DE102017214481A1 - Water injection device for an internal combustion engine - Google Patents

Abstract

For a water injection device for an internal combustion engine (2) comprising at least one water tank (5) for storing water, at least one water injector (6) for injecting the water into the internal combustion engine (2), at least one conveying element (3) for conveying water out of the water Water tank (5) in the water injector (6), wherein the conveying element (3) at least one input (9) and at least one output (10), wherein the water tank (5) connected to the input (9) of the conveying element (3) is and the output (10) of the conveying element (3) with the water injector (6) is connected, it is proposed that between the water tank (5) and the conveying element (3) at least one check valve (40) and at least one pressure relief valve (50) wherein the check valve (40) is openable in a first direction (41) from the water tank (5) to the inlet (9) of the conveyor element (3) and wherein the pressure relief valve (50) is arranged in a second direction (51). from the entrance (9) of the conveying element (3) to the water tank (5) can be opened.

Description

State of the art

The present invention relates to a water injection device for an internal combustion engine and such an internal combustion engine.

Due to increasing demands on reduced carbon dioxide emissions, internal combustion engines are increasingly being optimized with regard to fuel consumption. However, known internal combustion engines can not be optimally operated in terms of consumption at operating points with high load, since the operation is limited by knock tendency and high exhaust gas temperatures. A possible measure to reduce the tendency to knock and to lower the exhaust gas temperatures is the injection of water. There are usually separate water injection systems available to allow the water injection. For example, from the DE 10 2015 208 476 A1 a water injection system for an internal combustion engine known.

In water injection systems for internal combustion engines, a water tank is normally provided, so that at any time water is available for injection into the intake manifold or the combustion chamber of the internal combustion engine. In addition, in such water injection systems water can be obtained with the aid of a water extraction system, for example, from the exhaust system of the internal combustion engine in the motor vehicle or from the environment of the motor vehicle and, for example, also supplied to the water tank. From the water tank, for example, water can be conveyed by means of a pump via a distributor device to injection valves, through which the water is then injected, for example, into a suction pipe or a combustion chamber of the internal combustion engine. For this purpose, as in fuel injection systems, the distributor device, for example in the form of a rail, can be provided for storing water and distributing it to a plurality of injectors, through which the water can then be injected.

A peculiarity of water injectors for water over fuel injectors is that the injectors are emptied in the water injection after stopping the engine in order to prevent possible damage to the injectors and / or the entire injection system by freezing in the injectors and thereby expanding water. This can be done for example by the pump, which sucks the water from the injectors.

For example, between the operating points where the water injection system is activated, the pump used to convey the water is shut off. This means that the water is in the water injectors and the lines of the water injection system. Due to the high temperatures of the parts of the internal combustion engine in the vicinity of the water injection system, the standing water can heat up and possibly evaporate. This effect is exacerbated when driving at high altitude, where the air pressure is lower. The formation of steam can lead to functional impairments when restarting the water injection system, since the system pressure can only be built up by the steam with a delay. Thus, the water injection system is delayed ready for operation. Due to this delayed operational readiness, temperature peaks in the exhaust gas as well as knocking events during combustion can occur during rapid load transients.

Disclosure of the invention

According to the invention, a water injection device for an internal combustion engine is proposed. The water injection device comprises at least one water tank for storing water, at least one water injector for injecting the water into the internal combustion engine, at least one conveying element for conveying water from the water tank into the water injector, wherein the conveying element comprises at least one inlet and at least one outlet.
The water tank is connected to the entrance of the conveying element and the outlet of the conveying element is connected to the water injector. According to the invention, at least one check valve and at least one pressure relief valve are arranged between the water tank and the conveying element, the check valve being openable in a first direction from the water tank to the inlet of the conveying element and the pressure relief valve being directed in a second direction from the inlet of the conveying element to the water tank is openable.

Advantages of the invention

Compared with the prior art, the water injection device for an internal combustion engine has the advantage that when conveying water from the water tank to the water injector, the water can be conveyed only in the first direction from the water tank to the water injector. In the other direction, ie from the water injector to the tank, the check valve closes, blocking the flow of water. When the area between the check valve and the water injectors is filled with water, a closed area between the check valve and the water injectors is formed by the closed check valve. So the system pressure in this area between check valve and water injectors can also be in inactive phases the water injection device are kept above the vapor pressure of the water. Thus, a vapor formation of the water is avoided and ensures short pressure build-up times and a fast injection release. The check valve is designed for a pressure which prevents vapor bubbles from forming in the area between the check valve and water injectors under given operating conditions.

