Flow control valve, for example expansion valve for a refrigeration system

Abstract

Flow control valve of pressure-balanced piston type with mechanical fail-save function, equalization passage, and equalization pilot valve The present invention relates to a flow control valve (1; 100), for example an expansion valve for a refrigeration system, of pressure-balanced piston type and with a mechanical fail-safe functionality The valve (1; 100) comprises a valve body (10), a piston (60), and a valve drive (30) for controlling fluid flow from a fluid inlet (11) to a fluid outlet (15) through a valve seat (13) by displacing the piston (60) with regard to the valve seat (13). The piston (60) protrudes with a drive-side end portion (61) into a balancing chamber (20) and includes an equalization passage (70) with a first flow resistance. In order to provide the valve (1; 100) cost-efficiently with a reliable fail-safe functionality, it comprises a fluid bleed (25) from a inlet pressure chamber (12) and / or the fluid inlet (11) to the balancing chamber (20), wherein the fluid bleed (25) is separate from the equalization passage (70) and has a second flow resistance that is larger than the first flow resistance, and an equalization pilot valve (80) for opening and closing the equalization passage (70).

Description

[0001] FLOW CONTROL VALVE, FOR EXAMPLE EXPANSION VALVE FOR A REFRIGERATION SYSTEM

[0002] The present invention relates to a flow control valve, for example an expansion valve for a refrigeration system, of pressure-balanced piston type and with a mechanical fail-safe functionality.

[0003] A cooling system may include an evaporator, a condenser, an expansion valve, and a compressor for circulating a refrigerant. The expansion valve can be such a flow control valve and may be actuated by a motor.

[0004] In order to need a less powerful motor, the valve can be of pressure-balanced piston type. An example is shown in US 9,494,253 B2. It includes a piston for engaging a valve seat. The piston is axially displaceable along a longitudinal direction by the motor. A balancing chamber is formed at a side of the piston opposite from the valve seat. An equalization passage is formed between an area downstream of the valve seat and the balancing chamber. The equalization passage allows adaption of a balancing pressure in the balancing chamber to a pressure downstream of the valve seat. Axial forces applied onto the piston by the balancing chamber and the pressure below the valve seat can partly compensate.

[0005] If a power supply for providing electrical energy fails ("power-failure"), the motor is not powered any more. The motor and the valve can remain in a position where the valve is open. The refrigerant can condense as fluid in the cold evaporator. When the external power supply starts up again, there is a high risk that the compressor sucks in fluid and becomes damaged.

[0006] According to an approach to avoid such problems, a controller for the motor can include a power accumulator. The power accumulator is used to close the valve if the external power supply fails. However, this solution is expensive. Further, it can be necessary to replace the power accumulator periodically. This leads to additional maintenance efforts and expenses.

[0007] A flow control valve of pressure-balanced piston type with a mechanical fail-salve function is disclosed in US 6,997,430 B2. A pressure spring presses the piston towards a valve seat. In order to keep the valve closed reliably in the case of power-failure, the spring must be strong. It must apply enough force to keep the piston in abutment with the valve seat even if pressure fluctuation occurs. The motor must be relatively strong and requires high power for opening the valve.

[0008] Another expansion valve is known from US 4,911 ,401 A. It utilizes a piston assembly which is balanced to a high pressure by a bleed system through a piston. A return spring urges the piston assembly into engagement with a push rod assembly.

[0009] The object underlying the present invention to provide a cost-efficient flow control valve with a reliable fail-safe functionality.

[0010] This problem is solved by a flow control valve, for example an expansion calve, especially for a refrigeration system with the features according to claim 1 .

[0011] The flow control valve is of pressure-balanced piston type and has a mechanical fail-safe functionality. The valve comprises: a valve body with a fluid inlet, an inlet pressure chamber which is fluidly connected with the fluid inlet, a fluid outlet, a valve seat arranged between the inlet pressure chamber and the fluid outlet, and a balancing chamber; a piston; and a valve drive for controlling fluid flow from the fluid inlet to the fluid outlet through the valve seat by displacing the piston with regard to the valve seat along an axial direction, wherein the valve drive comprises a motor and a drive member, which is drivable by the motor, for axially entraining the piston, wherein the piston protrudes with a drive-side end portion into the balancing chamber and includes an equalization passage with a first flow resistance from the drive-side end portion to an equalization opening that is in fluid connection with the fluid outlet, wherein the valve comprises a fluid bleed from the inlet pressure chamber and / or the fluid inlet to the balancing chamber, wherein the fluid bleed is separate from the equalization passage and has a second flow resistance that is larger than the first flow resistance, and wherein the valve comprises an equalization pilot valve for opening and closing the equalization passage.

[0012] The present invention allows to take advantage of several synergistic effects. The mechanical fail-safe functionality ensures high safety.

[0013] When the equalization pilot valve is open, a "balancing" functionality is enabled. A pressure in the balancing chamber (a balancing pressure) at least substantially adapts to a pressure downstream of the valve seat. The second flow resistance being larger than the first flow resistance ensures that the balancing pressure is less affected by the fluid bleed than by the equalization passage when the equalization pilot valve is open. The valve drive needs to provide only low forces for opening and closing the valve. Further, due to the equalization passage, the valve is less influenced from pulsations of a fluid flow through the valve.

[0014] In the present invention, the equalization passage is closable. The "balancing" functionality can be disabled by means of the equalization pilot valve whenever it is not needed or even disadvantageous. The fluid bleed then increases the balancing pressure. In a conventional valve pressure-balanced piston type without the equalization pilot valve, the balancing pressure is always substantially the same as an outlet pressure, in particular also when the valve is closed. A total axial force on the piston (towards the valve seat) applied by the fluid results from a pressure difference between an inlet pressure and an outlet pressure times a (typically ring- shaped) contact area of the valve seat and the piston when the valve is closed. In this regard, only this small contact area contributes to the total axial force. Hence, this total axial force keeping the valve closed is rather small and the conventional valve is prone to unintentional opening due to pressure fluctuations and valve fluttering. With the present invention, the equalization pilot valve can be closed when the flow control valve is closed, for example. The balancing chamber is then pressurized driven by the inlet pressure via the fluid bleed. In this case, the total axial force on the piston towards the valve seat applied by the fluid results from the pressure difference (between the inlet pressure and the outlet pressure) times a sum of the contact area of the valve seat and the piston and an area surrounded by said contact area. The latter surrounded area is typically much larger than the contact area. The valve according to the present invention is held in the desired state much more firmly and much more reliable by increasing the balancing pressure via the bleed if the equalization pilot valve is closed. This improves the fail-safe functionality. Any means for urging the valve into the desired state (e.g. closed state) in order to providing the fail-safe functionality need to be less strong. They can be smaller, lighter, and less expensive. As the fail-safe functionality needs less strong means, less driving force is required for opening and closing the valve (when the equalization pilot valve is open). The valve drive can be less powerful, smaller, lighter, and less expensive.

[0015] Summed up, the present invention allows for cost-efficient flow control valve with a reliable fail-safe functionality. The mechanical fail-safe functionality may be configured to automatically close the valve (normally closed valve), to automatically open the valve (normally open valve), or to automatically bring the valve into another predetermined posi- tion / state (e.g. to a predetermined opening degree between closed state and a fully open state) in the case of power-failure.

[0016] According to one aspect, the flow control valve allows for so-called forced opening by the motor in case there is no pressure difference present. The movement of the piston is driven by the motor but not by relying on a pressure difference.

[0017] In one embodiment, the motor is an electric motor. Especially, the motor may be a stepper motor. The stepper motor allows for precise adjustment of an opening degree of the valve. Additionally or alternatively, the valve drive can include a conversion mechanism for converting rotational movements provided by the motor (e.g. the stepper motor) into axial movements of the piston. This allows using rotational motor types.

[0018] Other types of electrical motors can be used as well. The electric motor must be configured to stand-still electrically in several positions (e.g. in any position between the fully open state and the closed state of the valve). Optionally, the valve drive, for example the electric motor, can include a position sensor, e.g. for detecting a position of the piston.

