EJECTOR HAVING AN ACTUATION MECHANISM WITH A PILOT VALVE AND AN EQUALIZATION PASSAGE BETWEEN TWO CYLINDER CHAMBERS

Abstract

An ejector (1; 100), e.g. for a refrigerant circuit, with a primary inlet (2), a secondary inlet (7), an outlet (12), a nozzle (5), and a mixing portion (6, 10) includes an actuating mechanism (30) moving a needle (20) between an opened position and a closed position. The actuation mechanism (30) includes a piston (31) in a cylinder (35), wherein a first cylinder chamber (37) is in fluid communication with the primary inlet (2) and a second cylinder chamber (38) is in fluid communication with the first cylinder chamber (37). The second cylinder chamber (38) is in fluid communication with the secondary inlet (7) and/or the outlet (12) via a drain passage (39, 53, 54, 55, 56, 57) when a pilot valve (50) arranged in the drain passage (39, 53, 54, 55, 56, 57) is in an open state. For ensuring smooth opening and closing, the fluid communication of the second cylinder chamber (38) with the first cylinder chamber (37) is provided by an equalization passage (32), wherein a flow cross-section of the equalization passage (32) is larger than a flow cross-section of the drain passage (39, 53, 54, 55, 56, 57).

Claims

1. An ejector comprising a primary inlet; a secondary inlet; and an outlet; a nozzle for jetting fluid supplied at the primary inlet into a mixing portion for sucking fluid supplied at the secondary inlet into the mixing portion); a needle and a needle seat, wherein the needle seat is arranged downstream of the primary inlet and upstream of the nozzle; and an actuating mechanism for moving the needle between an opened position, in which the needle is lifted from the needle seat for allowing fluid flow past the needle seat, and a closed position, in which the needle abuts the needle seat and blocks fluid flow past the needle seat, wherein the actuating mechanism comprises: a cylinder with a piston connected to the needle, wherein a first cylinder chamber is maximized when the needle is in its opened position and a second cylinder chamber is maximized when the needle is in its closed position, wherein the first cylinder chamber is in fluid communication with the primary inlet via a chamber inlet, and wherein the second cylinder chamber is in fluid communication with the first cylinder chamber, and a drain passage with a pilot valve, wherein the second cylinder chamber is in fluid communication with the secondary inlet and/or the outlet via the drain passage when the pilot valve is in an open state, wherein the fluid communication of the second cylinder chamber with the first cylinder chamber is provided by an equalization passage, wherein a flow cross-section of the equalization passage is larger than a flow cross-section of the drain passage.

2. The ejector according to claim 1, wherein a piston area, which is a cross-section area of the piston, is at least 1000 times the flow cross-section of the equalization passage.

3. The ejector according to claim 1, wherein a needle seat area, which is a cross-section area of the needle seat where the needle engages the needle seat in the closed position, is in the range from 1,005 to 1,4 times a flow cross-section of the nozzle.

4. The ejector according to claim 1, wherein the pilot valve is a solenoid valve.

5. The ejector according to claim 1, wherein the piston area corresponds to at least 20 times the needle seat area.

6. The ejector according to claim 1, wherein a stroke(S) of the needle between the closed position and the opened position correspond to at least 2*(A.sub.noz/).sup.0,5, where A.sub.noz is the flow cross-section of the nozzle.

7. The ejector according to claim 1, wherein the ejector includes a check valve for preventing fluid flow from the outlet to the secondary inlet.

8. The ejector according to claim 1, wherein the equalization passage is formed in the piston.

9. The ejector according to claim 1, wherein the flow cross-section of the equalization passage is in the range from 1,2 to 2,5 times the flow cross-section of the drain passage when the pilot valve is in an open state.

10. The ejector according to claim 1, wherein a nozzle inlet is formed directly upstream of the nozzle, wherein the nozzle inlet tapers toward the nozzle, wherein the needle seat is located in the nozzle inlet, and wherein a length (W) of the nozzle inlet corresponds to at least 1,8 times the stroke (S) of the needle between the closed position and the opened position.

11. The ejector according to claim 1, wherein the ejector comprises a resilient member acting against minimizing the second cylinder chamber by the piston.

12. The ejector according to claim 1, wherein the ejector is configured such that an opening time of the needle is at least 0,5 s and/or that a closing time of the needle is at least 1 s.

13. The ejector according to claim 1, wherein the flow cross-section of the nozzle is at least 50 mm.sup.2.

14. The ejector according to claim 1, wherein the cylinder is formed by a cylinder insert and a top cover, wherein an elastic member biases the cylinder insert in abutment against the top cover.

