jet pump

Abstract

Jet pump (2) for supplying hydrogen in a fuel cell system, comprising a nozzle assembly (10) and a needle (30) adjustable to change an outlet cross-section in a bearing bore (13) of the nozzle assembly (10), wherein the nozzle assembly (10) has a nozzle carrier (12) and a bearing (11) of the needle (30) comprising the bearing bore (13), wherein the nozzle assembly (10) has at least one recess (24) extending along the needle (30) on the bearing bore (13), wherein the recess (24) is designed as an axial groove on the bearing bore (13).

Description

[0001] The invention relates to a jet pump for supplying hydrogen to a fuel cell system, comprising a nozzle assembly and a needle adjustable to change the outlet cross-section, wherein the nozzle assembly has a nozzle carrier and a bearing for the needle comprising the bearing bore. The invention further relates to a bearing for the needle of a jet pump.

[0002] The jet pump is particularly suitable for use in applications where adjustable jet pump output is required. For example, the jet pump can be used in hydrogen-powered vehicles.

[0003] DE 10 2021 108 601 A1 describes a hydrogen injection device for a fuel cell with passive recirculation, comprising a hydrogen supply, a recirculation gas supply, a jet pump with nozzle and nozzle needle for the hydrogen, a mixing unit, and a linear actuator for moving a valve piston with the nozzle needle. Pressure compensation of the valve piston can be achieved via a bypass bore in the housing and / or actuator or via a longitudinal groove in the armature and / or the nozzle needle.

[0004] DE 10 2021 130 875 A1 describes a jet pump for a fuel cell system with hydrogen recirculation, comprising a nozzle section for guiding and mixing hydrogen and an actuator for adjusting a nozzle needle. At least one fluid channel extends from the nozzle section to the actuator. The fluid channel runs parallel to the nozzle needle and thus to the central axis of the jet pump and is designed as an overflow channel. Furthermore, an annular space directly surrounding the nozzle needle is present.

[0005] DE 10 2023 110 057 A1 discloses a jet pump with a nozzle upstream of a mixing tube, in which a nozzle needle is displaceable. An actuator is provided for adjusting the nozzle needle, which comprises an armature rigidly connected to the nozzle needle. The nozzle needle and / or the armature may be provided with a carbon-containing coating.

[0006] DE 10 2013 014 978 A1 describes an anode circuit for a fuel cell with a water separator and a gas jet pump as a recirculation pumping device. In this circuit, one suction side of the gas jet pump is directly connected to the volume of the water separator.

[0007] Conventional jet pumps are technically complex to manufacture. This is primarily due to the high precision and accuracy required of the nozzle assembly in its interaction with the needle, in order to adjust the outlet cross-section precisely and reliably over the long term. The associated manufacturing effort results in high costs.

[0008] The invention aims to provide a jet pump and a needle bearing that are cost-effective to manufacture yet offer high precision and accurate fluid delivery, thereby ensuring reliable long-term operation. In particular, the disadvantages of the prior art are to be avoided or at least reduced.

[0009] The problem is solved by the features of the independent claims. Preferred embodiments are specified in the dependent claims and in the description, each of which, individually or in combination, can represent an aspect of the invention.

[0010] A jet pump for supplying hydrogen to a fuel cell system is proposed, comprising a nozzle assembly and a needle that is adjustable in a bearing bore of the nozzle assembly or relative to the nozzle assembly for changing an outlet cross-section, wherein the nozzle assembly has a nozzle carrier and a bearing for the needle comprising the bearing bore. The nozzle assembly has at least one recess extending along the needle on the bearing bore, wherein the recess is designed as an axial groove on the bearing bore.

[0011] The jet pump is specifically designed for use in a fuel cell system with hydrogen recirculation, or for recirculating hydrogen in a fuel cell system, particularly in a vehicle. For example, the fuel cell system is operated by passing recirculated hydrogen, which has passed through fuel cells, through the jet pump. The jet pump, or its outlet cross-section, is adjusted to adapt the total hydrogen supply from fresh and recirculated hydrogen. The jet pump preferably has a mixing chamber arranged downstream of the nozzle assembly. The jet pump is preferably configured to supply the hydrogen to the mixing chamber via the nozzle assembly.