[0019] The (stepper) motor may be of a type with a low detent torque. Especially, the motor can be a variable reluctance stepper motor. The variable reluctance stepper motor will not generate any detent torque (at least no significant detent torque) when it is not powered. There are no permanent magnets in the rotor that generate currents in the stator when the rotor is turned by an external force, especially when a resilient returner element (see below) backwinds the valve drive. In other words, the motor does not provide resistance against backwinding caused by permanent magnets. Thus, a weaker resilient returner element can be used. It can be less-expensive, smaller, and lighter. If the resilient returner element is weaker, a less powerful motor is sufficient to overcome the force of the resilient returner element (in normal operation), e.g. for opening the valve. The motor can be less-expensive, smaller, and lighter as well and might be more efficient.

[0020] It is also possible to use stepper motor types with rotors including permanent magnets. For example, the motor may be a hybrid stepper motor. There is a balance between the detent torque generated of by a backwinding speed (and corresponding rotational speed of the rotor) applied by the resilient returner element, an electrical resistance in a motor controller, and a maximum allowed time for bringing the valve in a predetermined state by the mechanical fail-safe functionality in case of power-failure.

[0021] According to one aspect, at least the rotor of the motor (e.g. the stepper motor) is housed in a motor chamber that is in fluid connection with the balancing pressure chamber. This increases the efficiency of the valve.

[0022] The stator may be arranged in the motor chamber. This further increases the efficiency and may facilitate manufacturing. Alternatively, the stator is external. The stator is not exposed to the fluid, e.g. the refrigerant, in operation. A wall of the motor chamber, e.g. a thin-walled tube, separates the external stator from the motor chamber and hence from the fluid.

[0023] Any elements exposed to the fluid should be resistant to the fluid.

[0024] In one embodiment, the drive member and the piston form the equalization pilot valve and mechanical coupling between the drive member and the piston allows limited relative axial displacement of the drive member relative to the piston for opening and closing the equalization pilot valve. Especially, the equalization pilot valve may be openable and closable by axial displacement of the drive member relative to the piston. As s soon as the limited relative axial displacement is used up, further axial movement of the drive member relative to the piston automatically (in the same direction) entrains the piston.

[0025] The mechanical coupling between the drive member may include a hook arrangement between the drive member and the piston.

[0026] In one embodiment, the valve comprises, at a middle portion of the piston between the inlet pressure chamber and the balancing chamber, a labyrinth seal between the piston and the valve body. A balanced piston is normally sealed with lib-seals or piston rings. This results in friction depending on differential pressures and swelling of the polymer as well as a risk for stick-slip behavior, and the like. The labyrinth seal provides very low friction. This contributes, in a synergistic manner, to the advantage that the resilient returner element can be less strong and that less motor force is needed for opening and closing the valve.

[0027] The labyrinth seal may form part of the fluid bleed channel. The labyrinth seal gives some leakage if there is a pressure difference along it. This is typically seen as disadvantageous. The present invention uses this leakage, in a synergistic beneficial manner, to constitute or at least form part of the fluid bleed. In particular, the labyrinth seal may (at least substantially) determine the second flow resistance.

[0028] According to one aspect, the valve can comprise a resilient returner element for automatically bringing the piston to a predetermined position when the motor is not powered. For example, the resilient returner element may be compressed when the piston is displaced away from the predetermined position. The compression may increase with increased displacement of the piston away from the predetermined position. The resilient returner element may be preloaded in compression when the piston is in the predetermined position. For example, the predetermined position may correspond to the closed state of the valve. The predetermined position is an abutment position of the piston in which the piston abuts on and seals against the valve seat. A resilient force provided by the resilient returner element is configured (e.g. high enough) to bring the piston into the predetermined position in the case of power-failure. Vice versa, the motor must have sufficient power to overcome, e.g. during opening the valve, friction regarding movement of the piston, axial forces applied onto the piston by the fluid, and the force necessary to compress the resilient returner element for opening the valve from the closed state. The resilient element may comprise a spring-elastic element, for example an axial spring (e.g. a coil-type spring) and / or a torsion spring (e.g. a flat-type torsion spring or a round spiral-type torsion spring).

[0029] The resilient returner element may act on the valve drive. For example, the resilient returner element may act on any one of the following: the rotor, a motor shaft, the spindle, and the drive member. At least one end of the resilient returner element may be rotationally and / or axially fixed with regard to the valve body.

[0030] In one embodiment, the drive member is threadedly engaged with and drivable by a spindle, which is rotatable by the motor. The drive member may be a nut member.

[0031] A pitch of the threaded engagement between the drive member and the spindle may be 3 mm per revolution at the minimum. The high pitch gives a large axial movement of the driver member per revolution of the spindle. This ensures that only a low force is required to rotate the spindle backwards if the motor force disappears (in the case of power-failure). The spindle may comprise a thread with at least one thread lead for threadedly engaging the drive member. Especially, the spindle's thread can comprise several thread leads (i.e. be a "multi-start thread").

[0032] The drive member may be prevented from rotation relative to the valve body, e.g. by a splined engagement with the valve body. The drive member may comprise anti-rotation wings that are guided in axial slots in the valve body.

[0033] According to one aspect, a first end of the resilient returner element may be rotationally coupled (e.g. directly) to the spindle. The first end is prevented from rotation with respect to the spindle. A second end of the resilient returner element may be rotationally coupled to the valve body, e.g. directly to the valve body and / or via the drive member.

[0034] According to another aspect, a first end of the resilient returner element may axially abut (e.g. directly) on the drive member along the axial direction. A second end of the resilient returner element may axially abut (directly) on the valve body.

[0035] In one embodiment, the resilient returner element is a torsion spring and acts directly on the spindle. This ensures particularly low friction and easy return of the valve to the predetermined state.

[0036] According to one aspect, the equalization pilot valve opens before the piston is displaced out of the predetermined position, e.g. before the piston lifts off from the valve seat for opening the valve. The balancing functionality is enabled before the piston starts to move axially. Only a low valve drive force (motor force) is necessary to open the valve.

[0037] According to one aspect, the valve is configured such that (in operation) the equalization pilot valve is automatically opened when the motor is powered to drive the piston away from its predetermined position. The equalization pilot valve may be opened by initial (e.g. axial) movement of the drive member relative to the piston when the motor is powered to drive the piston away from its predetermined position. Especially, the equalization pilot valve may be opened by the initial (e.g. axial) movement of the drive member relative to the piston before the drive member entrains the piston when the motor is powered to drive the piston away from its predetermined position.

[0038] In one embodiment, the piston comprises, at an outlet-side end in the axial direction opposite to the drive-side end portion, a protruding portion having an outer circumference corresponding to an inner circumference of the valve seat. The protruding portion may have an (at least substantially) cylindrical basic shape and / or conical basic shape.

[0039] Further, the protruding portion can have at least one fluted part, wherein a flow passage from the inlet pressure chamber to the fluid outlet through the valve seat is defined between the at least one fluted part and the valve seat when the piston is lifted off from the valve seat. The size of the flow passages may increase with increasing displacement of the piston away from its abutment position.

[0040] According to one aspect, the piston may include a supplementary equalization passage for establishing a fluid connection between the inlet pressure chamber and the equalization passage when the piston is lifted off from the valve seat. The supplementary equalization passage may include a channel opening arranged in the protruding portion of the piston, preferably outside from any one of the fluted parts. This ensures that the valve drive force (especially the motor force) for displacing the piston is relatively uniform over a stroke of the piston.

[0041] In one embodiment, an effective flow cross-section of the supplementary equalization passage gradually increases with increasing axial displacement of the piston towards the drive-end side over a predetermined movement range of the piston along the axial direction. This feature ensures that the pressure in the equalization passage and hence in the balancing chamber is increased faster during opening, namely faster than a pressure at the equalization opening, but in a smooth manner. This helps to ensure that an even more uniform valve drive force (especially the motor force) for displacing the piston over the predetermined movement range of the piston is required. Said groove may be arranged outside from any of the fluted parts.

[0042] The supplementary equalization passage may have a groove formed in a region of the outer circumference of the protruding portion comprising the channel opening, wherein the groove extends (substantially) along the axial direction and is tapered with increasing cross-sectional diameter towards the outlet-side. This embodiment is comparatively easy to manufacture but nevertheless has the desired properties.

[0043] In particular, the groove may be tapered with increasing depth toward the outletside.

[0044] The outer opening of the supplementary equalization passage may be arranged at an outlet-side end portion of the groove.