At the same time in the water injection device according to the invention by the pressure relief valve in the water injectors, in the distributor device and / or in other components of the water injection device located water can be advantageous easily and quickly conveyed back through the pressure relief valve, for example in the water tank. Thus, for example, the water injectors can advantageously be quickly and easily freed of water, for example when the internal combustion engine is switched off. Thus, the water injectors, the distributor device and other components of the water injection device are advantageously protected against damage by freezing water in the injection valves. The pressure relief valve can be advantageously opened, for example by backward conveying the conveying element, and thus the area between the check valve and the water injectors are emptied of water, so that the water injectors and the lines are protected from damage by freezing and expanding water.

Further advantageous embodiments and modifications of the invention are made possible by the features specified in the subclaims.

According to an advantageous embodiment, it is provided that the check valve comprises at least one check valve housing, wherein on the check valve housing at least one check valve seat is formed, wherein a reaction with at least one check valve spring non-return valve body cooperates with a check valve seat and / or that the pressure relief valve comprises at least one pressure relief valve housing, wherein at least one pressure relief valve seat is formed on the overpressure valve housing, wherein a pressure relief valve body acted upon by at least one overpressure valve spring cooperates with a pressure relief valve seat.

According to an advantageous embodiment, it is provided that the check valve is formed in the pressure relief valve body of the pressure relief valve. The check valve is thus advantageously integrated into the pressure relief valve and the assembly of check valve and pressure relief valve can thus be designed advantageously compact.

According to an advantageous embodiment, it is provided that the pressure relief valve is formed in the check valve body of the check valve. The pressure relief valve is thus advantageously integrated into the check valve and the assembly of check valve and pressure relief valve can thus be designed advantageously compact.

According to an advantageous embodiment, it is provided that the pressure relief valve is designed such that it can be opened by a pressure prevailing at the inlet of the conveyor element and generated by the conveyor element pressure. The conveyor element can thus generate pressure and open the pressure relief valve, so that the area between the check valve and water injectors can be emptied of water.

According to an advantageous embodiment, it is provided that the pressure relief valve is designed such that it can be opened by a pressure prevailing at the inlet of the conveying element and generated by the conveying element by reversing the conveying direction of the conveying element. Thus, the overpressure valve can be opened, for example, by reversing the conveying direction of the conveying element, ie in backward conveying, by the pressure built up at the inlet of the conveying element by the conveying element and thus emptying the area between the non-return valve and the water injector of water.

Furthermore, according to the invention, a method for operating a water injection device of an internal combustion engine is proposed. The water injection device comprises at least one water tank for storing water, at least one water injector for injecting the water into the internal combustion engine, at least one conveying element for conveying water from the water tank into the water injector, wherein the conveying element comprises at least one inlet and at least one outlet, wherein the Water tank is connected to the input of the conveying element and the output of the conveying element is connected to the water injector, wherein between the water tank and the conveying element at least one check valve and at least one pressure relief valve are arranged, wherein the check valve in a first direction from the water tank to the input of Conveying element is openable and wherein the pressure relief valve in a second direction from the entrance of the conveying element to the water tank can be opened. The method comprises a step of conveying water from the water tank to the water injector by means of the conveyor element, wherein the check valve is opened during conveyance and water in the first direction flows through the check valve to the water injector and the pressure relief valve during conveyance closed is. Furthermore, the method comprises a step of returning water from the water injector to the water tank by means of the conveying element, wherein the check valve is closed during the return feeding and the relief valve is open during the return feeding, so that water flows in a second direction through the pressure relief valve to the water tank ,

According to an advantageous embodiment, the method further comprises a step for stopping the conveying element, wherein the check valve and the pressure relief valve are closed.

According to an advantageous embodiment, it is provided that when conveying water back from the water injector to the water tank by means of the conveying element, the conveying element at the entrance of the conveying element provides a pressure, so that the pressure relief valve is opened by the pressure.

list of figures

• 1 eine schematische Ansicht einer Brennkraftmaschine mit einer Wassereinspritzvorrichtung gemäß eines ersten Ausführungsbeispiels der vorliegenden Erfindung,
• 2 eine schematische Ansicht eines Förderelementes mit einem Rückschlagventil und einem Überdruckventil,
• 3. eine schematische Darstellung eines Ausführungsbeispiels eines Rückschlagventils und eines Überdruckventils,
• 4 eine schematische Ansicht einer Brennkraftmaschine mit einer Wassereinspritzvorrichtung gemäß eines zweiten Ausführungsbeispiels der vorliegenden Erfindung,
• 5 eine schematische Ansicht einer Brennkraftmaschine mit einer Wassereinspritzvorrichtung gemäß eines dritten Ausführungsbeispiels der vorliegenden Erfindung.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it