15. An ejector assembly comprising at least two ejectors according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 shows an embodiment of an ejector according to the present invention in an open state in a cross-sectional view on a plane extending along a central axis of the ejector;

[0073] FIG. 2 is an enlarged upper section of FIG. 1;

[0074] FIG. 3 shows the upper part of the ejector of FIG. 2 in a cross-sectional view on a plane, which extends along the central axis of the ejector as well but is perpendicular to the plane shown in FIG. 1 and FIG. 2;

[0075] FIG. 4 shows an enlarged section of FIG. 1 around a needle seat and a nozzle,

[0076] FIG. 5 shows a second embodiment of an ejector according to the present invention in an open state in a cross-sectional view on a plane extending along a central axis of the ejector: and

[0077] FIG. 6 is a magnified section of FIG. 5 around a needle tip.

DETAILED DESCRIPTION

[0078] An embodiment of an ejector 1 according to the present invention is shown in FIG. 1. The ejector 1 comprises a primary (fluid) inlet 2, a secondary (fluid) inlet 7, and an (fluid) outlet 12. The primary inlet 2 may be also referred to as high pressure inlet 2. The ejector 1 extends along a central axis C. A longitudinal direction L is parallel to the central axis C.

[0079] If the ejector 1 is in an open state as shown in FIGS. 1 to 4, fluid can flow from the first inlet 2 through a nozzle 5, a mixing portion (which includes a convergent mixing portion 6 and a cylindrical mixing portion 10), and a diffuser portion 11 to the fluid outlet 12. In addition, fluid is drawn from the secondary inlet 7 into the mixing portion 6. In other words, the fluid drawn from the secondary inlet 7 joins the fluid from the primary inlet 2 in the convergent mixing portion 6. This results in mixing of the fluid from the primary inlet 2 and the fluid drawn from the secondary inlet 7 in the convergent mixing portion 6 and the cylindrical mixing portion 10 that follows downstream of the convergent mixing portion 6.

[0080] The ejector 1 includes a needle valve mechanism with a needle 20 and a needle seat 26.

[0081] If the needle 20 is in a closed position (not shown), it abuts the needle seat 26 and blocks the fluid connection between the primary inlet 1 and the nozzle 5. This prevents that fluid from the primary inlet 1 can enter into the nozzle 5 and flow further into the convergent mixing portion 6. This corresponds to a closed state of ejector 1.

[0082] If the needle 20 is in an opened position as shown in FIGS. 1 to 4, the needle 20 is lifted from the needle seat 26 by a needle stroke S (see FIG. 4). This allows fluid flow from the primary inlet 2 into the nozzle 5. The stroke S is the displacement of the needle 20 along the longitudinal direction L between its opened position and its closed position. The stroke S may be at least 10 mm, for example in the range from 12 mm to 30 mm.

[0083] In this exemplary embodiment, a housing 70 of the ejector 1 includes a main sleeve 71, an upstreamside top cover 76, a first diffuser tube 74, and a second diffuser tube 75. The first diffuser tube 74 and the second diffuser tube 75 form at least a downstream part of the diffuser portion 11. The housing 70 further includes a primary (fluid) inlet connector 72, which is fixed to the main sleeve 71 and forms the primary inlet 2, and a secondary (fluid) inlet connector 73, which is fixed to the main sleeve 71 and forms the secondary inlet 7.

[0084] The ejector 1 further comprises an actuating mechanism 30 for moving the needle 20 along the longitudinal direction L between the opened position and the closed position.

[0085] The actuating mechanism 30 comprises a pilot valve 50 and a piston 31. The piston 31 is arranged in a cylinder 35 and can be axially displaced within the cylinder 35 (i.e. along the central axis C). The needle 20 is mechanically connected to the piston 31 such that the axial movement of the piston 31 in the cylinder 35 is transferred to movement of the needle 20 along the longitudinal direction L. Accordingly, the needle 20 can be moved from its opened position to its closed position and vice versa by corresponding axial movements of the piston 31. In this embodiment, the needle 20, the piston 31, and the cylinder 35 are all arranged coaxially along the central axis C and the needle 20 is at least axially fixed to the piston 31. In more detail, the needle 20 and the piston 31 can be formed integrally (in one piece) as shown in FIGS. 1 to 3. In other words, the needle 20 (in particular a needle stem 25) also constitutes a piston rod for the piston 31.

[0086] The cylinder 35 can be formed by a cylinder insert 77 and the top cover 76 as shown in FIGS. 1 to 3. The cylinder insert 77 is arranged in an interior of the main sleeve 71 and directly abuts the top cover 76. The cylinder insert 77 guides the piston 31 and its piston rod (which is the needle 20 in this embodiment).