[0045] In one embodiment, the valve drive includes a gear box between the motor and the drive member. Especially, the gear box can be arranged between the motor and the spindle.

[0046] A gear ratio (revolution spindle:revolution motor) can be lower than 1 :1 , e.g. in the range from 1 :1 ,5 to 1 :4, for example 1 :2. If the resilient returner element acts on the element downstream of the gear box in the valve drive, the motor needs to be less powerful in order to overcome the resilient force of the resilient returner element. The resilient force of the resilient returner element is sufficient to overcome an overall resistance of the valve drive against return to the predetermined position.

[0047] In another embodiment, the spindle is directly rotationally coupled to a motor shaft of the motor. This reduces complexity and facilitates production.

[0048] The spindle, the gear box, and / or the rotor may be supported by guide-bearing means. The guide-bearing means may be configured to absorb axial loads.

[0049] According to one aspect, the valve is configured such that (in operation) the equalization pilot valve automatically closes the equalization passage at least when

[0050] - the valve is in the predetermined state (e.g. when the piston is not in the predetermined position) and, at the same time,

[0051] - the motor is not powered.

[0052] The valve may be configured such that (in operation) the increased balancing pressure when the equalization pilot valve is closed assists to maintain the valve in the predetermined state (e.g. to keep the piston in the predetermined position) when the motor is not powered. It may be configured that a motor force needed to displace the piston along the axial direction is decreased due to a reduction of the balancing pressure when the equalization pilot valve is opened.

[0053] At least a part of the equalization pilot valve may be mechanically coupled, e.g. via the driver member and / or the spindle, to the resilient returner element. The valve may be configured such that the resilient returner element urges the equalization pilot valve to be closed when the motor is not powered.

[0054] The problem is further solved by a refrigeration system including the flow control valve according to the present invention. The embodiments, modifications, and advantages described regarding the flow control valve may apply accordingly and vice versa.

[0055] The refrigeration system may be a cooling system or a heat pump. The refrigeration system may comprise at least one of, several, or all of the following: an evaporator, a condenser, an expansion device (e.g. including the disclosed valve), and a compressor.

[0056] The flow control valve according to the present invention may be used as the expansion device.

[0057] Preferred embodiments of the invention will now be described with reference to the drawings, in which:

[0058] Fig. 1 shows a longitudinal cross-section of a first embodiment of a flow control valve according to the present invention in a closed state;

[0059] Fig. 2 shows a longitudinal cross-section of the valve of Fig. 1 in a fully open state;

[0060] Fig. 3 shows a magnified longitudinal cross-section area of the valve of Figs. 1 and 2 around a balancing chamber in the closed state (as in Fig. 1 );

[0061] Fig. 4 shows the area of Fig. 3 at the end of a first stage of opening the valve;

[0062] Fig. 5 shows the area of Figs. 3 and 4 in the fully open state of the valve;

[0063] Fig. 6 shows a magnified longitudinal cross-section area around a valve seat in the closed state (as in Fig. 1 );

[0064] Fig. 7 shows the area of Fig. 6 in the fully open state of the valve;

[0065] Fig. 8 shows an even more magnified section of the valve of Figs. 1 and 2 around the valve seat in a transition between the closed state and the fully open state; Fig. 9 shows a relation between an axial displacement of a piston and an effective flow cross section of a supplementary equalization passage of the valve of Figs. 1 and 2;

[0066] Fig. 10 shows a perspective view on a drive-side part of the piston of the valve of Figs. 1 and 2;

[0067] Fig. 11 shows a longitudinal cross-section of a second embodiment of a flow control valve according to the present invention in a closed state;

[0068] Fig. 12 shows a lateral view on a lower part of the piston of the valves in Figs. 1 , 2, and 11 ;

[0069] Fig. 13 shows a longitudinal cross-section of the lower part of the piston;

[0070] Fig. 14 shows a perspective view on a drive member of the valve of Fig. 11 ;

[0071] Fig. 15 shows a sectional view of the drive member;

[0072] Fig. 16 shows a sectional view of an upper part of the valve of Fig. 11 with a motor and a gearbox;

[0073] Fig. 17 shows a round spiral-type torsion spring used as a resilient returner element in the valve of Fig. 11 ; and

[0074] Fig. 18 shows an alternative flat-type torsion spring.

[0075] Fig. 19 shows a longitudinal cross-section of a third embodiment of a flow control valve according to the present invention in a predetermined state with a predetermined opening degree between a closed state and a fully open state;

[0076] Fig. 20 shows an enlarged section of the valve of Fig. 19 around a conversion mechanism when the valve is in a fully open state, i.e. when a piston is in a fully retracted position; and

[0077] Fig. 21 shows the enlarged section of the valve of Fig. 19 around the conversion mechanism when the piston abuts a valve seat.

[0078] Figs. 1 and 2 show a first embodiment of a flow control valve 1 according to the present invention. Fig. 1 shows the valve 1 is in a closed state. Fig. 2 shows it in a fully open state. The valve 1 may be an expansion valve for a refrigeration system.

[0079] The valve 1 comprises a valve body 10 with a fluid inlet 11 . A fluid, for example a refrigerant of the refrigeration system, can flow into the valve body 10 through the fluid inlet 11 . The valve body 10 may include a fluid inlet port 11 a forming the fluid inlet 11 . Further, the valve body 10 has a fluid outlet 15. The fluid can flow out of the valve body 10 through the fluid outlet 15. The valve body 10 may comprise a fluid outlet port 15a forming the fluid outlet 15 (for the regulated flow). A flow direction of the fluid in operation may be defined from the fluid inlet 11 to the fluid outlet 15. The valve body 10 may comprise an inlet pressure chamber 12 that is in (direct) fluid connection with the fluid inlet 11 and / or an outlet pressure chamber 14 that is in (direct) fluid connection with the fluid outlet 15.

[0080] The valve body 10 comprises a valve seat 13 that is arranged between the fluid inlet 11 and the fluid outlet 15 along the flow direction. The valve seat 13 may be arranged between the inlet pressure chamber 12 and the fluid outlet 15, especially between the inlet pressure chamber 12 and the outlet pressure chamber 14.

[0081] The valve body 10 may include several parts. In this example, it includes a lower housing section 2, a seat insert 3, a guiding insert 4, a middle housing section 5, and a motor housing section 6. The seat insert 3, the guiding insert 4, the middle housing section 5, and the motor housing section 6 are fixed relative to the lower housing section 2. They can be fixed releasably relative to the lower housing section 2 for allowing maintenance. For example, the seat insert 3 may be fixed to the guiding insert 4, the motor housing section 6 may be fixed to the middle housing section 5, and the middle housing section 5 may be releasably fixed to the lower housing section 2, thereby holding the guiding section 4 and the seat insert 3 in position in the lower housing section 2. The fluid inlet port 11a as well as the fluid outlet port 15a are formed in the lower housing section 2. The seat insert 3 is inserted into the lower housing section 2 and includes the valve seat 13. The valve seat 13 is formed at a downstream-side wall 3a of the seat insert 3. The downstream-side wall 3a separates the outlet pressure chamber 14 and the inlet pressure chamber 12. The valve body 10, here the seat insert 3, may include a fluid passage 13a (see reference sign in Fig. 2) from the valve seat 13 (at the side with the inlet pressure chamber 12) to the outlet pressure chamber 14. In this example, the fluid passage 13a has a conical shape. A sealing means may be provided between the seat insert 3 (especially the down- stream-side wall 3a) and the lower housing section 2. The valve seat 13 may project into the inlet pressure chamber 12 in an axial direction L. The valve seat 13 and / or the fluid passage 13a may have a shape rotational-symmetric with regard to a central axis C of the piston 60 (see Fig. 8). The central axis C is parallel to the axial direction L. In this embodiment, the valve seat 13 is formed on a projection with a cone-shaped outer circumferential surface. The projection can have a rotational-symmetric shape with regard to the central axis C.

[0082] The valve 1 comprises a piston 60, which is movable along the axial direction L. When the valve 1 is closed (in the closed state), the piston 60 abuts the valve seat 13 and seals against the valve seat 13. This situation is shown in Figs. 1 and 6. The piston 60 is in an "abutment position". Hence, (direct) fluid flow from the inlet pressure chamber 12 towards the outlet 15 (i.e. direct fluid from the inlet pressure chamber 12 to the outlet pressure chamber 14) is prevented. Contrary to the fully open state shown in Figs. 2 and 7, there is no flow passage 67 between the piston 60 and the valve seat 13.