• 1 1 is a schematic view of an internal combustion engine having a water injection device according to a first embodiment of the present invention;
• 2 a schematic view of a conveying element with a check valve and a pressure relief valve,
• 3 , a schematic representation of an embodiment of a check valve and a pressure relief valve,
• 4 1 is a schematic view of an internal combustion engine having a water injection device according to a second embodiment of the present invention;
• 5 a schematic view of an internal combustion engine with a water injection device according to a third embodiment of the present invention.

Embodiments of the invention

Hereinafter, with reference to the figures, a water injection device 1 an internal combustion engine 2 described in detail according to various embodiments. In particular, the internal combustion engine 2 operated according to the Otto principle and with gasoline direct injection.

In 1 are the internal combustion engine 2 as well as the water injection device 1 shown schematically. The internal combustion engine 2 has a plurality of cylinders. The internal combustion engine 2 includes one cylinder per cylinder 20 in which a piston 21 is movable back and forth. Furthermore, the internal combustion engine 2 For example, one inlet channel per cylinder 22 on, over which air to the combustion chamber 20 is supplied. Exhaust gas is via an exhaust duct 23 dissipated. These are at the inlet channel 22 an inlet valve 25 and at the exhaust duct 23 an outlet valve 26 arranged. The reference number 24 further denotes a fuel injection valve.

The water injection device 1 is an injection device through the water in the engine 2 is injected. In addition to the water, other media can be mixed with the water and stored, conveyed and injected together with the water. Thus, for example, alkanols, such as, for example, ethanol or methanol or other additives which prevent, for example, freezing of the water, may be admixed with the water.

The water injection device 1 includes at least one water injector 6 , The water injector 6 is at the inlet channel 22 arranged. The water injector 6 injects water into the inlet channel 22 the internal combustion engine 2 one. The water injector 6 is for example by a control unit 13 driven. In this embodiment, a water injector 6 per cylinder provided. Alternatively, two water injectors per cylinder can be arranged for better treatment or to increase the maximum amount of water injectable per combustion cycle. But it can also, for example, only a water injector 6 be provided for all cylinders.

Furthermore, the water injection device comprises 1 an example designed as a pump conveyor element 3 and an electric drive 4 for driving the conveyor element 3 , The electric drive 4 for example, via the control unit 13 driven. The conveying element 3 can water from the water tank 5 to the water injectors 6 promote. The conveying element 3 but it can also take water from the water injector 6 to the water tank 5 back support. The change between conveying water tank 5 to the water injectors 6 for returning the water injectors to the water tank 5 For example, by changing the operating direction of the conveyor element 3 , So for example, a change in the direction of rotation of the pump happen.

On the conveyor element 3 is an entrance 9 an exit 10 educated. The entrance 9 of the conveyor element 3 is the area through which water in the extraction of water from the water tank 5 to the injectors 6 in the conveying element 3 flows. The exit 10 of the conveyor element 3 is the area through which water is pumping the water from the water tank 5 to the water injectors 6 from the conveyor element 3 flows. Furthermore, the water injection device comprises 1 a water tank 5 for storing water. The water tank 5 is fluidic with the entrance 9 of the conveying element 3 connected. The water tank 5 For example, by a first line 7 with the entrance 9 of the conveyor element 3 connected. The conveying element 3 but can also be configured for example as a submersible pump and in the water tank 5 be arranged so that the water from the water tank 5 directly over the entrance 9 of the subsidy 3 the conveying element 3 can be supplied and the input 9 of the conveyor element 3 in this way with the water tank 5 is fluidically connected. The exit 10 of the conveyor element 3 is with the at least one water injector 6 fluidly connected. The exit 10 of the conveyor element 3 can, for example, by a second line 8th with the water injectors 6 , The water injectors 6 For example, they can be connected to a distributor, for example a rail, and via the second line 8th and the distributor, not shown in the figures, with the output 10 of the conveyor element 3 be connected.

