Patent Application
20190323526
This application claims priority to European Patent Application No. 18461550.8 filed Apr. 19, 2018, the entire contents of which is incorporated herein by reference.
This disclosure relates to a nozzle housing for a flapper servo valve. This disclosure also relates to a flapper servo valve and a method of positioning a nozzle in a flapper servo valve.
Flapper servo valves are well-known in the art and can be used to control the flow of hydraulic fluid to an actuator via a spool valve. Typically, a flapper is deflected by an armature connected to an electric motor away or towards nozzles, which control fluid flow to the spool valve. Deflection of the flapper can control the amount of fluid injected from the nozzles, and thus the amount of fluid communicated to the actuator via the spool valve. In this way, servo valves can allow precise control of actuator movement.
Flapper servo valves include a housing that houses the components in cavities therein. The nozzles are normally separately formed and then interference fitted into a nozzle cavity within the housing, and their position is carefully calibrated to ensure accurate operation of the servo valve. In order to calibrate the positioning of the nozzle, the nozzle is moved axially within the cavity, usually using a calibration tool. Due to the tight tolerance needed for the interference fit, the nozzle edges can sometimes interfere with the surface of the cavity during axial movement of the nozzle. This can cause scraping off of some material from the cavity surface or the nozzle, which can cause contamination in the servo valve that can get between the nozzles and the flapper and prevent accurate control of the servo valve, or cause a complete malfunction. If the nozzle material is harder than the surrounding housing material (or vice versa), this problem can be more acute, as the softer material may be scraped off more easily.
From one aspect, the present disclosure relates to a nozzle housing for a flapper servo valve. The nozzle housing comprises a nozzle cavity for housing a nozzle, and a flapper cavity for housing a flapper. The nozzle cavity comprises a first open end and an opposing, second open end, wherein the first open end opens to the exterior of the nozzle housing and the second open end opens into the flapper cavity. The nozzle cavity further comprises a first cylindrical portion for receiving a nozzle inserted into the nozzle cavity from the first open end, a second cylindrical portion configured to hold the nozzle in its operating position, and a third cylindrical portion positioned between the first and second cylindrical portions for centering the nozzle prior to positioning in the second cylindrical portion. The first, second and third cylindrical portions are coaxial, and the diameter of the third cylindrical portion is smaller than the diameter of the first cylindrical portion but larger than the diameter of the second cylindrical portion. The nozzle cavity further comprises a first transition portion connecting the first cylindrical portion to the third cylindrical portion, and a second transition portion connecting the third cylindrical portion to the second cylindrical portion.
In certain embodiments of the above nozzle housing, the first cylindrical portion is adjacent the first open end, and either extends directly therefrom or is connected thereto via another portion (e.g. such as a threaded portion, which may be used to receive a housing plug and/or calibration tool). In addition or alternatively, the second cylindrical portion is at or adjacent the second open end and may extend directly therefrom.
By “operating position” it is meant the final position in which a nozzle is fixed for operation when used in a flapper servo valve. As will be understood by the skilled person, a nozzle in its operating position will generally be fixed in position near or at the second open end, proximate the flapper cavity. Such positioning provides reliable metered communication of fluid to the flapper of the flapper servo valve.
By “configured to hold” it is meant that the relative dimensions of the nozzle and the second cylindrical portion are suitable to provide an interference fit therebetween. As will be understood by the skilled person, this may mean the diameters of the nozzle and second cylindrical portion are substantially similar, or that the nozzle has a slightly larger diameter than the second cylindrical portion, for example, 3-10 μm larger.
By “cylindrical portion” it is meant that the portions have a substantially fixed diameter along their axial length. By “substantially” it is meant that the diameter may vary along the axial length due to standard manufacturing tolerances. It is to be understood that within the scope of this disclosure the cylindrical portions may be interrupted by certain variations, such as apertures or ports opening into the portions, without depriving them of cylindrical character.
By “transition portion” it is meant that the portions provide a transition between the diameters of different cylindrical portions. In other words, the diameter of the nozzle cavity decreases across the axial length of the transition portion.
In further embodiments of any of the above nozzle housings, the first and second transition portions comprise a chamfer. In other words, the diameter of the nozzle cavity decreases linearly across the axial length of the transition portion. In other embodiments, the transition portions are a rounded surface or are a step transition. In such embodiments, the diameter of the nozzle cavity decreases non-linearly across the axial length of the transition portions.