[0083] When the valve 1 is open, the piston 60 is lifted off from the valve seat 13. In other words, the piston 60 is moved out of abutment with the valve seat 13. Figs. 2, 5, and 7 relate to a situation where the valve 1 is in its fully open state. The piston 60 is displaced away from its abutment position along the axial direction L by a maximum stroke MS (see Fig. 5 in comparison to Fig. 3). The piston 60 is in a "fully retracted" position. The maximum stroke MS of the piston 60 correspond to its displacement between its abutment position and its fully retracted position.

[0084] The valve 1 comprises a valve drive 30 for moving the piston 60 along the axial direction L.

[0085] The valve drive 30 includes a motor 31. In the valve 1 shown in Figs. 1 and 2, the motor 31 is a stepper motor, more specifically a variable reluctance stepper motor with a soft iron motor. The motor 31 has a motor shaft 35, a rotor 33 that is at least rotationally fixed to the motor shaft 35, and a stator 34. The rotor 33 (with the motor shaft 35) is accommodated within a motor chamber 32. The motor chamber 32 is in fluid connection with a balancing chamber 20. The stator 34 includes coils.

[0086] In the embodiment shown in Figs. 1 and 2, the stator 34 is arranged outside the motor chamber 32, circumferentially around the rotor 33. The valve body 10 (namely the motor housing section 6) separates the stator 34 from the rotor 33. The valve body 10 separates the stator 34 from the fluid. The stator 34 is arranged at an outer side of the valve body 10. This approach is beneficial in cases where the fluid, e.g. the refrigerant, is inflammable, explosive, and / or corrosive. For ex- ample, the embodiment shown in Figs. 1 and 2 is particularly suitable for refrigeration systems where the refrigerant includes ammonia (NH3).

[0087] The valve drive 30 further comprises a spindle 40 coupled to the motor 31 . In the embodiment shown in Figs. 1 and 2, the spindle 40 is directly rotationally coupled to the motor shaft 35.

[0088] A conversion mechanism 45 of the valve drive 30 converts rotational movements of the spindle 40 (with respect to the valve body 10) into axial movements (with respect to the valve body 10). The spindle 40 has a multi-start outer thread 41 threadedly engaged with an inner thread 51 of a drive member 50. The drive member 50 is prevented from rotation with respect to the valve body 10 by an anti-rotation mechanism 49.

[0089] The piston 60 is at least axially coupled to the drive member 50, in this embodiment by a mechanical coupling 55. If the drive member 50 is axially displaced by the motor 31 (via rotation of the spindle 40), the drive member 50 entrains the piston 60, at least when the relative axial displacement of the drive member 50 with regard to the piston 60 exceeds a limited relative axial movement. Hence, the piston 60 is axially displaceable by the motor 31 via rotation of the spindle 40 and corresponding axial displacement of the drive member 50.

[0090] The mechanical coupling 55 between the drive member 50 and the piston 60 allows for the limited relative axial displacement of the drive member 50 relative to the piston 60. The limited relative axial displacement may be smaller than the maximum stroke MS. For example, it might correspond to up to 10 % of the maximum stroke MS.

[0091] The mechanical coupling 55 in the valve 1 according to the first embodiment (see Figs. 1 and 2) may be the same as in the valve 100 according to the second embodiment (see Fig. 11 ). The mechanical coupling 55 is hence described in more detail also considering Figs. 10, 14 and 15. It includes a hook structure 55 at the drive member 50, 150 engaging a first flange 54 formed at a drive-side end portion 61 of the piston 60. The hook structure 54 includes a receiving recess 54a (see Figs. 14 and 15) for receiving the tip 61 a and the first flange 57. The receiving recess 54a is limited by a shoulder 54b. If a proximal displacement of the drive member 50, 150 relative to the piston 60 has reached the end of the limited relative axial movement, the shoulder 54b engages the first flange 57. The piston 60 follows any further proximal movement of the drive member 50 relative to the valve body 10. "Proximal" may mean in the axial direction L away from abutment on the valve seat 13 (upwards in Figs. 1 to 8 and 11 to 13). "Distal" may mean in the axial direction L towards abutment on the valve seat 13 (downwards in Figs. 1 to 8 and 11 to 13).

[0092] The drive-side end portion 61 may further comprise a second flange 59, which is arranged distally from the first flange 57, and a groove 58 formed between the first flange 57 and the second flange 59 (see Fig. 10). The groove 58 is inserted into a slit within the shoulder 54b (see Figs. 14 and 15). A width of the groove 58 in the axial direction L may be larger than a sum of the limited relative axial movement and a wall thickness of the shoulder 54b along the axial direction L. This ensures tight sealing of the seal member 53 against the tip 61a when the drive member 50 is forced distally against the piston 60, e.g. due to the motor 31 , 131 and / or the returner element 43, 143, 243.

[0093] The valve 1 is of pressure-balanced piston type. It includes a balancing chamber 20. The drive-side end 61 of the piston 60 along the axial direction L protrudes into the balancing chamber 20. The piston 60 extends along the axial direction L. An end of the piston 60 along the axial direction L opposite to the balancing chamber 20 may be referred to as outlet-side end of the piston 60. A protruding portion 64 is formed at the outlet-side end. A least when the valve 1 is closed, the outlet-side end of the piston 60 protrudes through the valve seat 13. The protruding portion 64 then protrudes through the valve seat 13 into the fluid passage 13a (see Fig. 6).

[0094] A diameter where the piston 60 contacts the valve seat 13 (a nozzle sealing diameter) and an effective diameter of the piston 60 at the balancing chamber are at least substantially the same, i.e. almost the same (difference of the diameters might be less than 10 %, for example) or the same. According to one aspect, the nozzle sealing diameter is a larger than the effective diameter of the piston 60 at the balancing chamber 20, e.g. by at least 1 %, maybe by 10 % at the maximum. This helps for safe abutment of the piston 60 onto the valve seat 13 if the valve 1 is closed.

[0095] An equalization passage 70 is formed in the piston 60. It extends within the piston 60 along the axial direction L from the drive-side end 61 to the protruding portion 64. It has a balance chamber opening 71 at the drive-side end 61 and an equalization opening 72 at the protruding portion 64. In more detail, the balance chamber opening 71 is formed in a drive-side tip 61a of the piston 60.

[0096] At least when the valve 1 is closed, maybe at least when the piston 60 is not moved away from the abutment position by more than a third (in some embodiments: three quarters) of its maximum stroke MS, the equalization opening 72 is located downstream of the valve seat 13. The equalization opening 72 is always in fluid communication with the fluid outlet 15. If the valve 1 is closed, the equalization opening is subjected to an outlet pressure applied at the fluid outlet 15.

[0097] An equalization pilot valve 80 of the valve 1 is configured to open and close the equalization passage 70, i.e. to enable and disable direct fluid communication between the balancing chamber 20 and the equalization opening 72 (and hence "direct" pressure adaption between the balancing chamber 20 and the outlet 15 via the equalization passage 70).

[0098] The equalization pilot valve 80 is formed by the drive-end side portion 61 of the piston 60 and a piston-side end (in the axial direction L) of the drive member 50. In the valves 1 and 100 according to the exemplary embodiments, the drive member 50, 150 comprises a seal member 53 and the equalization pilot valve 80 is formed between the drive-end side tip 61 a of the piston 60 and a sealing member 53 that faces the piston 60. The seal member 53 may be arranged in seal mount 53a and secured by a retainer ring 53c engaging an annular groove 53b formed in the seal mount 53a.

[0099] In the closed state of the valve 1 (as shown in Figs. 1 and 3), the drive member 50 abuts distally (i.e. in the axial direction L towards the valve seat 13) on the piston 60 and thereby closes the equalization passage 70. In particular, the seal member 53 abuts on the tip 61 a of the piston 60, seals against the tip 61 a, and closes the balancing chamber opening 71 .