[0087] The piston 31 is configured to form a first cylinder chamber 37 and a second cylinder chamber 38 within the cylinder 35. It can divide an interior of the cylinder 35 into the first cylinder chamber 37 and the second cylinder chamber 38 (along the longitudinal direction L).

[0088] A volume of the first cylinder chamber 37 is maximized (maximal) when the needle 20 is in its opened position. It is minimized when the needle 20 is in its closed position. It may decrease (at least substantially) to a minimum volume (small residual volume) when the needle 20 is in its closed position (not shown, corresponds to a lowermost possible position of the piston 31 in FIGS. 1 to 3).

[0089] A volume of the second cylinder chamber 38 is maximized (maximal) if the needle 20 is in its closed position. It is minimized when the needle 20 is in its opened position (correspond to an uppermost possible position of the piston 31 as shown in FIGS. 1 to 3). It may decrease (at least substantially) to zero when the needle 20 is in its opened position. However, in the exemplary embodiment, an annular end wall 40, which is provided on a surface of the piston 31 facing the second cylinder chamber 38, causes that a residual volume of the second cylinder chamber 38 remains even if the needle 20 is in its opened position. This ensures that the equalization passage 32 is not closed when the needle 20 is in the opened position.

[0090] At a side of the cylinder insert 77 in the longitudinal direction L that faces away from the top cover 76, a primary (fluid) inlet chamber 3 is formed. The primary inlet connector 72 opens into the primary inlet chamber 3.

[0091] The first cylinder chamber 37 is in fluid communication with the primary inlet 2 via a chamber inlet 36. In this embodiment, the chamber inlet 36 is a fluid connection provided between the primary inlet chamber 3 and an end of the cylinder 35 in the longitudinal direction L at the side of the needle 20 (an end of the cylinder 35 at the side of the first cylinder chamber 37, i.e. a lower end of the cylinder 35 in FIGS. 1 to 3). The chamber inlet 36 may be formed in the cylinder insert 77, for example as at least one bore extending along the longitudinal direction L. In the embodiment shown in FIGS. 1 and 2, four or six of such bores are formed in the cylinder insert 77. Two of them can be seen in FIGS. 1 and 2.

[0092] Further, the other end of the cylinder 35 in the longitudinal direction L (an end of the cylinder 35 at the side of the second cylinder chamber 38, i.e. an upper end of the cylinder 35 in FIGS. 1 to 3) is in fluid communication with the secondary inlet 7 via a drain passage. The pilot valve 50 is arranged in the drain passage. When the pilot valve 50 is in its closed state, it blocks (closes) the drain passage. When the pilot valve 50 is in its open state, the drain passage is open and the second cylinder chamber 38 is in fluid communication with the secondary inlet 7. In other words, the drain passage is formed between the second cylinder chamber 38 on the one hand and, on the other hand, the secondary inlet 7 and/or a space that is in (direct) fluid communication with the secondary inlet 7. In this embodiment, the drain passage is formed between the second cylinder chamber 38 and a secondary (fluid) inlet chamber 8, which is in direct fluid communication with the secondary inlet 7.

[0093] In a modification (not shown), the second cylinder chamber 38 is in fluid communication with the outlet 12 via the drain passage when the pilot valve 50 is in an open state. In other words, the drain passage with the solenoid valve 50 is formed between the second cylinder chamber 38 and the fluid outlet 12 and/or a space that is in fluid communication with the fluid outlet 12 in this case. Of course, it is also possible to provide a drain passage with two branches, one branch for fluid communication of the second cylinder chamber 38 with the secondary inlet 7 and another branch for fluid communication of the second cylinder chamber 38 with the fluid outlet 12. A blocking means, e.g. a check valve, can be employed to prevent fluid flow from the secondary inlet 7 to the fluid outlet 12 via the drain passage.

[0094] As shown in FIG. 1, the drain passage may be formed completely within the ejector 1. It is integrated in the ejector 1 as such.

[0095] Turning now to FIG. 3, the drain passage includes a fluid connection 39 between the upper end of the cylinder 35 (the second cylinder chamber 38) and an upstream side of the pilot valve 50. Said fluid connection 39 may be also referred to as the chamber outlet 39. As can be seen in FIG. 3, the chamber outlet 39 may be formed by at least one channel, for example two channels, within the top cover 76.