In further embodiments of any of the above nozzle housings, the nozzle housing further comprises a fluid port that opens to the third cylindrical portion to allow communication of fluid to the nozzle cavity.
In further embodiments of any of the above nozzle housings, the axial length of the first cylindrical portion is between 50-75% of the axial length of the second cylindrical portion, and the third cylindrical portion is between 30-60% of the axial length of the second cylindrical portion. These axial lengths ensure a nozzle can be easily inserted into the nozzle cavity, without undue misalignment, and that the nozzle will be successfully aligned by the third cylindrical portion, without encroaching on the axial length of the second cylindrical portion.
In further embodiments of any of the above nozzle housings, at least a portion of the surface of the nozzle cavity is anodised for reducing friction between a nozzle and the nozzle cavity during insertion and positioning of the nozzle in the nozzle cavity.
In further embodiments of any of the above nozzle housings, the nozzle housing comprises aluminium.
From another aspect, the present disclosure relates to a flapper servo valve. The flapper servo valve comprises the nozzle housing of any of the above discussed embodiments and a nozzle disposed within the nozzle cavity.
In an embodiment of the above flapper servo valve, the nozzle comprises a harder material than the nozzle housing.
In a further embodiment of either of the above flapper servo valves, the nozzle comprises stainless steel, and in one specific example, comprises stainless steel 304.
In a further embodiment of any of the above flapper servo valves, at least a portion of the surface of the nozzle is anodised for reducing friction between the nozzle and the nozzle cavity during insertion and positioning of the nozzle in the nozzle cavity.
In a further embodiment of any of the above flapper servo valves, the flapper servo valve further comprises a flapper disposed in the flapper cavity. In additional embodiments, the flapper is operatively connected to an armature, which is configured to rotate and move the flapper in response to an input, such as known in the art.
In a further embodiment of any of the above flapper servo valves, the flapper servo valve further comprises a second nozzle cavity at an opposing side of the flapper cavity to the first nozzle cavity, and a second nozzle disposed in the second nozzle cavity.
From yet another aspect, the present disclosure relates to a method of positioning a nozzle in the flapper servo valve of any of the above embodiments. The method comprises inserting the nozzle into the nozzle cavity via the first open end, and moving the nozzle axially through the nozzle cavity from the first cylindrical portion to the second cylindrical portion via the third cylindrical portion, wherein the third cylindrical portion acts as a guide to axially align the nozzle with the second cylindrical portion during the moving.
In an embodiment of the above method, the method further comprises the step of interference fitting the nozzle in the second cylindrical portion to hold the nozzle in its operating position.
In a further embodiment of the above method, the step of interference fitting the nozzle in the second cylindrical portion comprises using a calibration tool. Such calibration tools are well-known to the skilled person and one such tool is known from EP 3,205,913.
Some exemplary embodiments of the present disclosure will now be described by way of example only, and with reference to the following drawings in which:
With reference to
Although a pair of nozzles 6 and nozzle cavities 10 are shown in
With reference to
The nozzle cavity comprises a first cylindrical portion 110 and a second cylindrical portion 120 connected by a transition portion 115. First and second cylindrical portions 110, 120 are coaxial and are centred along central nozzle cavity axis X. The first cylindrical portion 110 has a larger diameter than the second cylindrical portion 120 and the nozzle 6, for example, 10-15% larger and is designed to receive the nozzle 6 from the first open end 100a. The smaller diameter second cylindrical portion 120 is a similar diameter to that of the nozzle 6, and once the nozzle 6 has been moved in to the appropriate operating position therein, the second cylindrical portion 120 is used to provide an interference fit with the nozzle 6 to hold it in place during use. The change in diameter from the first and second cylindrical portions 110, 120 is quite abrupt, and if the nozzle 6 is inserted off-axis (i.e. not exactly parallel to the nozzle cavity axis X) the nozzle 6 can interfere with the nozzle cavity surface and can scrape off material from the nozzle housing 108, (or from the nozzle 6) which can then become trapped in the nozzle cavity 10. This can lead to contamination or malfunction of a flapper servo valve comprising the nozzle housing 108.