[0012] The jet pump designed for supplying or recirculating hydrogen in a fuel cell system preferably comprises, in a basic design known per se, means for varying the mixing ratio between fresh, high-pressure hydrogen and recirculating hydrogen. These means include, for example, an actuator and the needle or nozzle needle, which can be actuated by the actuator and is preferably linearly displaceable, and which is preferably displaceable within a housing or pump housing of the jet pump. Preferably, the needle or nozzle needle is adjustable within the nozzle assembly over at least a certain adjustment range, with the nozzle assembly itself also being arranged or held in and / or forming the housing or pump housing. A primary connection or supply is preferably provided for feeding the fresh hydrogen into the housing or pump housing.A secondary connection of the jet pump or a suction side is preferably provided for the supply of recirculating hydrogen.

[0013] In other words, for example, an adjustable pump for a fluid, particularly hydrogen, is proposed, comprising a nozzle assembly with a needle arranged and / or guided therein. The needle is adjustable within and / or guided to the nozzle assembly. The nozzle assembly contains at least one recess designed as an axial groove, extending along the needle or substantially parallel to the needle in the area between the needle and the nozzle assembly, which can be traversed by hydrogen and which serves to support the needle. The recess is directly adjacent to the needle. A mixing chamber is preferably provided downstream of the nozzle assembly and the needle.

[0014] In a preferred embodiment of the jet pump, at least one additional bore is arranged besides the bearing bore.

[0015] In a simplified sense, the term hydrogen is also used for hydrogen-containing gas mixtures or gas-liquid mixtures flowing within a fuel cell system. The hydrogen gas flowing through the supply channel or feeder is also referred to as fresh hydrogen. The pressure of the fresh hydrogen is significantly higher than the pressure of the recirculated hydrogen drawn from an anode side of the fuel cell system.

[0016] In particular, the outlet cross-section of the outlet opening is adjustable by adjusting the needle. The needle can be adjusted along its length. Specifically, the needle can be adjusted axially, preferably only axially. For example, by immersing or axially penetrating the needle into the nozzle assembly, the outlet cross-section, which is preferably formed by an annular gap between the needle and the nozzle assembly, is reduced, and / or by withdrawing the needle from the nozzle assembly, the outlet cross-section is increased. This can be achieved, for example, by the needle having a tip that tapers along the flow direction and / or being pointed. In other words, for example, the needle tapers to a point at its free end, preferably by means of a conically tapered end section.

[0017] The needle is, for example, slidably mounted in the bearing bore and / or in the needle bearing assembly. The needle bearing assembly can also be referred to as a needle bearing or needle bearing body. The needle bearing assembly is not a rolling bearing. The bearing bore or needle bearing assembly is primarily designed to guide the needle, specifically to guide it as linearly as possible and without rotation. The bearing bore is typically integrated into the nozzle assembly, particularly in a component inserted into a nozzle holder, such as a needle bearing, and / or in the nozzle holder itself. The bearing bore can generally have a cylindrical or round cross-section, with at least one recess giving it a different appearance.The recess, running along the length of the needle, is regularly at least substantially as long as the bearing bore itself, thus preferably extending from side to side of the part containing the bearing bore, particularly the needle bearing. The needle bearing is made of metal (e.g., steel) and / or plastic (e.g., PTFE).

[0018] The statement that the recess is located "at the bearing bore" means that the recess is directly adjacent to the bearing bore. The recess can therefore be part of the bearing bore itself. In this case, the recess can be understood as a radial recess of the bearing bore.

[0019] Additional bores, on the other hand, are arranged next to and spaced apart from the bearing bore, particularly in a direction transverse or orthogonal to the needle's extent. The bearing bore can run parallel to the needle.

[0020] In one embodiment of the jet pump, at least one recess can run at an angle to the bearing bore. For example, the recess can open laterally into the bearing bore or extend radially from the bearing bore.

[0021] The jet pump can include an actuator, in particular a needle actuator. The actuator can be designed to actuate the needle, especially in the extension or axial direction. The actuator can be fixed to the nozzle assembly. The actuator can be controlled electrically, pneumatically, or hydraulically, for example, by means of compressed air or by means of the fluid or hydrogen. The actuator preferably includes an electric stepper motor or an electric solenoid to adjust the needle.

[0022] The term nozzle assembly refers in particular to a component that provides the outlet cross-section for the fluid or hydrogen. The nozzle assembly can also be understood as a nozzle carrier assembly. The outlet cross-section can be influenced or adjusted in conjunction with the needle. The outlet cross-section is preferably a cross-sectional constriction to influence the flow of the fluid or hydrogen as it exits the nozzle assembly. The nozzle assembly preferably has a nozzle guide that is at least substantially cylindrical, particularly opposite the needle bearing or the bearing bore, viewed along the length of the needle.

