fourth fluid path (18), and the fifth fluid path (21) forming a closed circuit. The system (100) according to any one of the preceding claims, in which the valve device is arranged to be operated by mechanical and electrical actuation, and wherein the valve device (11), when the engine of the vehicle is switched off, is arranged to be moved into the second position by a mechanical actuation , preferably by means of a spring, so that the pressurized air in the first tank (4) begins to flow. The system (100) according to any one of the preceding claims, wherein the valve device (11) is a five-port valve, preferably a 5/2 or a 5/3 valve. The system (100) of any preceding claim, wherein the fluid provided is a reducing agent. The system (100) according to any one of the preceding claims, comprising a pressure control device (23) arranged in the first fluid path (13) between the compressed air source (14) and the valve device (11). The system (100) according to any of the preceding claims, comprising a control unit (19) arranged to generate a first control signal to put the system in the first state and a second control signal to put the system in the second state. The system (100) of claim 8, wherein the control unit (19) is arranged to control the pressure control device. The system (100) of claim 8 or 9, wherein the control unit (19) is arranged to generate a first control signal when the engine of the vehicle is started. The system (100) according to any one of claims 8-10, wherein the control unit (19) is arranged to generate a second control signal when the engine of the vehicle is switched off. The system (100) according to any one of claims 8-11, wherein the control unit (19) is arranged to put the system in the second state for a predetermined period of time. A vehicle (1) comprising the system (100) according to any one of the preceding claims. A method of evacuating fluid in a system (100) intended for a vehicle (1), the system (100) comprising: - a first tank (4) intended for pressurized air, - a second tank (5) intended for a fluid to be supplied to a fluid dosing unit (20), - a valve device (11), - a first fluid path (13) connecting a source of compressed air (14) to the valve device (11), - a second fluid path (15) connecting the valve device (11 ) with the first tank (4), - a third fluid path (17) connecting the second tank (5) to the valve device (11), - a fourth fluid path (18), comprising a first part (181) as in a branch point ( FP) branches into a main fluid path (180) connecting a second port (24) of the valve device (11) to the fluid metering unit (20), and a second fluid path branch (182) connecting the second port (24) of the valve device (11) with a first port (22) in the valve device (11), characterized in that the method comprises - receiving (50) a piece dizziness signal - in response to the control signal, to put (60) the system in a first state, in which the valve device (11) is in a first position in which pressurized air flows from the compressed air source (14) through the first fluid path (13) via the valve device (11 ) and through the second fluid path (15) to the first tank (4), and the fluid flows from the second tank (5) through the third fluid path (17) via the valve device (11) through the fourth fluid path (18) to the fluid dosing unit (20). ), or a second condition in which the fluid paths transporting the fluid are blown clean, in which the valve device (11) is in a second position in which pressurized air flows from the first tank (4) through the second (15) fluid path via the valve device (11) and through the main fluid path (180) to the fluid metering unit (20), and from the first tank (4) through the second (15) fluid path via the valve device (11) through the first portion of the fourth fluid path (181) through the second fluid path the branch (182) via the valve device (11) through the third fluid path (17) to the second tank (5). The method according to claim 14, wherein when the system is in the second state, the method comprises - allowing pressurized air from the first tank (4) to flow via the valve device (11) to the branch point (FP), - then allowing a first part of the pressurized air via the valve device (11) flow to the second tank (5) through the second fluid path branch (182) and the third fluid path (17), and at the same time - allow a second part of the pressurized air to flow to the fluid dosing unit (20) through the main fluid path (180). The method of any of claims 14-15, comprising controlling the pressure of the pressurized air in the first fluid path. The method of any of claims 14-16, comprising generating a first control signal to put the system in the first state or a second control signal to put the system in the second state. The method of claim 17, comprising generating a first control signal when the vehicle's engine is started. The method of any of claims 17-18, comprising generating a second control signal when the vehicle's engine is turned off. The method of any of claims 14-19, comprising placing the system in the second state for a predetermined period of time. Computer program (P), wherein said computer program (P) comprises program code for causing an electronic control unit (19), or other computer connected to the electronic control unit, to perform the steps according to any one of claims 14-20. A computer program product comprising a program code stored on a computer readable non-volatile medium for performing the method steps according to any one of claims 14-20, when said program code is executed on the electronic control unit (19) or other computer connected to the electronic control unit.