[0096] Further, a downstream side of the pilot valve 50 is in fluid communication with the secondary inlet 7. This can be seen in FIGS. 1 and 2, where the plane of the depicted cross-section is perpendicular to the one shown in FIG. 3. In the present embodiment, the drain passage includes a first fluid passage 54 formed in the top cover 76, a second fluid passage 55 that is also formed in the top cover 76, a fluid passage 56 formed in the main sleeve 71, and a fluid passage 57 formed between the main sleeve 71 and an insert assembly holder 78. The fluid passage 57 is a substantially annular gap between the main sleeve 71 and the insert assembly holder 78. The drain passage opens into the secondary inlet chamber 8. The secondary inlet connector 73 also opens into the secondary inlet chamber 8. Hence, the downstream side of the pilot valve 50 is in fluid communication with the secondary inlet 7, and the second cylinder chamber 38 is in fluid communication with the secondary inlet 7 when the pilot valve 50 is in its open state.

[0097] In addition, the second cylinder chamber 38 is in fluid communication with the first cylinder chamber 37. The fluid communication is provided by an equalization passage 32. In this embodiment, the equalization passage 32 includes longitudinal bore through the piston 31. The equalization passage 32 may be formed completely within the ejector 1. It is integrated in the ejector 1 as such.

[0098] The pilot valve 50 includes a valve seat 51, a valve member 52, and an actuator 53. The actuator 53 is configured to switch the pilot valve 50 between an open state and a closed state thereof. In this embodiment, the pilot valve 50 is a solenoid valve. Hence, the actuator 53 is a solenoid actuator. The pilot valve 50 is a part of the ejector 1. In particular, the valve seat 51 may be integrally formed with the housing 70 or an insert fixed to the housing. In the exemplary embodiment, the valve seat 51 is mounted within the top cover 76.

[0099] In the following, the operation will be described. It is assumed that the needle 20 is in its opened position and that the pilot valve 50 is in its open state at the beginning. In other words, the ejector 1 is in its open state at the beginning.

[0100] In normal operation, fluid is supplied at the primary inlet 2 with a high primary pressure. Consequently, high-pressure fluid from the primary inlet 2 flows through the chamber inlet 36 into the first cylinder chamber 37. A (minimum) flow cross-section A.sub.pci of the chamber inlet 36 is larger than a (minimum) flow cross-section A.sub.eq of the equalization passage 32. For example, the flow cross-section A.sub.pci of the chamber inlet 36 may be at least 5 times, especially at least 10 times, the flow cross-section A.sub.eq of the equalization passage 32. In the exemplary embodiment shown in FIG. 1, the flow cross-section A.sub.pci of the chamber inlet 36 is the sum of the cross-sectional areas of the bores constituting the chamber inlet 36, which are formed in the cylinder insert 77.

[0101] Due to the chamber inlet 36, the fluid pressure in the first cylinder chamber 37 at least substantially corresponds to the primary pressure at the primary inlet 2. The fluid pressure in the first cylinder chamber 37 forces the piston 31 (along the longitudinal direction L) towards the top cover 76 and hence the needle 20 towards its opened position, against a resilient force provided by a resilient member 33. In the depicted embodiment, the resilient member 33 is a coil spring.

[0102] In normal operation, fluid is supplied at the secondary inlet 7 with a secondary pressure. The secondary pressure is less than the primary pressure at the primary inlet 2 but higher than an outlet pressure at the fluid outlet 12. In other words, there is a pressure drop from the primary pressure to the secondary pressure. This pressure drop is used for jetting the fluid from the primary inlet chamber 3 through the nozzle 5 into the convergent mixing portion 6 when the needle 20 is in its opened position. The fluid jetted out of the nozzle 5 has a high velocity. The ejection through the nozzle 5 results in a pressure drop from the primary inlet chamber 3 to the convergent mixing portion 6. Further, when the needle 20 is in its opened position such that fluid from provided at the primary inlet 2 is jetted out of the nozzle 5, fluid provided at the secondary inlet 7 is sucked from the secondary inlet chamber 8 through a secondary fluid passageway 9 into the convergent mixing portion 6. The fluid from the primary inlet 2, which is ejected by the nozzle 5, and the fluid sucked from the secondary inlet chamber 8 mix in the convergent mixing portion 6 and the cylindrical mixing portion 10.

[0103] As noted above, it is assumed that the pilot valve 50 is in its open state at the beginning. A small fluid flow from the first cylinder chamber 37 to the second cylinder chamber 38 via the equalization passage 32 occurs. Furthermore, fluid flows from the second cylinder chamber 38 to the secondary inlet chamber 8 via the drain passage because the pilot valve 50 is in its open state. Hence, there is a small pressure drop from the first cylinder chamber 37 to the second cylinder chamber 38 which is sufficient for keeping the needle 20 in the opened position. The pressure drop is sufficiently high for holding the piston 31 in abutment with the top cover 76 against the restoring force of the resilient element 33.