[0023] The nozzle assembly comprises, in particular, a substantially enclosed space or feed chamber to which the outlet cross-section is fluidically connected. The supply for fresh hydrogen preferably opens into the enclosed space upstream of the outlet cross-section. The needle is also preferably arranged in the enclosed space. The outlet cross-section is preferably a constriction to influence the flow of hydrogen as it passes from the enclosed space out of the nozzle assembly, for example, towards a mixing tube or diffuser, where recirculated hydrogen can optionally also be drawn in. The adjustable needle preferably acts within the outlet cross-section to modify the flow conditions by changing the shape and / or size of the outlet cross-section.In particular, the nozzle assembly, in conjunction with the needle, performs no work and converts between the velocity and static pressure of the hydrogen. Preferably, the velocity of the hydrogen is increased while its static pressure is reduced.

[0024] The term "needle" refers in particular to a component of elongated shape. The needle is specifically designed to be inserted into the nozzle assembly. The needle can, in particular, be inserted into a nozzle element or nozzle. The needle is designed, in particular, at its end or tip, to correspond to the nozzle assembly or nozzle element, especially such that a precise insertion of the nozzle assembly into the nozzle element is possible. The maximum diameter of the needle at the tip or in the tip region can essentially correspond to the inner diameter of the nozzle assembly, for example, be between 0 and 10% smaller, preferably between 0 and 5% smaller. The needle can have a cylindrical section, a conical section, and / or a conical tip section or tip.In particular, the cylindrical section and the preferably conical tip located downstream of the cylindrical section are designed to be immersed in the nozzle assembly in order to adjust the outlet cross-section, which is particularly designed as an annular gap formed between the needle and the nozzle assembly or the nozzle element, in conjunction with the nozzle assembly or the nozzle element. Thus, when the needle is adjusted in the nozzle assembly, a circumferential (annular) gap is reduced or enlarged.

[0025] The at least one recess is arranged opposite the exit cross-section. The needle is preferably connected to an actuator, for example a solenoid, which can adjust the needle. The actuator can move the needle through the bearing bore and, in particular, adjust the exit cross-section.

[0026] In particular, the needle is linearly movable and projects into the nozzle assembly or the outlet cross-section. Two end positions, for example "fully open" and "fully closed", and preferably intermediate positions, can be easily set by linear movement of the needle.

[0027] The term "recess" refers in particular to a material retraction or removal. The recess can be configured as a bore, sink, slot, engraving, or other indentation. The recess preferably extends at least substantially in the axial direction and / or along the needle, particularly parallel to it, i.e., on the side of the nozzle assembly facing the needle. The recess is preferably continuous and / or uninterrupted in the axial direction and / or within the nozzle assembly or nozzle carrier, especially the needle bearing. The recess necessarily also has a radial extension or an extension transverse to the needle, which, however, is typically significantly smaller than its axial extension or its extension along the needle. The recess advantageously serves to provide a venting bore and / or a reduction in shear area on the needle.This can ensure that condensate in the nozzle assembly is effectively drained and that icing is less likely. Pressure equalization is possible regardless of the needle's position. Liquid water may drain from the (still warm) nozzle assembly when the jet pump or vehicle is switched off. Furthermore, pressure equalization can occur at the needle bearing or bearing bore during operation, reducing friction.

[0028] The invention recognizes that a conventional jet pump – even without a recess – can become clogged, freeze, or jammed, and places high demands on its manufacture. The invention, thanks in particular to at least one additional bore arranged next to the bearing bore, allows for greater manufacturing precision without significant drawbacks, thus reducing costs. At the same time, an effective jet pump is provided that, surprisingly, also handles condensation better.

[0029] In particular, the recess located in the bearing bore reduces the shear and / or contact surface that forms between the needle and the nozzle assembly during operation. In practice, the precise fit between the needle and nozzle assembly has resulted in increased friction and ultimately increased wear in the shear and contact surface. The recess advantageously reduces the shear and contact surface, thereby reducing friction and ultimately wear in the area of ​​the directly adjacent surfaces between the needle and nozzle assembly. This provides an optimized and more durable bearing arrangement.

[0030] The invention addresses the challenge of sealing during the guidance and pumping of hydrogen, which is extremely difficult due to the size of hydrogen molecules. The proposed solution significantly improves and simplifies the sealing process. In particular, the invention, with its recessed design, offers the advantage of eliminating the need for separate sealing technology or seals at the shear and / or contact surface of the nozzle assembly or at other points on the jet pump.