As in 1 and 2 illustrated, includes the water injection device 1 continue a check valve 40 , The check valve 40 is in a first direction 41 from the water tank 5 to the entrance 9 of the conveyor element 3 openable. When pumping the water from the water tank 5 to the water injector 6 opens the check valve 40 and lets water in the first direction 41 through the check valve 40 flow. In the opposite direction blocked the check valve 40 and lets water from the water injectors 6 not through the check valve 40 to the water tank 5 flow back.

The check valve 40 is set up, de-energized by a pressure of the water at the check valve 40 , which, for example, a force of a check valve spring 43 acts to be opened (open position of the check valve 40 ). When the pressure on the check valve 40 the force of the check valve spring 43 can not overcome, closes the check valve 40 (closed position). In the figures, there is the check valve 40 in the closed position.

The check valve 40 is between the water tank 5 and the conveyor element 3 arranged. The check valve 40 So, for example, at the end of the first line 7 and at the entrance 9 of the conveyor element 3 be arranged. But it can also be in the first line, for example 7 be arranged.

In this embodiment, the check valve comprises 40 at least one check valve housing 42 , At the check valve body 42 is a check valve seat 45 educated. Furthermore, the check valve includes 40 a check valve body 44 , The check valve body 44 is from a check valve spring 43 acted upon, so he with the check valve seat 45 interacts. The check valve 40 is at rest of the check valve body 44 on the check valve seat 45 closed. The check valve body 44 is dependent on an inlet opening 46 the check valve 40 and at an outlet opening 47 the check valve 40 prevailing pressures of the water pressure difference dependent from the check valve seat 45 deflected, leaving water pressure-difference-dependent in the first direction 41 from the inlet opening 46 the check valve 40 to the outlet opening 47 the check valve 40 flows.

The check valve 40 but can also be in accordance with other embodiments, not shown in the figures, be gestalltet. So can the check valve 40 also without check valve spring 43 be educated. The check valve 40 For example, it may be a diaphragm valve in which the opening and closing of the port is through a diaphragm. Furthermore, the check valve 40 Also include a piece of tubing through which the opening of the check valve 40 is released or closed.

Furthermore, the water injection device comprises 1 a pressure relief valve 50 , The pressure relief valve 50 is in a second direction 51 from the entrance 9 the conveying element to the water tank 5 openable. The pressure relief valve 50 So for example, against the check valve 40 concerning the entrance 9 of the conveyor element 3 and the water tank 5 openable in the opposite direction. Exceeds the pressure at the entrance 9 of the conveyor element 3 a limit, so the pressure relief valve 50 open and water may be out of the area between the check valve 40 and the water injectors 6 back to the water tank 5 flow.

The pressure relief valve 50 is set up a pressure between the pressure relief valve 50 and the water injector 6 to maintain a level at which evaporation of the between the pressure relief valve 50 and the water injector 6 water is prevented. Preferably, the pressure relief valve 50 set up the system pressure in the area between the pressure relief valve 50 and the water injectors 6 to keep at a level greater than two bar. The pressure relief valve 50 is from one to the pressure relief valve 50 applied pressure greater than an opening pressure of the pressure relief valve 50 open. The opening pressure is less than one Pressure, the moist, not filled with water conveyor element 3 in the return direction to the pressure relief valve 50 can generate. The pressure relief valve 50 is thus set up so that the conveying element 3 can overcome the opening pressure, even in non-water-filled state, and the pressure relief valve 50 thus remains open when recirculating the water.

Because of the pressure relief valve 50 when closed, the system pressure in the area between the pressure relief valve 50 and the water injectors 6 Keeping at the level is the water injector 1 operational at inactive operating points and can be put into use quickly when the combustion of the internal combustion engine 2 to request a water injection.

In the opposite direction from the water tank 5 to the entrance 9 of the conveyor element 3 blocks the pressure relief valve 50 the water flow. Thus, by the pressure relief valve 50 no water from the water tank 5 to the entrance 9 of the conveyor element 3 flow. The pressure relief valve 50 is between the water tank 5 and the conveyor element 3 arranged. The pressure relief valve 50 So, for example, at the end of the first line 7 and at the entrance 9 of the conveyor element 3 be arranged. But it can also be in the first line, for example 7 be arranged. The pressure relief valve 50 is set up water in the first direction 41 from the water tank 5 to the conveyor element 3 to block and water in the second direction 51 from the conveyor element 3 to the water tank 5 to flow at a pressure higher than a minimum pressure.