[0104] The flow cross-section A.sub.eq of the equalization passage 32 is comparatively small. It may be less than 10 mm.sup.2, e.g. in the range from 0,5 mm.sup.2 to 4 mm.sup.2. Additionally or alternatively, a value corresponding to the square of a length L.sub.eq of the equalization passage 32 (along a flow direction therethrough) may be at least 15 times, for example at least 25 times, the flow cross-section A.sub.eq of the equalization passage 32 (L.sub.eq.sup.215*A.sub.eq). The equalization passage 32 exhibits considerable flow resistance.

[0105] If the equalization passage 32 has a cylindrical shape, its flow cross-section A.sub.eq is *(D.sub.eq/2).sup.2, wherein D.sub.eq is a diameter of the equalization passage 32.

[0106] In general, the flow cross-section A.sub.eq of the equalization passage 32 can be larger or the same as a (minimum) flow cross-section A.sub.dp of the drain passage (when the pilot valve 50 is in its open state).

[0107] When the ejector 1 is in the open state, an intermediate pressure occurs in the second cylinder chamber 38. The intermediate pressure is lower than the pressure in the first cylinder chamber 37 (which may at least substantially correspond to the primary pressure). The intermediate pressure is larger than the secondary pressure. The exact value of the intermediate pressure depends, inter alia, on the flow resistance and hence on the flow cross-section A.sub.eq of the equalization passage 32 as well as on a flow resistance and hence on the flow cross-section A.sub.dp of the drain passage and on a ratio A.sub.eq/A.sub.dp.

[0108] If the flow cross-section A.sub.eq of the equalization passage 32 is considerably smaller than the flow cross-section A.sub.dp of the drain passage (A.sub.eq/A.sub.dp<<1), the flow resistance of the drain passage is considerably smaller than the flow resistance of the equalization passage 32. When the pilot valve 50 is open, fluid can be discharged from the second cylinder chamber 38 into the secondary inlet chamber 8 through the drain passage in an almost unobstructed manner. The intermediate pressure in the second cylinder chamber 38 will become almost as low as the secondary pressure if the pilot valve 50 is in its open state.

[0109] However, according to one aspect of the present disclosure, the flow cross-section A.sub.eq of the equalization passage 32 may be larger than the flow cross-section A.sub.dp of the drain passage (A.sub.eq/A.sub.dp>1). Especially, the flow cross-section A.sub.eq of the equalization passage 32 may be in the range from 1,2 to 2,5 times the flow cross-section A.sub.dp of the drain passage (1,2*A.sub.dpA.sub.eq2,5*A.sub.dp). The flow resistance of the equalization passage 32 is smaller than the flow resistance of the drain passage. However, the pressuredrop from first cylinder chamber 37 to the second cylinder chamber 38 is smaller in that case. Nevertheless, the intermediate pressure in the second cylinder chamber 38 is less than pressure in the first cylinder chamber 37 when the pilot valve 50 is in its open state. In other words, there is nevertheless the small pressure drop. The small pressure drop remains due to the flow resistance exhibited by the equalization passage 32 and due to ongoing discharge of fluid out of the second cylinder chamber 38. For example, the ejector 1 may be configured such that a pressure drop from the first cylinder chamber 37 to the second cylinder chamber 38 (i.e. a pressure drop along the equalization passage 32) is less than 10 bar, especially less than 3 bar, in normal operation if the pilot valve 50 after the pilot valve 50 is open for at least 0,2 s. This ensures a smooth transition from the closed position of the needle 20 to its opened position (and hence a smooth transition from the closed state of the ejector 1 to the open state of the ejector 1) even if the actuating mechanism is controlled by a solenoid valve.

[0110] Accordingly, the ejector 1 may be configured such that an opening time of the needle 20 is at least 0,5 s in normal operation, especially at least 1 s. The opening time may be a time needed for the movement of the needle 20 from its closed position to its opened position in normal operation.

[0111] The (minimum) flow cross-section A.sub.dp of the drain passage may correspond to a flow cross-section A.sub.pv of the pilot valve 50 when the pilot valve 50 is in its open state.

[0112] Starting from the situation that the needle 20 is in its opened position and that the pilot valve 50 is open, as long as the pilot valve 50 remains opened, the intermediate pressure is less than the pressure in the first cylinder chamber 37. The needle 20 is kept in its opened position while the pilot valve 50 remains open. The ejector 1 is configured such that, in this situation, the force on the piston 31 resulting from the pressure difference between the intermediate pressure in the second cylinder chamber 38 and the pressure in the first cylinder chamber 37 is sufficient to (at least substantially) overcome the resilient force of the spring 33.

