Patent Description:
Hydraulic snubbers, also referred to as pressure snubbers, are devices which are used to attenuate sharp pressure transients in liquids upstream of sensitive equipment. Many potential sources of sharp pressure transients exist, the most common ones perhaps being the shutting and opening of valves and pressure ripples from pumps. Similarly, various types of equipment sensitive to pressure transients exist, the most common in gas turbine engine applications likely being pressure sensors. For example, a pressure sensor construction can include a load cell applied against a diaphragm which is configured to elastically deform within a given pressure range, and the diaphragm is typically designed in a manner to reach a suitable trade-off between sensitivity and the extent of the pressure range. If the pressure range is exceeded, the diaphragm can plastically deform, which destroys the sensor. Hydraulic snubbers in the form of accessory fittings can be positioned in the liquid solid line, between the potential pressure transient source and the sensitive equipment. They can be used to avoid the loss of function of the sensitive equipment or to provide accurate readings (such as in the case of Bourdon tube pressure gauges). Pressure snubbers are typically configured to attenuate sharp pressure fluctuations (transients), such as may occur over a relatively small duration and/or with high frequency (such as less than one second). Indeed, the pressure fluctuations which pressure sensors are designed to monitor in liquid carrying lines of gas turbine engines can be of significantly longer duration, such as more than one second, for instance.

While existing pressure snubbers were satisfactory to a certain degree, there remained room for improvement. For example, in the case of oil lines in gas turbine engines, the oil temperature can vary significantly depending on the engine's operating conditions throughout the operating envelope, and the oil viscosity varies significantly with temperature. This particular kind of scenario can make it difficult to achieve required sharp pressure transients attenuation while maintaining sufficient sensor response. Moreover, cost, durability, maintenance load and weight are other example factors which can be relevant in providing a pressure snubber suitable for a given application.

<CIT> discloses a device for damping the oscillation of a pulsating liquid stream.

<CIT> discloses an inline fluid damper device.

<CIT> discloses means for limiting a temperature rise due to an abrupt alteration of the flow rate of gas under high pressure through a conduit.

The invention is an assembly in accordance with the technical features of claim <NUM>, a gas turbine engine in accordance with claim <NUM> and a method of installing a hydraulic snubber insert into a liquid line of a gas turbine engine in accordance with claim <NUM>.

<FIG> illustrates a gas turbine engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases.

The compressor <NUM>, fan <NUM> and turbine <NUM> have rotating components which can be mounted on one or more shafts. Bearings <NUM> are used to provide smooth relative rotation between a shaft and casing (non-rotating component), and/or between two shafts which rotate at different speeds. An oil lubrication system <NUM> including an oil pump <NUM>, sometimes referred to as a main pump, and a network of conduits and nozzles <NUM>, is provided to feed the bearings <NUM> with oil. Seals <NUM> are used to contain the oil. A scavenge system <NUM> having cavities <NUM>, conduits <NUM>, and one or more scavenge pumps <NUM>, is used to recover the oil, which can be in the form of an oil foam at that stage, from the bearings <NUM>. The oil pump <NUM> typically draws the oil from an oil reservoir <NUM>, and it is relatively common to use some form of air/oil separating device in the return line. A pressure sensor <NUM> can be used to monitor the oil supply operation, and can have a diaphragm exposed to the oil pressure in the oil supply line, for instance.

In one example, the pressure sensor <NUM> can form part of a low oil pressure (LOP) switch which, for instance, can be configured to shut down an auto-pilot system (APS) in the event where the pressure falls below a predetermined threshold. While during typical operation of the gas turbine engine, the average pressure in the oil line can vary slowly, typically not changing significantly within duration windows of more than one second, the instantaneous oil pressure can vary sharply due to the operation of the main pump. Indeed, in the case of a gear pump, for instance, the flowrate generated by the pump will not be constant, but rather minutely influenced due to the effect of individual ones of the gear teeth on the flow, producing relatively sharp, repetitive variations in pressure in duration windows of less than one second, and even in the <NUM>th of a second range. Depending on the operating conditions, such regular, sharp, decreases in pressure may be sufficient to toggle the low pressure switch, even though such high frequency pressure transients are not what the low pressure switch is configured to be responsive to.

One potential solution to this problem is to introduce a pressure snubber between the LOP switch and the pump <NUM>. However, looking into this more closely, there may be several design requirements for such a solution to be viable, such as : a) achieving sufficiently high attenuation rate for the pressure transient; b) achieving sufficiently low fill-up time (e.g. a minimum pressure signal threshold build up below <NUM> seconds, preferably in the order of <NUM> second or even less); and c) providing a solution versatile enough to address a range of oil temperatures (e.g. from -40F to 270F (-40C to 132C)), and the associated range of oil viscosity. There may also be a challenge in obtaining accurate pressure readings due to slowly released high pressure in a transducer cavity or in a restrictor.