In this embodiment, the pressure relief valve comprises 50 a pressure relief valve housing 52 , At the pressure relief valve housing 52 is a pressure relief valve seat 55 educated. Furthermore, the pressure relief valve includes 50 a pressure relief valve body 54 , The pressure relief valve body 54 comes with a relief valve spring 53 charged and against the pressure relief valve seat 55 pressed. The pressure relief valve body 54 is dependent on an inlet opening 56 the pressure relief valve 50 and at an outlet opening 57 the pressure relief valve 50 prevailing pressures of the water pressure difference-dependent from the pressure relief valve seat 55 deflected, leaving water pressure-difference-dependent in the second direction 51 from the inlet opening 56 the pressure relief valve 50 to the outlet opening 57 the pressure relief valve 50 can flow. The pressure relief valve body 54 is through one at the entrance 9 of the conveyor element 3 prevailing pressure from the pressure relief valve seat 55 deflectable. The pressure relief valve 50 is thus by one at the entrance 9 of the conveyor element 3 prevailing pressure openable. The pressure to open the pressure relief valve 50 is necessary, for example, by the conveyor element 3 be generated. To generate this pressure, the conveying element 3 for example, in the reverse direction, ie by reversing the conveying direction of the conveying element 3 to be operated so that the conveying element 3 Water from the exit 10 of the conveyor element 3 to the entrance 9 of the conveyor element 3 promotes and thus at the entrance 9 of the conveyor element 3 builds up a pressure that is high enough around the pressure relief valve 50 to open and water from the water injector 6 to the water tank 5 zurückzufördern.

As in the in the 1 and 2 illustrated first embodiment of the water injection device 1 is shown, is the outlet opening 47 the check valve 40 fluidic with the entrance 9 of the conveyor element 3 connected. The inlet opening 46 the check valve 40 is fluid with the water tank 5 connected. At the same time is the inlet opening 56 the pressure relief valve 50 fluidic with the entrance 9 of the conveyor element 3 connected and the outlet opening 57 the pressure relief valve 50 fluidly with the water tank 5 connected. In the first embodiment, as in FIG 1 and 2 shown, the check valve 40 and the pressure relief valve 50 arranged fluidically parallel to each other.

The check valve 40 and the pressure relief valve 50 But, as in the embodiments in the 3 to 5 shown, also integrated into each other.

In 3 is an embodiment of a check valve 40 that is in a pressure relief valve 50 integrated, shown. The pressure relief valve 50 includes a pressure relief valve housing 52 , At the pressure relief valve housing 52 is a pressure relief valve seat 55 educated. Furthermore, the pressure relief valve includes 50 a pressure relief valve body 54 , The pressure relief valve body 54 comes with a relief valve spring 53 charged and against the pressure relief valve seat 55 pressed. The pressure relief valve 50 is in 3 closed, the pressure relief valve body 54 at the pressure relief valve seat 55 is applied. The check valve 40 is in the pressure relief valve body 54 educated. In this embodiment, the pressure relief valve body is used 54 as a check valve housing 42 the check valve 40 , In the pressure relief valve body 54 For this purpose, a through opening is formed, which extends from the check valve body 44 is closed. The check valve body 44 lies on a check valve seat 45 on. The check valve seat 45 is at the pressure relief valve body 54 educated. The check valve body 44 is by a check valve spring 43 on the check valve seat 45 pressed and thus closes the opening in the pressure relief valve body 54 , The check valve spring 43 relies on the pressure relief valve body 54 from. The check valve 40 is in the opposite direction as the pressure relief valve 50 in which it is integrated, openable.

In 4 is the check valve 40 that is in a pressure relief valve 50 integrated in the water injector 1 shown. It is in the pressure relief valve 50 integrated check valve 40 in this embodiment in the first line 7 arranged. Water can from the water tank 5 through the open check valve 40 to the entrance of the conveyor element 3 flow, while the pressure relief valve 50 closed is. Water can in the opposite direction of flow from the entrance 9 of the conveyor element 3 through the opened pressure relief valve 50 in water tank 5 be promoted, at the same time the check valve 40 closed is.

5 is a pressure relief valve 50 shown in a check valve 40 is integrated. Here is the pressure relief valve 50 in the check valve body 44 educated. This is in the check valve body 44 a through opening provided and on the check valve body 44 a pressure relief valve seat 55 educated. The pressure relief valve body 54 is by a pressure relief spring 53 acted upon and thus against the pressure relief valve body 55 pressed so that the opening in the check valve body 44 through the support of the pressure relief valve body 54 at the pressure relief valve seat 55 is closed. The pressure relief spring 53 relies on the check valve body 44 from. It is in the check valve 40 integrated pressure relief valve 50 for example, in the first line 7 arranged. Water can from the water tank 5 through the open check valve 40 to the entrance of the conveyor element 3 flow, while the pressure relief valve 50 closed is. Water can in the opposite direction of flow from the entrance 9 of the conveyor element 3 through the opened pressure relief valve 50 in water tank 5 be promoted, at the same time the check valve 40 closed is.