[0100] The piston 60 includes a main rod 60a and a lower part 60b. The lower part 60b is fixed to the main rod 60a, e.g. by a threaded engagement 60c. The lower part 60bcomprises the outlet-side end with the protruding portion 64. The main rod 60a comprises the drive-side end 61 protruding into the balance pressure chamber 20. The main rod 60a also includes a middle portion 62 of the piston 60. At least a part of the middle portion 62 is axially movably guided in a rod guide channel 3b of the valve body 10 (between the balancing chamber 20 and the inlet pressure chamber 12). Here, the rod guide channel 3b is formed in the guiding insert 3.

[0101] The middle portion 62, which is guided in the rod guide channel 3b, might have a diameter (referred to as piston diameter DP, see Fig. 5) in the range from 3 mm to 12 mm, e.g. 6 mm. Depending on the required valve size, the diameter could be larger or smaller. An effective area of the piston 60 at the balancing chamber 20 is an area with which the balancing pressure can be multiplied in order to calculate a distal force applied to the piston 60 resulting from the balancing pressure (maybe if the equalization pilot valve 80 is closed or if the equalization pilot valve 80 is open but the area of the balance chamber opening 71 is neglected). In this embodiment, the effective area (also referred to as balancing area) can be obtained from the piston diameter DP easily. The balancing pressure also acts on the drive member 50 and in the motor chamber 32 such that pats of the valve drive 30 (especially the motor shaft 35, the spindle 40, and the drive member 50) may contribute to applying said "distal force applied to the piston 60 resulting from the balancing pressure" (also referred to as balancing force) onto the piston 60, at least when the equalization pilot valve 80 is closed.

[0102] The lower portion 60b of the piston 60 can be seen best in Figs. 12 and 13. Fig. 13 is a cross-sectional view of the lower portion 60b in a plane spanned by the central axis C and a transversal axis CT in Fig. 12. It includes a flange section 90, in which an outer diameter is larger than the piston diameter DP (see Fig. 5). The flange section 90 includes a seal mount 92. A seal member 94 is accommodated in the seal mount 92 and secured therein by a retainer ring 95 engaging an inward flange 91 at an outlet-side of the flange seal mount 92. An outlet-side of the seal member 94 abuts the valve seat 13 when the valve 1 is closed. This prevents fluid flow from the inlet pressure chamber 12 to the fluid passage 13a. A fluid passage 93 provides fluid communication between an interior of the seal mount 92 and the inlet pressure chamber 12.

[0103] An opening area of the valve seat 13 may correspond to the effective area of the piston 60. An inner diameter of the valve seat 13 may correspond to the piston diameter DP.

[0104] A sealing area at the valve seat 13 is delimited by an outer circumference of the valve seat 13, in this embodiment by a nozzle sealing diameter DS of the valve seat 13. The sealing area includes a contact area of the valve seat 13 and the piston 60 (especially the seal member 94) when the valve is closed, and the area surrounded by said contact area. In this example, the sealing area is larger than the balancing area, e.g. by 2 % to 20 %. For example, the piston diameter DP is 6 mm and the nozzle sealing diameter DS is 6,3 mm. Fig. 3 shows a magnified view on a section S1 of the valve 1 as indicated in Fig. 1 when the valve 1 is closed. The equalization pilot valve 80 is closed. Fig. 6 shows a magnified view on section S2 of the valve 1 as indicated in Fig. 1 . The piston 60 abuts on and seals against the valve seat 13.

[0105] The valve 1 comprises a fluid bleed 25 from the inlet pressure chamber 12 and / or the fluid inlet 11 to the pressure balancing chamber 20. As an example, the fluid bleed 25 is formed by a labyrinth seal 26 between the piston 60 and the rod guide channel 3b. An outer circumferential wall of the middle part 62 of the piston 60 is structured, e.g. with a helical groove (see outer thread 27 in Fig. 10) or a plurality of annular grooves, to form the labyrinth seal 26. A side wall of the rod guide channel 3b can be (at least substantially) smooth. In a modification, the side wall of the rod guide channel 3b is structured, e.g. with a helical groove or a plurality of annular grooves, to form the labyrinth seal 26. In this case, the outer circumferential wall of the middle part 60 can be (at least substantially) smooth, or structured as well. The labyrinth seal 26 may include at least 25 annular grooves or at least 50 helical turns.

[0106] The fluid bleed 25 allows restricted fluid flow from the inlet pressure chamber 12 to the balancing chamber 20. It has a first flow resistance (for such fluid flow). When the equalization pilot valve 80 is closed, a pressure in the balancing chamber 20 (a balancing pressure) increases towards an inlet pressure in the inlet pressure chamber 12. The resulting high balancing pressure causes the balancing force on the piston 60. This helps to keep the valve 1 closed reliably.

[0107] The protruding portion 64 has a cylindrical basic shape. However, it has at least one fluted part 66, preferably several fluted parts 66. In this embodiment, there are three fluted parts 66, which are arranged evenly around a circumferential direction. An outer circumferential wall of the protruding portion 64 is tapered in each fluted part 66 (e.g. inwardly, in other words along the flow direction towards the central axis C). The individual fluted part 66 may correspond to a recess that can be described by an intersection of an inclined plane with the basic cylindrical shape of the protruding portion 64. The fluted parts 66 and the resulting shape of the flow passages reduce a flow force impact on the piston 60 in all opening degrees.

[0108] When the piston 60 is lifting off from the valve seat 13, at each fluted part 66, a corresponding flow passage 67 from the inlet pressure chamber 12 to the fluid outlet 15 through the valve seat 13 forms, in particular between an inner circumferential wall of the valve seat 13 and the tapered section of the outer circumferential wall of the protruding portion 64 at the respective fluted part 66. Fig. 7 shows the section S2 in Fig. 2 when the valve 1 is fully open, wherein the piston 60 is in the fully retracted position. Fig. 8 shows a further magnified area around the valve seat where the piston 60 has lifted off from the valve seat 13 and is in a position between the abutment position and the fully retracted position.

[0109] For opening the valve 1 , at first the equalization pilot valve 80 is opened. As the mechanical coupling 55 between the drive member 50 and the piston 60 allows limited relative axial movement these elements, in an initial / first stage of opening the valve 1 , the piston 60 remains in its abutment position and only the drive member 50 moves proximally. Thereby, equalization pilot valve 80 is opened. The seal member 53 lifts off from the tip 61 a, thereby opening the balance chamber opening 71 . A direct fluid communication between the equalization passage 70 and the balancing chamber 20 is opened. As a pressure at the equalization opening 72 (downstream of the valve seat 13) correspond to an outlet pressure and is lower than the balancing pressure in this situation, fluid escapes from the balancing chamber 20 through the equalization passage 70 towards the outlet 15 (not passing directly between the piston 60 and the valve seat 13). The equalization passage 70 has a first flow resistance for the fluid. The first flow resistance is smaller than the second flow resistance, for example half of the second flow resistance at the maximum (maybe an eighth of the second flow resistance at the maximum). As the fluid can escape from the balancing chamber 20 through the equalization passage 70 more easily than being re-delivered into the balancing chamber 20 when the equalization pilot valve 80 is open, the balancing pressure decreases. Hence, the balancing force onto the piston 60 drops quite fast, e.g. to a minimum value.

[0110] As soon as the limited relative axial movement is used up (end reached), the mechanical coupling 55 entrains the piston 60 to follow further axial movement of the drive member 50 into the same direction (here: proximally). Fig. 4 shows an axial displacement of the drive member 50 relative to the piston 60 compared to Fig. 3. In Fig. 4, the limited relative axial movement is just used up and the shoulder 49b has just engages the first flange 57. The piston 60 is still in the same position than in Fig. 3, namely in its abutment position. Fig. 4 shows the end of the first stage of opening.