[0031] According to the invention, the recess is designed as an axial groove in the bearing bore. The groove can extend substantially axially or exclusively axially. For example, the groove can run parallel to the axial direction or to the needle, or at an angle or inclination to it. The groove can be spiral, straight, or angled once or multiple times. The groove thus also extends radially, but only to a subordinate extent compared to the axial direction, for example, by a smaller amount and / or by an order of magnitude. In this way, effective adjustment of the jet pump can be achieved while maintaining its cost-effective manufacturing and the advantages with regard to condensate.

[0032] Several of these depressions can be provided, for example, two, three, or four. The multiple depressions can be arranged around the needle or distributed circumferentially to achieve a uniform flow. Multiple depressions result in a more homogeneous flow and also more reliable drainage and / or reduction of shear area. For example, the multiple depressions can be arranged at least substantially uniform intervals circumferentially.

[0033] The nozzle assembly can include a nozzle element arranged coaxially to the needle on or within the nozzle carrier and / or surrounding the needle. The nozzle element preferably serves to form the outlet cross-section in conjunction with the needle. The nozzle element can provide the actual functional nozzle. The nozzle element can be designed to guide and / or contact the needle. The outlet cross-section can be formed between the nozzle assembly, in particular the nozzle element, and the needle. The nozzle carrier can have a hydrogen supply or connection and / or a mounting point or receptacle for an actuator for the needle or a needle actuator. Furthermore, the nozzle carrier can be designed for mounting on a mixing tube.

[0034] An actuator may be provided. The actuator is intended for actuating the needle. The actuator may be arranged adjacent to the needle bearing. The actuator is preferably fixed to the nozzle assembly. The actuator can move the needle through the needle bearing or relative to the needle bearing and / or the nozzle assembly in order to change the outlet cross-section. The actuator may be arranged to be at least partially sealed from the environment of the jet pump or come into contact with hydrogen. In this respect, the recess can create pressure equalization within the jet pump.

[0035] The nozzle assembly, the needle bearing, the nozzle element, and / or the needle may have a coating. The coating may be designed to be wear-resistant and / or friction-reducing. The coating may be intended to contact the needle or the nozzle element. For example, a coating made of or containing carbon may be used. This allows the jet pump to be designed for exceptional durability.

[0036] The nozzle assembly, in particular the nozzle carrier and / or the nozzle element, can taper downstream or along the needle. The nozzle assembly can be conical, at least partially and / or along the needle. In particular, the nozzle carrier and / or the nozzle element is conical on the side facing the needle and / or away from a mixing chamber, or has a conical section, especially on the inside or concave. It is particularly preferred that the nozzle element is substantially cylindrical, at least partially, or has a cylindrical nozzle section or nozzle guide.

[0037] A mixing tube with a mixing chamber can be provided, in particular wherein the mixing chamber has a cylindrical section downstream of the nozzle assembly or nozzle element and / or, in particular adjacent to the cylindrical section, a section that widens conically downstream. The section that widens conically downstream can be designed as a diffuser.

[0038] Another solution involves a jet pump, for example, for supplying, and in particular recirculating, hydrogen in a fuel cell system. This jet pump comprises a nozzle assembly and a needle that is adjustable relative to the nozzle assembly to change the jet pump's outlet cross-section. The jet pump is described as follows, and the nozzle assembly includes a non-metallic nozzle carrier with a metallic, in particular annular, nozzle element. It is proposed that the nozzle element in the nozzle assembly be provided as a metallic, wear-resistant component, and the nozzle carrier as a non-metallic component (e.g., made of plastic) with simplified manufacturing. The nozzle element can also, in principle, be designed as a ceramic, wear-resistant (precision) component.

[0039] The nozzle holder and / or the needle bearing can be a standard component for all applications. The needle bearing and / or the bearing bore can be integrated into the nozzle holder. Preferably, the nozzle holder has one or more connections for the needle actuator, for operating gases (supply or hydrogen supply, suction side), mounting sections for connecting a stack module, and / or for at least one pressure and / or temperature sensor.