[0113] Now it is assumed that the pilot valve 50 is closed in this situation. No more fluid can be drained from the second cylinder chamber 38 to the secondary inlet chamber 8. As the equalization passage 32 remains open, the pressure in the second cylinder chamber 38 increases towards the pressure in the first cylinder chamber 37 (which may at least substantially correspond to the primary pressure). In addition, the resilient member 33 urges the piston 31 away from the top cover 76. The piston 31 start to move along the longitudinal direction L towards the needle seat 26. Accordingly, the needle 20 starts to move along the longitudinal direction L towards the needle seat 26 (i.e. towards its closed position).

[0114] The flow cross-section A.sub.eq of the equalization passage 32 is small compared to a piston area Ap of the piston 31. The piston area A.sub.P may correspond to at least 1000 times, e.g. to at least 1600 times, especially to at least 2100 times, the flow cross-section A.sub.eq of the equalization passage 32. This limits a movement speed of the piston 31.

[0115] This ensures a smooth transition from the opened position of the needle 20 to its closed position (and hence a smooth transition from the open state of the ejector 1 to the closed state of the ejector 1) even if the actuating mechanism is controlled by a solenoid valve that can only be switched between the open state and the closed state and does not provide a possibility to adjust any opening degree inbetween.

[0116] The ejector 1 may be configured such that a closing time of the needle 20 is at least 1 s in normal operation, especially at least 2 s. The closing time may be a time needed for the movement of the needle 20 from its opened position to its closed position in normal operation.

[0117] For example, the piston area AP can be in the range from 2000 mm.sup.2 to 10000 mm.sup.2.

[0118] If the piston 31 has a rotationally symmetric basic shape, its flow cross-section A.sub.p is *(D.sub.p/2).sup.2, wherein D.sub.p is a diameter of the piston 31.

[0119] At the end of the transition from the open state of the ejector 1 to its closed state, the needle 20 abuts the needle seat 26. The fluid connection from the primary inlet chamber 3 to the nozzle 5 (and hence from the primary inlet 2 to the nozzle 5) is blocked. No more fluid is ejected by the nozzle 5. Accordingly, no further fluid is sucked from the secondary inlet 7 into the convergent mixing portion 6.

[0120] In order to bring the ejector 1 from its closed state to its open state again, the pilot valve 50 is opened again. Fluid is discharged from the second cylinder chamber 38 to the secondary inlet chamber 8 and the pressure in the second cylinder chamber 38 decreases towards the intermediate pressure mentioned above. Due to the pressure drop from the first cylinder chamber 37 and the second cylinder chamber 38, the piston 31 starts to move along the longitudinal direction L such that the needle 20 is retracted from the needle seat 26 towards the opened position.

[0121] A cross-sectional area A.sub.nsz of the needle seat 26 (a needle seat area A.sub.ns) is only a bit larger than a (minimum) flow-cross section A.sub.noz of the nozzle 5. In particular, the needle seat area A.sub.nsz may be in the range from 1,005 to 1,4 times the flow-cross section A.sub.noz of the nozzle 5. This allows for the needle 20 having a small diameter. Hence, a flow resistance for fluid flowing from the primary inlet 2 to the nozzle 5 if the needle 20 is in its opened position is particularly low. Furthermore, the comparatively small needle seat area A.sub.nsz ensures smooth and precise beginning of the transition from the closed position of the needle 20 to its opened position.

[0122] Typically, an increased initial force is required for starting the transition from the closed position to the opening position (i.e. from retracting the needle 20 from the closed position, particularly from abutment with the needle seat 26). The force needed for further retraction of the needle 20 may decline. The initial force depends, inter alia, on a size of a contact area between the needle 20 and the needle seat 26. The initial force must be provided by the actuating mechanism 30. It is beneficial that the needle seat area A.sub.nsz is as close as possible to the flow-cross section A.sub.noz of the nozzle 5. This reduces the required initial force. As a consequence, a smaller and less expensive actuating mechanism 30 can be used.

[0123] Furthermore, the small needle seat area Ans reduces the risk of unintentional liftoff of the needle 20 from the needle seat 26 in the case of pressure peaks applied from the secondary inlet 7 and our the outlet 12.

[0124] If the nozzle 5 is formed rotationally symmetric, its flow cross-section A.sub.noz is *(D.sub.noz/2).sup.2, wherein D.sub.noz is a minimum inner diameter of the nozzle 5. If the needle seat 26 has a circle-shape, the needle seat area A.sub.nsz is the area encircled by the needle seat 26 and corresponds to *(D.sub.ns/2).sup.2, wherein D.sub.ns is a diameter of the needle seat 26.