[0111] In a second stage of opening, the driving member 50 entrains the piston 60 via the mechanical coupling 55. From now on, the piston 60 follows any further proximal movement of the drive member 50 with a corresponding proximal displacement. Due to the pressure compensation by opening the equalizing pilot valve 80 in the first stage, an actuator force needed to start lifting off the piston 60 from the valve seat 13 may be determined by the contact area only (i.e. without the area surrounded the contact area) times the pressure difference between the inlet pressure and the outlet pressure plus friction. The total distal force applied by the fluid (i.e. the balancing force and other axial forces on the piston 60 resulting from the fluid) might act distally and have an absolute value of less than an upper limit in this situation. In this example, the upper limit is 50 N. The upper limit may depend on the valve size. The piston 60 starts to lift off from the valve seat 13 and to move away from the abutment position. The flow passages 67 between the valve seat 13 and fluted parts 66 of the protruding portion 64 open and become larger with increased proximal displacement of the piston 60 relative to the valve body 10. As long as the piston 60 is only slightly lifted away from the valve seat 13 (e.g. by 0,2 mm to 0,3 mm) in the second stage, an effect of the inlet pressure onto the protruding portion 64 is still small.

[0112] The more the piston 60 is displaced away from the abutment position, the larger is a "freed part" 64f of the protruding portion 64 (see Fig. 7). The freed part 64f is located upstream of the valve seat 13 in the inlet pressure chamber 12 and hence subject to the inlet pressure.

[0113] The freed portion 64f may include tapered parts narrowing towards the outletside, e.g. since the protruding portion 64 has the at least substantially conical shape and / or since the at least one fluted part 66 is tapered as in the present example. The inlet pressure applies, at the freed part 64f, an additional proximal force onto the piston 60 (in particular at freed sections of the fluted parts 66). This additional proximal force grows with increasing displacement of the piston 60 from the abutment position, maybe until the protruding portion 64 is completely retracted into the pressure inlet chamber 12.

[0114] The piston 60 includes a supplementary equalization passage 73 for establishing a fluid connection between the inlet pressure chamber 12 and the equalization passage 70 when the piston 60 is lifted off from the valve seat 13. The supplementary equalization passage 73 includes a channel opening 74 arranged in the protruding portion 64 of the piston 60 outside from any one of the fluted parts 66. An effective flow cross-section of the supplementary equalization passage 73 (i.e. from the inlet pressure chamber 12 to the equalization passage 70) gradually increases, e.g. linearly, with increasing proximal displacement of the piston 60, at least over a predetermined movement range MR of the piston 60.

[0115] In the exemplary embodiments, the supplementary equalization passage 73 has a groove 75 formed in a region of the outer circumference 65 of the protruding portion 64 comprising the channel opening 74. The groove 75 extends along the axial direction L and is tapered with increasing cross-sectional area towards the outlet-side. In the cross-sectional views of Figs. 1 , 2, 6, 7, 8, 11 , and 13, the groove 75 appears as triangular cut-out in the outer circumference of the protruding part 64. The groove 75 and the channel opening 74 are arranged completely outside of the fluted parts in section of the outer circumference 65 that has the basic conical shape.

[0116] Especially while the displacement of the piston 60 away from the abutment position is still small, the fluid flow between the valve seat 13 and the piston 60 is still small and a pressure around the equalization opening 72 is still comparatively low, e.g. (at least) substantially the initial outlet pressure.

[0117] Without the supplementary equalization passage 73, the (main) equalization passage 70 would still pull the balancing pressure completely down to said comparatively low pressure around the equalization opening 72. The balancing force on the piston 60 (resulting from the balancing pressure) would increase slower with increasing displacement of the piston 60 than the additional proximal force on the piston 60 resulting from the inlet pressure acting on the freed part 64f. This would give an undesired total proximal force on the piston 60 that could lead to unintentional proximal movement of the piston 60 and hence an unwanted jump of capacity of the valve 1 .

[0118] The additional supplementary equalization passage 73 ensures that the balancing pressure rises faster with increasing displacement of the piston 60 away from the abutment position. The supplementary equalization passage 73 is adapted such that a progression of the balancing force on the piston 60 is, at least over the movement range MR, better adapted to a progression of the additional proximal force onto the piston 60 applied by the inlet pressure onto the freed parts. This allows smooth opening and closing of the valve 1 with a less powerful motor 31 . As said additional proximal force is better compensated, a resilient returner element 43 can be less strong. Resulting forces for operating valve 1 can be reduced in all positions.

[0119] Fig. 9 shows an effective flow cross section of the supplementary equalization passage 73 (effective cross section, e.g. given in a unit of area, ordinate EFC) in relation to the axial displacement of the piston 60 away from abutment with the valve seat 13 (axial displacement in percent of the maximum Stroke MS, abscissa AD). When the axial displacement is zero, the effective flow cross section is practically zero (not shown). In the predetermined movement range MR, the effective flow cross section increases linearly with increasing axial displacement. In the predetermined movement range, an overlap of the groove 75 with the inlet pressure chamber 12 determines the effective flow cross section. Said overlap increases with increasing axial displacement. The pressure increase (to the equalization passage 70 and the balancing pressure) applied via the supplementary equalization passage 73 is in balance with equalization opening 72. The pressure increase of the balancing pressure may occur at the same rate as the inlet pressure affects the protruding part 64, e.g. the free part 64f thereof, in the proximal direction.

[0120] If the axial displacement reaches a certain threshold, the effective flow cross section becomes saturated. Then, the effective flow cross section of the supplementary equalization passage is determined by a flow cross-section of the opening 74 and / or a channel between the (main) equalization passage 70 and the opening 74. The pressure at equalization opening 72 might now not significantly increase any more when the piston 60 is moved farther towards the fully retracted position.

[0121] The valve 1 comprise a returner element 43 for automatically urging the valve 1 towards a predetermined state if the motor 31 is not powered. In other words, the valve 1 comprises a mechanical fail-safe functionality. In this example, the predetermined state is the closed state. The valve 1 is a normally closed valve. In a modification (not shown), the predetermined state is the fully open state. In that case, the resilient returner element 43 must be arranged such that its resilient force finally urges the piston 60 towards its fully retracted position.

[0122] In the valve 1 , the returner element 43 is arranged between a flange section 52 of the drive member 50 and valve body 10. A first end of the returner element 43 axially abuts on the flange section 52, a second end axially abuts on the valve body or an element that is at least axially fixed to the valve body. In this example, the second end abuts on a bearing plate 6a in the motor housing section 6 for bearing the motor shaft 35. The returner element 43 directly urges the drive member 50 distally, i.e. along the axial direction L towards the valve seat 13. As soon as a relative distal movement of the drive member 50 has used up the maximum relative axial movement between the drive member 50 and the piston 60, the drive member 50 (especially the seal member 53) directly abuts the piston 60 and thereby seals the equalization passage 70 as explained above. The piston 60 hence follows any further distal movement of the drive member 50 with respect to the valve body 10 (and hence towards the valve seat 13). Distal movements of the drive member 50 may be caused by the motor 31 and / or the returner element 43.

[0123] The returner element 43 may be a resilient element, e.g. a spring-elastic element. In valve 1 shown in Figs. 1 and 2, the returner element 43 is an axial spring, e.g. a cylindrical helical spring. A The valve 100 according to the second embodiment, which is shown in Fig. 11 , has basically the same structure and functionalities as the valve 1 according to the first embodiment. Identical reference signs are used for the same elements. In general, all explanations given with regard to the valve 1 and its components apply correspondingly to the valve 100 and its components and vice versa. Hence, only the differences are described in more detail.

[0124] There are three main differences of the valve 100 according to the second embodiment. All main differences concern the valve drive 130.

[0125] Firstly, in the valve 100, in addition to the rotor 133, the stator 134 of the motor 131 is also housed in the motor chamber 132. This makes the motor 131 more efficient and facilitates production. However, the valve 1 may be better suited for use with certain refrigerants as described above. The motor 131 may be stepper motor, e.g. a variable reluctance stepper motor also in this embodiment.

[0126] Secondly, the valve drive 130 of the valve 100 additionally comprises a gear box 136 between the motor 131. This allows using a less powerful and hence smaller, lighter, and more efficient motor 131.

[0127] In this example, the gear box 136 comprises several gear wheels 137a, 137b, 137c. Fig. 16 shows a motor section of the valve 100. A first gear wheel 136a is at least rotationally fixed to the motor shaft 135. A last gear wheel 136c is at least rotationally fixed, maybe rotationally and axially fixed, to the spindle 40. The last gear wheel 137c is supported by a ball bearing 138. The ball bearing 138 is fitted into the middle housing section 105. A gear ratio (revolution spindle 40 per revolution motor shaft 35) is higher than 1 : 1 , e.g. 1 :0.5 (two rotations of the motor shaft 135 result in one rotation of the spindle 40). This facilitates backwinding of the motor 31 by the resilient returner element 143, 243 in the case of power-failure. Thirdly, in the valve 100, a torsion spring directly engaging the spindle 40 is used as the resilient returner element 143, 243. A first end (an inner end) 243a of the torsion spring 143, 243 is directly fixed to the spindle 40. A second end (outer end) 243b, 243b of the torsion spring 143, 243 is directly secured to the valve body 10 and prevented from rotation with respect to the valve body 10. In this example, the second end 143b, 243b engages one of the slots 49b.