[0040] A hydrogen-powered vehicle is further proposed, equipped with the jet pump described herein. The vehicle has a horizontal plane that, when the vehicle is on a horizontal surface, is perpendicular to gravity. The jet pump's recess(s) are inclined to the horizontal plane, in particular by at least 2°, 5°, or 10°. The needle can be similarly oriented. Specifically, the needle points downwards or upwards, i.e., it is not parallel to the horizontal plane but inclined, transverse, or even perpendicular to it. For example, the recesses and their orientation and / or the needle are adapted to the installation situation of the jet pump or the needle and / or the actuator, so that liquid water can still flow out of the (warm) jet pump or its actuator during the shutdown phase.When installed horizontally, the ventilation holes are intentionally angled slightly to remove water from the actuator guide and prevent the actuator from freezing in sub-zero temperatures. In particular, the needle points towards the surface or downwards.

[0041] The invention is explained below by way of example with reference to the accompanying drawings and preferred embodiments, wherein the features shown below can represent an aspect of the invention, either individually or in combination. The drawings show: Fig. 1 a jet pump in a longitudinal section, Fig. 2A-B a jet pump with partially hidden parts in a longitudinal section (A) and in a perspective view only one bearing of the jet pump needle (B), and Fig. 3A-B a jet pump with partially hidden parts in a longitudinal section (A) and in perspective view only one bearing of the jet pump needle (B).

[0042] If the same reference symbols are used in the figures, the following description applies accordingly to the figures among themselves.

[0043] Fig. Figure 1 shows a jet pump 2 for supplying or recirculating hydrogen in a fuel cell system, in particular in a polymer electrolyte fuel cell system (PEM fuel cell system), or for other applications where adjustable jet pump performance is required.

[0044] The jet pump 2 comprises, as a nozzle carrier assembly, a nozzle assembly 10, a needle 30 which is adjustable along an axial direction by means of an actuator 4 (e.g., a solenoid) for changing an outlet cross-section relative to the nozzle assembly 10 in a bearing bore 13 of a bearing 11 of the needle 30 of the nozzle assembly 10, and a mixing chamber 42 arranged downstream of the nozzle assembly 10. The jet pump 2 is designed to supply a fluid, in particular hydrogen, to the mixing chamber 42 via the nozzle assembly 10.

[0045] The nozzle assembly 10 comprises a nozzle carrier 12, in particular made of plastic, which supports or has the bearing 11 of the needle 30. The bearing 11 of the needle 30 is essentially designed as a disc. The bearing 11 of the needle 30 is made of metal.

[0046] The bearing 11 of the needle 30 can also be incorporated into the nozzle carrier 12 and / or be formed materially bonded to the nozzle carrier 12.

[0047] The nozzle assembly 10 also includes, though this is generally optional, a nozzle element 20 arranged coaxially to the needle 30 in the nozzle carrier 12 and surrounding the needle 30 or the tip 32 of the needle 30, in particular a metallic one. The adjustable outlet cross-section is formed between the needle 30 and the nozzle assembly 10, more precisely the nozzle element 20. When the needle 30 is immersed further into the nozzle assembly 10 or the nozzle element 20, the outlet cross-section decreases. When the needle is withdrawn from the nozzle assembly 10 or the nozzle element 20, the outlet cross-section increases.

[0048] In Fig. As can be seen in Figure 1, the nozzle assembly 10, more precisely the bearing 11 of the needle 30, has a recess 24 extending along the length of the needle 30 on a cylindrical bearing bore 13, which is designed as an axial groove. The recess 24 is thus arranged on the bearing bore 13 of the nozzle assembly 10. The recess 24 essentially forms a vent bore towards the actuator 4 and a reduction in the shear area with respect to the needle 30, which cannot be changed by adjusting the needle 30 or results independently of the adjustment of the needle 30. In this respect, the recess 24 provides a fluidic connection between one side of the bearing bore 13 in the nozzle assembly 10 and the other side of the bearing bore 13. In this case, the needle 30 does not engage radially in the recess 24. The needle 30 covers the recess 24 in the radial direction.An additional bore with reference numeral 25 extends along the needle 30 and is arranged next to the bearing bore 13, primarily as a cylindrical bore. This bore 25 essentially also serves as a vent bore, but in this case not for reducing the shear area with respect to the needle 30. Water or condensate can drain through the recess 24 and the bore 25, thus reducing the risk of the jet pump 2 freezing.

[0049] Several recesses 24 and bores 25 are provided. The recesses 24 and bores 25 are arranged or provided in the bearing 11 of the needle 30, preferably spaced equally apart from each other in the circumferential direction.