[0125] The flow cross-section A.sub.noz can be at least 50 mm.sup.2. This corresponds to a diameter of 8,0 mm if the nozzle 5 is formed rotationally symmetric. For example, the flow cross-section A.sub.noz of the nozzle 5 can be in the range from 70 mm.sup.2 to 150 mm.sup.2.

[0126] FIG. 4 shows that, in this exemplary embodiment, an end portion of the needle 20 at the side of the needle seat 26 includes, seen along the longitudinal direction L, a needle tip 21, a first conical needle portion 22, and a second conical needle portion 24. A taper angle of the first conical needle portion 22 is larger than a taper angle of the second conical needle portion 24. Hence, an annular edge 23 is formed at the border between the first conical needle portion 22 to the second conical needle portion 24. (Only) the annular edge 23 abuts onto the needle seat 26 when the needle 20 is in its closed position.

[0127] The needle 20 can be made of Aluminum or an aluminum alloy.

[0128] In the depicted embodiment, the flow resistance of the drain passage is larger than the flow resistance of the equalization passage 32. This helps to ensure slow and controlled opening of the ejector 1. Especially, the flow cross-section A.sub.pv of the pilot valve 50 may be smaller than the flow cross-section A.sub.eq of the equalization passage 32. Additionally or alternatively, the flow cross-section A.sub.pv of the pilot valve 50 (in its open state) may be less than 1,8 mm.sup.2.

[0129] The piston area A.sub.P of the piston 31 may be larger than a squared value of a stroke of the piston rod. In this example, the stroke of the piston rod is the same as the stroke S of the needle 20. For example, the piston area A.sub.P may correspond to at least 8 times, especially at least 11 times, the squared value of the stroke S (A.sub.P8*S.sup.2, especially A.sub.P11*S.sup.2). Hence, the axial displacement of the piston 31 by the stroke S corresponds to a large change of the volumes of the first cylinder chamber 37 and the second cylinder chamber 38. This helps to ensure slow movement of the piston 31 and hence the needle 20 during transitions between the opened position and the closed position. Moreover, a pronounced synergistic effect can be obtained by combining this aspect with the aspect explained above, according to which the flow cross-section A.sub.eq of the equalization passage 32 may be small compared to the piston area A.sub.P of the piston 31.

[0130] Additionally or alternatively, the piston area A.sub.P of the piston 31 may be large compared to the needle seat area A.sub.ns. This reduces the influence of the additional lifting force on the opening and results in smoother opening.

[0131] The nozzle 5 is formed directly downstream of a nozzle inlet 4. The nozzle inlet 4 extends the longitudinal direction L and tapers towards the nozzle 5. In more detail, it may extend along the central axis C as in the figures.

[0132] An annular, line-shaped portion of the nozzle inlet 4, onto which the annular edge 23 abuts when the needle 20 is in its closed position, constitutes the needle seat 26.

[0133] The nozzle inlet 4 is configured to guide the fluid supplied at the primary inlet 2 into the nozzle 5. More precisely, it guides the fluid supplied at the primary inlet 2 from the primary inlet chamber 3 into the nozzle 5 (when the needle 20 is in its opened position).

[0134] The nozzle inlet 4 can be a conical nozzle inlet. A taper angle of the nozzle inlet 4 is smaller than the taper angle of the first conical needle portion 22 but larger than the taper angle of the second conical needle portion 24 (e.g., see FIG. 4).

[0135] In this exemplary embodiment, the needle seat 26 and the nozzle 5 are formed in the same component, namely in a nozzle insert 27. The nozzle insert 27 is a one-piece component. It is mounted in the insert assembly holder 78. The nozzle insert 27 includes the upstream nozzle inlet 4 and the nozzle 5. The nozzle insert 27 can be made of a material having a higher hardness than a material of the needle 20.

[0136] For example, the nozzle insert 27 can be made of iron.

[0137] According to another aspect, a length W of the nozzle inlet 4 is larger than the stroke S. For example, the length of the nozzle inlet 4 may correspond to at least 1,8 times the stroke S. This ensures that the end portion of the needle 20 still protrudes into the nozzle inlet 4 even if the needle 20 is in its opened position. Accordingly, the needle 20 helps, in its opened position, to guide the fluid from the primary inlet chamber 3 smoothly into the nozzle inlet 4 and further into the nozzle 5 and to reduce turbulences.

[0138] A distance Z between the nozzle 5 and the needle seat 26 along the longitudinal direction L (and according to a local flow direction) is small. It may be less than 0,8*(A.sub.noz/).sup.0,5. In other words, the needle seat 26 may be formed directly upstream of the nozzle 5. This facilitates to keep the needle seat area A.sub.nsz small and to reduce the flow resistance.