[0128] In Fig. 11 , the resilient returner element 143 is a round spiral-type torsion spring as shown in Fig. 17. Alternatively, a flat-type torsion spring as shown in Fig. 18 can be used as the resilient returner element 243.

[0129] In a modification (not shown) of the valve 100, the torsion spring 143, 243 directly acts on the motor shaft 135 or on any of the gear wheels 137a, 137b, 137c. It is also possible that the gear box 136 comprises an additional gear wheel for coupling the torsion spring 143, 243 to the valve drive 130.

[0130] In the case of power-failure, the resilient retainer element 43, 143, 243 first displaces the drive element 50 distally with respect to the piston 60 until the equalization pilot valve 80 is closed. As the equalization pilot valve 80 is closed, the fluid bleed increases the balancing pressure. The increased balancing pressure helps to urge the piston 60 distally into its abutment position. Further distal movement of the drive element 50 caused by the retainer element 50 ensures that equalization pilot valve 80 remains closed and entrains the piston 60. However, the primary driving force for closing the valve is the resilient force of the retainer element 43, 143, 243. The valves 1 , 100 will also be able to close without a pressure difference.

[0131] With regard to both valves 1 and 100, the threaded engagement between the spindle 40 and the drive member 50, 150 may be non-self-locking. Especially, a pitch of the threaded engagement between the spindle 40 and the drive member 50, 150 may be at least 3 mm per revolution, e.g. in the range from 3,5 mm to 6 mm per revolution. This ensures low resistance of the valve drive 30 against the resilient force of the returner element 43, 143, 243 in the case of power-failure. The returner element 43, 143, 143 can be less strong. Accordingly - as the motor 31 , 131 has to overcome less resilient force of the returner element 43, 143 for opening the valve 1 , 100 - the motor 31 , 131 can be less powerful and hence smaller, lighter, cheaper, and more efficient. Apart from that, the large pitch allows faster transition between the closed state and the fully open state with the same rotational speed of the motor 31 , 131.

[0132] The anti-rotation mechanisms 49 may comprises at least one spline 49a (e.g. antirotation wing) at one of the drive member 50, 150 and the valve body 10 and, at the other one of the drive member 50, 150 and the valve body 10, a corresponding slot 49b (or groove) for guiding the at least one spline 49a along the axial direction L. In the embodiments shown in the figures, the drive member 50, 150 includes two splines 49a engaging corresponding axial extending slots 49b formed in the valve body 49 (compare with Figs. 5, 11 , 14, and 15). In the valve 1 according to the first embodiment, the splines 49a are arranged at an outer circumference of the flange section 52.

[0133] In the valves 1 and 100 according to the exemplary embodiments, the axial extending slots 49b are formed on a side wall of the balancing chamber 20. The side wall of the balancing chamber 20 corresponds to an inner circumferential wall portion of the guiding insert 4, 104 circumventing the balancing chamber 20.

[0134] Guiding pins 68 may be formed at a distal end of the protruding portion 64 (see Fig. 13). The guiding pins 68 help to avoid lateral vibrations of the protruding portion 64. The valves 1 and 100 may be configured such that the total force applied onto the piston 60 by the fluid is always directed distally (i.e. towards abutment with the valve seat 13), in any opening degree of the valve 1 , 100.

[0135] Fig. 19 shows a flow control valve 300 of a third embodiment according to the present invention. The valve 300 has basically the same structure and functionalities as the valves 1 and 100. Identical reference signs are used for the same elements. In general, the explanations given with regard to the valves 1 and 100 and their components apply correspondingly to the valve 300. Only the differences are described in the following.

[0136] The valve 300 comprises a returner mechanism with two resilient returner elements 343a and 343b for automatically bringing the piston 60 to a predetermined state when the motor 31 is not powered. In this embodiment, the predetermined state is neither the closed state nor the fully open state but a partly open stated of the valve 300. In other words, in the predetermined state, the valve 300 has a predetermined opening degree which is less than a maximum opening degree. Fig. 19 shows the valve 300 in the predetermined state, in which the piston 60 is in a predetermined position, displaced away from abutment on the valve seat 13 (i.e. from its abutment position) by a predetermined distance PD. The predetermined distance is less than the maximum stroke MS between the abutment position of the piston rod 60 and its fully retracted position (not shown in Fig. 19 but in Fig. 5 relating to valve 1 ).

[0137] In this embodiment, the drive member 350 additionally includes a washer flange 346 at its outer circumference. Apart from that, the drive member 350 corresponds to the drive member 50 in Fig. 1 and has the same functionalities.

[0138] The returner mechanism includes the washer flange 346, a first resilient returner element 343a, a first washer 344a, a second resilient returner element 343b, a second washer 344b, and a stopper 307. Both resilient returner elements 343a and 343b are axial springs, in more detail cylindrical coil-type springs.

[0139] The first resilient returner element 343a is arranged between first washer 344a and the bearing plate 6a. The second resilient returner element 343b is arranged between the second washer 344b and a spring cup 308. The spring cup 308 is (at least axially) fixed with respect to the valve body 10, for example to the middle housing section 5. Further, the stopper 307 is (at least axially) fixed with respect to the valve body 10, for example to the middle housing section 5 as well.

[0140] The first washer 344a and the second washer 344b are axially movable with respect to the valve body 10. The stopper 307 limits the axial movements of the first washer 344a and the second washer 344b. In particular, it limits a distal axial movement of the first washer 344a and a proximal axial movement of the second washer 344b with respect to the valve body 10.

[0141] When the valve 300 is in the predetermined state as in Fig. 19, the first spring 343a urges the first washer 344a into abutment with (a motor-side) of the washer flange 346 and with stopper 307. At the same time, the second spring 343b urges the second washer 344 into abutment with (a piston-side) of the washer flange 346 and with the stopper 307. The stopper 307 can be an inward flange or projection, for example. Correspondingly, the piston 60 is held in its predetermined position with the predetermined distal PD from abutment onto the valve seat 13. The groove 75 opens partially into the inlet pressure chamber 12.

[0142] When the valve drive 30 (with the motor 31 ) moves the drive member 350 proximally with respect to the predetermined state (i.e. upwards in Fig. 19 as shown in Fig. 20), the washer flange 346 displaces the first washer 344a out of abutment with and proximally away from the stopper 307. The first resilient returner element 343a is (further) compressed. As soon as the motor 31 is not powered any longer, a resilient force of the first resilient returner element 343a pushes the first washer 344a distally back into abutment with the stopper 307. It hence urges the valve 300 back to its predetermined state. There is no influence of the second resilient member 343b on the driver member 350 as long as the washer flange 346 is separated from the second washer 344b.

[0143] When the valve drive 30 (with the motor 31 ) moves the drive member 350 distally with respect to the predetermined state (i.e. downwards in Fig. 19 as shown in Fig. 21 ), the washer flange 346 displaces the second washer 344b out of abutment with and distally away from the stopper 307. The second resilient returner element 343b is (further) compressed. When the motor 31 is not powered any longer, a resilient force of the second resilient returner element 343b pushes the second washer 344b back proximally into abutment with the stopper 307. It hence urges the valve 300 back to its predetermined state then. There is no influence of the first resilient member 343a on the driver member 350 as long as the washer flange 346 is separated from the first washer 344a.