[0050] The nozzle assembly 10, in particular the bearing 11 of the needle 30 and / or the nozzle element 20, has a coating, in this case made of carbon or as a C+ layer. The nozzle assembly 10, more precisely a conical section 14 of the nozzle carrier 12 and a conical section 22 of the nozzle element 20, tapers downstream and along the needle 30. The conical sections 14 and 22 merge flush into one another. A change in the taper angle can be provided between the conical sections 14 and 22, as is the case here. In particular, the conical section 22 in the nozzle element 20 is shallower in the axial direction than the conical section 14 of the nozzle carrier 12. The cylindrical section of the nozzle element 20 adjoins the conical section 22 downstream. Opposite the nozzle element 20 or the outlet cross-section, the bearing 11 of the needle 30 or the bearing bore 13 is arranged, as are the recesses 24 and bores 25.

[0051] A mixing tube 40, forming the mixing chamber 42, is attached to the nozzle assembly 10. Downstream of the nozzle assembly 10, a cylindrical section 44 and, adjacent to this, a conically expanding section 46 of the mixing tube 40 are provided.

[0052] The nozzle assembly 10 further comprises a feed 16 for supplying a fluid, for example hydrogen, in particular fresh hydrogen, and a suction side 18 for drawing in a fluid, for example recirculating hydrogen, or forms such a side.

[0053] The suction side 18 is arranged on the nozzle assembly 10 such that, in the case of a downstream fluid flow or a fluid flow from the outlet cross-section, a recirculating fluid can be drawn in through the suction side 18. The flow from the outlet cross-section thus creates a negative pressure at the suction side 18, which serves for suction.

[0054] The jet pump 2 shown is designed to supply a fluid or hydrogen to the mixing chamber 42 via the nozzle assembly 10.

[0055] The nozzle element 20 is attached to or embedded in the nozzle carrier 12 in a material-bonded and gas-tight and / or vibration-proof manner. More precisely, the nozzle element 20 is overmolded by the nozzle carrier 12 and / or embedded in it. It is also conceivable that the nozzle element 20 is inserted into the nozzle carrier 12. For example, the nozzle element 20 can be screwed, pressed, and / or glued into the nozzle carrier 12.

[0056] The bearing 11 of the needle 30 is attached to or received in the nozzle carrier 12, in particular by means of a force-fit connection. For example, the bearing 11 of the needle 30 can be screwed, clamped, pressed in, and / or glued into the nozzle carrier 12. The bearing 11 of the needle 30 is made of metal. The bearing bore 13 has a diameter that essentially corresponds to the outer diameter of the needle 30.

[0057] The suction side 18 opens around the nozzle assembly 10 or the nozzle element 20 for the recirculation of hydrogen and to be mixed with hydrogen exiting the nozzle assembly 10.

[0058] The actuator 4 for actuating the needle 30 is located adjacent to the bearing 11 of the needle 30 on the nozzle assembly 10.

[0059] Fig. Figure 2 shows an embodiment of a jet pump 2, only partially depicted, in a longitudinal section view ( Fig. 2A) and in a perspective view of only one bearing 11 of the needle 30 ( Fig. 2B), in which two bores 25 extending along a needle 30 are provided next to a bearing bore 13, shown here without at least one recess 24.

[0060] The needle 30 is guided away from its tip 32 in a cylindrical bearing bore 13, and two bores 25 are provided radially spaced from it. The bores 25 are designed as cylindrical bores 25 that run parallel to the needle 30 and the bearing bore 13, respectively. The bores 25 essentially serve as venting bores.

[0061] Fig. Figure 3 shows an embodiment of a jet pump 2, only partially depicted, in a longitudinal section view ( Fig. 3A) and in a perspective view of only one bearing 11 of the needle 30 ( Fig.3B), in which three recesses 24 extending along a needle 30 are provided at a bearing bore 13.

[0062] The needle 30 is guided away from its tip 32 in a substantially cylindrical bearing bore 13, the three recesses 24 being part of the bearing bore 13 itself and reducing its shear area together with the needle 30. The recesses 24 are designed as radial cutouts that run parallel to the needle 30 and the bearing bore 13. The recesses 24 serve essentially as venting holes and for reducing the shear area. Reference symbol list 2 jet pumps 4 Actuator 10 nozzle assembly 11. Needle storage 12 nozzle carriers 13 bearing bore 14 conical section 16 Feed 18 Suction side 20 nozzle elements 22 conical section 24 In-depth study 25 bore 30 needles 32 peak 40 mixing tube 42 Mixing chamber 44 cylindrical section 46 conical section or diffuser

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