[0139] Additionally or alternatively, the stroke S may correspond to at least 2*(A.sub.noz/).sup.0,5, which corresponds to the D.sub.noz if the nozzle is of rotationally symmetric shape. Especially, the stroke S may correspond to at least 2,8*(A.sub.noz/).sup.0,5. As a consequence, the end portion of the needle 20 does not impair fluid flow through the nozzle 5 or the needle seat 20 in its opened position.

[0140] The ejector 1 may be configured such that the flow cross-section A.sub.noz of the nozzle 5 constitutes a minimum flow cross-section between the primary inlet 2 and the convergent mixing portion 6 when the needle 20 is in its opened position.

[0141] In the exemplary embodiment, the needle 20 never protrudes downstream of the nozzle 5. In other words, the needle 20 never protrudes into the convergent mixing portion 6.

[0142] As an additional feature, the depicted embodiment of the ejector 1 provides a check valve functionality for preventing fluid flow from the outlet 12 to the secondary inlet 7. The ejector 1 provides a check member 80 for closing a fluid connection between the mixing portion (in more detail, the convergent mixing portion 6) and the secondary inlet chamber 8. If the ejector 1 is in its closed state, the check member 80 abuts on a check valve seat 79 and blocks fluid flow from the outlet 12 to the secondary inlet 7. If the ejector 1 is in its open state, fluid is sucked from the secondary inlet 7 through the secondary inlet chamber 3 and the secondary fluid passageway 9 into the convergent mixing portion 6. Thereby, the check member 80 is displaced along the longitudinal direction L and lifts off from the check valve seat 79.

[0143] An annular end face of the cylinder insert 77 and a corresponding abutment area on the top cover 76 are grounded flat. An elastic member 90 (which is a coil spring in this embodiment) biases the cylinder insert 77 against the top cover. Hence, no significant fluid leakage or pressure propagation can occur directly from the primary inlet chamber 3 to the second cylinder chamber 38. The elastic member 90 is arranged in the primary inlet chamber 3 and coaxially to the needle 20. It is squeezed between the top cover 76 and the insert assembly holder 78.

[0144] Optionally, a filter 91 is provided between the primary inlet 2 and the nozzle inlet 4. In the exemplary embodiment, the filter 91 is provided in the primary inlet chamber 3 around the elastic member 90, wherein the elastic member supports (backs up) the filter 91.

[0145] The top cover 76 is removably fixed to the main sleeve 71 by screws. If the top cover 76 is detached, the cylinder insert 76 can be taken out of the main sleeve 71 for maintenance.

[0146] Naturally, the depicted embodiment is only an exemplary one and the elements can be implemented in other manners and geometries. For example, the end portion of the needle 20 may be formed with another shape (e.g. convexly tapered), the needle seat 26 and the nozzle 5 can be formed two by separate elements, and the like.

[0147] FIG. 5 shows an ejector 100 according to a second embodiment of the present invention. The ejector 100 is in general of the same structure than the ejector 1. Hence, only the relevant differences from the ejector 1 are explained in the following and the same reference signs are used for corresponding elements.

[0148] The ejector 100 shown in FIG. 5 differs from the ejector 1 of FIGS. 1 in that the needle 20 has a modified needle tip 121. FIG. 6 is a magnified section of FIG. 5 around the needle tip 121.

[0149] In this embodiment, the needle tip 121 includes an intermediate cylindrical portion 123. In more detail, the needle tip 121 comprises a first tapered portion 122, the cylindrical intermediate portion 123, and a second tapered portion 124. The first tapered portion 122 constitutes a downstreamside end of the needle tip 121 (in the longitudinal direction L). The second tapered portion 124 is adjacent to the needle stem 25. Seen along the longitudinal direction L, the intermediate portion 123 is arranged between the first tapered portion 122 and the second tapered portion 124. The needle stem 25 and the needle tip 121 may be formed integrally. Due to the cylindrical intermediate portion 123, a substantial fluid flow out of the nozzle 5 occurs only if the needle 20 is moved away from abutment with the needle seat 26 be at least a certain distance, the latter being larger than zero. In other words, there is a dead zone, in which no or at least no substantial fluid flow through the nozzle 5 occurs when the needle 20 is not in abutment with the needle seat 26 but displaced away by less than the certain distance. This reduces a sensitivity of the ejector 100 for pressure and/or flow pulsations of the fluid at the primary inlet 2.

[0150] FIG. 5 also shows a spring-elastic member 81 biasing the check member 80.

[0151] While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.