With reference to
The nozzle cavity 10 comprises a first cylindrical portion 12, a second cylindrical portion 16 and a third cylindrical portion 14 positioned therebetween. First, second and third cylindrical portions 12, 14, 16 are coaxial, and are centred along central nozzle cavity axis X. The first cylindrical portion 12 receives the nozzle 6 inserted into the nozzle cavity 10 from the first open end 10a, the second cylindrical portion 16 is configured to hold the nozzle in its operating position (such as described above in relation to
The diameter D3 of the third cylindrical portion 14 is smaller than the diameter D1 of the first cylindrical portion 12, for example, 3-7% smaller but larger than the diameter D2 of the second cylindrical portion 16 and the nozzle 6, for example, 3-7% larger. The third cylindrical portion 16 having an intermediate diameter between the first and second cylindrical portions 14, 16 provides a less abrupt transition between nozzle portions, which allows successful alignment of the nozzle 6 with the second cylindrical portion 16 during insertion.
The axial length of the first cylindrical portion 12 may be between 50-75% of the axial length of the second cylindrical portion 16, whilst the axial length of the third cylindrical portion 14 may be between 30-60% of the axial length of the second cylindrical portion 12. In relation to the nozzle 6, the axial length of the second cylindrical portion 16 may be 90-120% of the axial length of the nozzle 6, whilst the axial length of the first cylindrical portion 12 may be 50%-75% of the axial length of the nozzle 6 and the third cylindrical portion 14 may be 30-50% of the axial length of the nozzle 6. These relative dimensions ensure that the second cylindrical portion 16 has sufficient axial length to accommodate the majority or all of the axial extent of the nozzle 6, such that it doesn't adversely interfere with the fluid flow in the nozzle cavity 10 (e.g. in the depicted example, such that it doesn't block port 8a); the third cylindrical portion is of sufficient axial length to allow successful alignment of the nozzle 6 with the second cylindrical portion 16; and the first cylindrical portion 12 is of sufficient axial length to provide easy insertion of the nozzle 6 into the nozzle cavity 10 without incurring undue misalignment.
The third cylindrical portion 14 is connected to the first cylindrical portion 12 by a first transition portion 13, and the third cylindrical portion 14 is connected to the second cylindrical portion 14 by a second transition portion 15. The depicted transition portions 13, 15 comprise chamfers, which provide a constant decrease in diameter across their length, to provide a smoother transition between the cylindrical portions 12, 14, 16 that further reduces the risk of the nozzle 6 having damaging interference with the nozzle cavity surface during insertion and positioning. However, in other embodiments, the transition portions 13, 15 could alternatively comprise any other suitable shape, such as a rounded surface or a step transition between the cylindrical portions 12, 14, 16.
In the depicted embodiment, there is also a third transition portion 11 that connects the first cylindrical portion 12 to the exterior of the nozzle housing 8. The third transition portion 11 may share the above discussed shape characteristics relating to the first and second transition portions 13, 15, and may provide easier initial insertion of the nozzle 6 into the nozzle cavity 10.
The nozzle housing 8 can be manufactured from any suitable manufacturing technique, such as casting, subtractive or additive manufacturing as would be apparent to the skilled person in the art. One example manufacturing technique is to cast the housing and use iterative drilling operations to create co-axial cavities of increased diameters (e.g. D2 to D3 to D1) at shorter drilling depths (e.g. portion lengths) to provide the nozzle cavity 10 with the first, second and third cylindrical portions. Alternatively, the housing 8 may be cast using appropriate moulds and inserts or build up layer by layer using a 3D printing additive manufacturing technique.
The depicted nozzle housing 8 may be made out of aluminium, whilst the nozzle 6 (which is normally exposed to harsher operating conditions) may be made of stainless steel, for example, stainless steel 304. These materials allow a flapper servo valve that can withstand the operating conditions necessary, whilst being relatively lightweight. Nonetheless, this material choice means the nozzle material is harder than the housing material, which may exacerbate the material scraping effect that can occur during nozzle insertion and positioning.
In some embodiments, at least a portion of the surface of the nozzle cavity 10 and/or nozzle 6 is anodised in order to reduce the friction generated between the nozzle 6 and the nozzle cavity 10 during insertion and positioning of the nozzle 6.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18461550.8 | Apr 2018 | EP | regional |