[0144] List of reference signs:

[0145] 1 ; 100 valve

[0146] 2 lower housing section

[0147] 3 seat insert

[0148] 3a downstream-side wall

[0149] 3b rod guide channel

[0150] 4; 104 guiding insert

[0151] 5; 105 middle housing section

[0152] 6; 106 motor housing section

[0153] 6a bearing plate

[0154] 10 valve body

[0155] 11 (fluid) inlet

[0156] 11 a inlet port

[0157] 12 inlet pressure chamber

[0158] 13 valve seat

[0159] 13a fluid passage

[0160] 14 outlet pressure chamber

[0161] 15 (fluid) outlet

[0162] 15a outlet port

[0163] 20 balancing chamber

[0164] 25 fluid bleed

[0165] 26 labyrinth seal

[0166] 27 outer thread

[0167] 30; 130 valve drive

[0168] 31 ; 131 motor

[0169] 32; 132 (motor) chamber

[0170] 33; 133 rotor

[0171] 34; 134 stator

[0172] 35, 135 motor shaft 40 spindle

[0173] 41 outer thread

[0174] 43; 143; 243 returner element

[0175] 45 conversion mechanism

[0176] 49 anti-rotation mechanism

[0177] 49a spline

[0178] 49b (axial) slot

[0179] 50; 150; 350 drive member

[0180] 51 inner thread

[0181] 52 flange section

[0182] 53 seal member

[0183] 53a seal mount

[0184] 53b annular groove

[0185] 53c retainer ring

[0186] 54 hook structure

[0187] 54a receiving recess

[0188] 54b shoulder

[0189] 55 mechanical coupling

[0190] 57 first flange

[0191] 58 groove

[0192] 59 second flange

[0193] 60 piston

[0194] 60a main rod (of the piston)

[0195] 60b lower part (of the piston)

[0196] 60c threaded engagement

[0197] 61 drive-side end portion

[0198] 61 a tip

[0199] 62 middle portion

[0200] 64 protruding portion

[0201] 65 (outer) circumference 66 fluted part

[0202] 67 flow passage

[0203] 68 guiding pin

[0204] 70 equalization passage 71 balance chamber opening

[0205] 72 equalization opening

[0206] 73 supplementary equalization passage

[0207] 74 channel opening

[0208] 75 groove 80 equalization pilot valve

[0209] 90 flange section

[0210] 91 inward flange

[0211] 92 seal mount

[0212] 93 fluid passage 94 seal member

[0213] 95 retainer ring

[0214] 136 gearbox

[0215] 137a (first) gear wheel

[0216] 137b gear wheel 137c (last) gear wheel

[0217] 138 ball bearing

[0218] 143a; 243a first end (inner end)

[0219] 243b; 243b second end (outer end)

[0220] 307 stopper 308 spring cup

[0221] 343a first resilient returner element

[0222] 343b second resilient returner element

[0223] 344a first washer

[0224] 344b second washer 346 washer flange AX abscissa (axial displacement)

[0225] C central axis

[0226] EFS ordinate (effective flow cross section)

[0227] DP piston diameter DS nozzle sealing diameter

[0228] MR movement range

[0229] MS maximum stroke

[0230] PD predetermined displacement

[0231] L axial direction

Claims

Claims:1 . A flow control valve (1 ; 100), for example an expansion valve for a refrigeration system, of pressure-balanced piston type and with a mechanical fail-safe functionality, the valve (1 ; 100) comprising a valve body (10) with a fluid inlet (11 ), an inlet pressure chamber (12) which is fluidly connected with the fluid inlet (11 ), a fluid outlet (15), a valve seat (13) arranged between the inlet pressure chamber (12) and the fluid outlet (15), and a balancing chamber (20), a piston (60), and a valve drive (30) for controlling fluid flow from the fluid inlet (11 ) to the fluid outlet (15) through the valve seat (13) by displacing the piston (60) with regard to the valve seat (13) along an axial direction (L), wherein the valve drive (30) comprises a motor (31 ; 131 ) and a drive member (50; 150; 350), which is drivable by the motor (31 ; 131 ), for axially entraining the piston (60), wherein the piston (60) protrudes with a drive-side end portion (61 ) into the balancing chamber (20) and includes an equalization passage (70) with a first flow resistance from the drive-side end portion (61 ) to an equalization opening (72) that is in fluid connection with the fluid outlet (15), wherein the valve (1 ; 100) comprises a fluid bleed (25) from the inlet pressure chamber (12) and / or the fluid inlet (11 ) to the balancing chamber (20), wherein the fluid bleed (25) is separate from the equalization passage (70) and has a second flow resistance that is larger than the first flow resistance, andwherein the valve (1 ; 100) comprises an equalization pilot valve (80) for opening and closing the equalization passage (70).

2. The valve (1 ; 100) according to claim 1 , wherein the motor (31 ; 131 ) is a stepper motor and wherein the valve drive (30) includes a conversion mechanism (45) for converting rotational movements provided by the stepper motor (31 ; 131 ) into axial movements of the piston (60).

3. The valve (1 ; 100) according to claim 2, wherein the motor (31 ; 131 ) is a variable reluctance stepper motor.

4. The valve (1 ; 100) according to any one of the preceding claims, wherein at least a rotor (33; 133) of the motor (31 ; 131 ) is housed in a motor chamber (32; 132) that is in fluid connection with the balancing chamber (20).

5. The valve (1 ; 100) according to any one of the preceding claims, wherein the drive member (50; 150; 350) and the piston (60) form the equalization pilot valve (80), and wherein a mechanical coupling (55) between the drive member (50; 150; 350) and the piston (60) allows limited relative axial displacement of the drive member (50; 150; 350) relative to the piston (60) for opening and closing the equalization pilot valve (80).

6. The valve (1 ; 100) according to any one of the preceding claims, wherein the valve (1 ; 100) comprises, at a middle portion (62) of the piston (60) between the inlet pressure chamber (12) and the balancing chamber (20), a labyrinth seal (26) between the piston (60) and the valve body (10), wherein the labyrinth seal (26) forms part of the fluid bleed (25).

7. The valve (1 ; 100) according to any one of the preceding claims, wherein the valve (1 ; 100) comprises a resilient returner element (43; 143; 343a, 343b)for automatically bringing the piston (60) to a predetermined position when the motor (31 ) is not powered.

8. The valve (1 ; 100) according to any one of the preceding claims, wherein the drive member (50; 150; 350) is threadedly engaged with and drivable by a spindle (40), which is rotatable by the motor (31 ; 131 ), wherein a pitch (42) of the threaded engagement between the drive member (50; 150; 350) and the spindle (40) is 3 mm per revolution at the minimum.

9. The valve (100) according to claim claims 7 and 8, wherein the resilient returner element (143) is a torsion spring and acts directly on the spindle (40).

10. The valve (1 ; 100) according to any one of the preceding claims, wherein the equalization pilot valve (80) opens before the piston (60) lifts off from the valve seat (13) for opening the valve (1 ; 100).11 . The valve (1 ; 100) according to any one of the preceding claims, wherein the piston (60) comprises, at an outlet-side end in the axial direction (L) opposite to the drive-side end portion (61 ), a protruding portion (64) having an outer circumference (65) corresponding to an inner circumference of the valve seat (13), wherein said protruding portion (64) has at least one fluted part (66), wherein a flow passage (67) from the inlet pressure chamber (12) to the fluid outlet (15) through the valve seat (13) is defined between the at least one fluted part (66) and the valve seat (13) when the piston (60) is lifted off from the valve seat (13).

12. The valve (1 ; 100) according to claim 11 , wherein the piston (60) includes a supplementary equalization passage (73) for establishing a fluid connection between the inlet pressure chamber (12) and the equalization passage (70) when the piston (60) is lifted off from the valve seat (13), wherein the supplementary equalization passage (73) includes a channel opening (74) arranged inthe protruding portion (64) of the piston (60) outside from any one of the fluted parts (66).

13. The valve (1 ; 100) according to claim 12, wherein an effective flow cross- section (76) of the supplementary equalization passage (73) gradually increases with increasing axial displacement of the piston (60) towards the drive-end side over a predetermined movement range (MR) of the piston (60) along the axial direction (L).

14. The valve (1 ; 100) according to claim 12 or 13, wherein the supplementary equalization passage (73) has a groove (75) formed in a region of the outer circumference (65) of the protruding portion (64) comprising the channel opening (74), wherein the groove (75) extends along the axial direction (L) and is tapered with increasing cross-sectional area towards the outlet-side.

15. The valve (1 ; 100) according to any one of the preceding claims, wherein the valve drive (30) includes a gear box (136) between the motor (131 ) and the drive member (150).

Images