Of course, other embodiments and hybrid forms of the illustrated embodiments are possible.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102015208476 A1 [0002]

Claims (9)

Water injection device for an internal combustion engine (2) comprising at least one water tank (5) for storing water, at least one water injector (6) for injecting the water into the internal combustion engine (2), at least one conveying element (3) for conveying water from the water tank (3). 5) in the water injector (6), wherein the conveying element (3) at least one input (9) and at least one output (10), wherein the water tank (5) with the input (9) of the conveying element (3) is connected and the outlet (10) of the conveying element (3) is connected to the water injector (6), characterized in that between the water tank (5) and the conveying element (3) at least one check valve (40) and at least one pressure relief valve (50) are arranged wherein the check valve (40) is openable in a first direction (41) from the water tank (5) to the inlet (9) of the conveyor element (3), and wherein the pressure relief valve (50) is open in a second direction (51) from the E ingang (9) of the conveying element (3) to the water tank (5) is openable. Water injector after Claim 1 characterized in that the check valve (40) comprises at least one check valve housing (42), wherein on the check valve housing (42) at least one check valve seat (45) is formed, with a at least one check valve spring (43) acted upon check valve body (44) with a Non-return valve seat (45) cooperates and / or that the pressure relief valve (50) comprises at least one pressure relief valve housing (52), wherein at the overpressure valve housing (52) at least one pressure relief valve seat (55) is formed, wherein an at least one pressure relief spring (53) acted upon overpressure valve body ( 54) cooperates with a pressure relief valve seat (55). Water injector after Claim 2 , characterized in that the check valve (40) in the pressure relief valve body (54) of the pressure relief valve (50) is formed. Water injector after Claim 2 , characterized in that the pressure relief valve (50) in the check valve body (44) of the check valve (40) is formed. Water injection device according to one of the preceding claims, characterized in that the pressure relief valve (50) is designed such that it can be opened by a pressure prevailing at the inlet (9) of the conveyor element (3) and generated by the conveyor element (3). Water injection device according to one of the preceding claims, characterized in that the pressure relief valve (50) is designed such that it by a at the input (9) of the conveying element (3) prevailing and by the conveying element (3) by reversing a conveying direction of the conveying element (3). generated pressure can be opened. Method for operating a water injection device (1) for an internal combustion engine (2) comprising at least one water tank (5) for storing water, at least one water injector (6) for injecting the water into the internal combustion engine (2), at least one conveying element (3) for Conveying water from the water tank (5) into the water injector (6), the conveying element (3) comprising at least one inlet (9) and at least one outlet (10), the water tank (5) communicating with the inlet (9) of the water tank (5) Conveying element (3) is connected and the output (10) of the conveying element (3) with the water injector (6) is connected, between the water tank (5) and the conveying element (3) at least one check valve (40) and at least one pressure relief valve ( 50) are arranged, wherein the check valve (40) in a first direction (41) of the water tank (5) to the input (9) of the conveying element (3) is openable and wherein the pressure relief valve (50) in a second direction (51) is openable from the inlet (9) of the conveyor element (3) to the water tank (5), the steps of the method comprising: Conveying water from the water tank (5) to the water injector (6) by means of the delivery element (3), the check valve (40) being open during delivery and water in the first direction (41) passing through the check valve (40) Water injector (6) flows and the pressure relief valve (50) is closed during conveying, - Returning water from the water injector (6) to the water tank (5) by means of the conveying element (3), wherein the check valve (40) is closed during the return feed and the pressure relief valve (50) is opened during the return feed, so that water in one second direction (51) through the pressure relief valve (50) to the water tank (5) flows. Method according to Claim 7 , characterized in that the steps of the method further comprise: - stopping the conveying element (3), wherein the check valve (40) and the pressure relief valve (50) are closed. Method according to one of Claims 7 or 8th , characterized in that when conveying back water from the water injector (6) to the water tank (5) by means of the conveying element (3) the conveying element (3) at the entrance of the conveying element (3) provides a pressure so that the pressure relief valve (50) is opened by the pressure.

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