Accordingly, one may consider using a pressure snubber coupling having a single orifice, but realize that if such a device was adjusted to provide sufficient attenuation for the application, it would then only be suitable for a range of oil temperatures smaller than the actual range of oil temperatures in the application. Alternately, if adjusting the orifice size for the achieving suitable fill-up time over the entire oil temperature range, one may not be able to achieve sufficient attenuation rate.

As will be explained below in further detail, it was found that such limitations could be addressed by using a composite pressure snubber formed of a plurality of orifices, such as, for instance, a sequence of segments each having one or more orifice. However, this leaves the issues of achieving satisfactory costs, convenience, and weight.

It was found that such latter considerations could satisfactorily be addressed, at least in some embodiments, by providing the pressure snubber in the form of an insert designed to be introduced within an existing liquid carrying line, as opposed to, say, a coupling configured to be assembled in line between the sensor outlet of the line and the sensor. The insert can have a plurality of segments mounted to a stem via which the segments can be pushed into or pulled out from the liquid carrying line, for instance, and even held longitudinally in place during operation such as by way of one form or another of a retainer which can be provided at a proximal end of the stem and secured into place during operation for instance. The stem is flexible to make the hydraulic snubber insert adaptable to curvilinear liquid lines. The stem can be made of a metal wire, and the segments can be secured to the stem, such as by being made of a polymer or other metal overmoulded onto the stem, for instance. Alternatively, the insert can be designed in a manner to be a single moulded component, for instance. Using a stem which is flexible while having a certain amount of compressive strength, can allow to provide for the possibility of introducing the insert into a curvilinear conduit, for instance, allowing the insert to be usable in a manner somewhat akin to how a drain snake is used in unclogging curved drain pipes. Examples are presented below in association with a gas turbine engine context, but it will be understood that the proposed solution appears significantly original, and may benefit from use in contexts other than gas turbine engine contexts.

<FIG> shows an example embodiment of a pressure snubber <NUM> formed by a hydraulic snubber insert <NUM> introduced into an existing liquid carrying line <NUM>, upstream of a sensitive equipment such as a pressure sensor <NUM>. In this embodiment, the snubber insert <NUM> has an elongated stem <NUM> which is made of a sturdy, yet flexible material. The amount of required flexibility can depend on the minimum bend radius in the liquid carrying line <NUM>, for instance, and for straight lines, one may prefer using a rigid material metal wire or braided line for the stem <NUM>. The snubber insert <NUM> further has at least one segment <NUM>, typically a plurality, which extend transversally from the stem <NUM>. "Transversally", here, is used relative to refer to an orientation generally normal to the length of the stem <NUM>. The segments <NUM> are interspaced from one another along the length of the stem <NUM> and have a cross-sectional size and shape generally mating the cross-sectional size and shape of the liquid carrying line they are intended to fit.

Each one of the segments <NUM> has at least one aperture <NUM>, preferably more than one aperture <NUM>, such as perhaps best seen in <FIG>. The apertures <NUM> can be provided in the form of open shapes such as "dents" formed along the periphery of the corresponding segment's outer edge, such as shown in <FIG>, and form a portion of the outer edge, but can alternately be closed shapes radially recessed from the outer edge. In this embodiment, each segment <NUM> has three equidistant semi-circular orifices along its outer edge such as shown in <FIG>. The insert <NUM> can be handled via the stem <NUM>, and therefore, by pushing the stem <NUM>, the segments which can snugly fit the liquid carrying conduit can be pushed while being frictionally engaged with the inner surface (wall) of the liquid carrying conduit <NUM>. The segments <NUM> can also be pulled out from the conduit by pulling the stem <NUM>, which can remain externally accessible even when the insert <NUM> has been pushed into the position of use, which can be referred to as the snubbing position. The amplitude of the pressure transient can drop by a given step across each segment, due to the decrease in cross-sectional area through the segment (or otherwise said, through the at least one aperture per segment). In an alternate embodiment, the insert can include a single segment instead of a plurality of segments, for instance.

The insert can also have a retainer <NUM>, which would typically be positioned at an end <NUM> of the insert opposite the end <NUM> which is first introduced into the liquid carrying line through the sensor aperture. The retainer <NUM> can be configured to abut against a corresponding end of the liquid carrying line <NUM>, and therefore prevent the insert from being pulled deeper into the liquid carrying line <NUM> during operation. The retainer <NUM> can be configured to become trapped into place when the sensor <NUM> or other sensitive equipment is secured at the end of the liquid carrying line <NUM>. In this embodiment, the insert has two retainers <NUM>, one at each end <NUM>, <NUM>, and the insert is symmetrical and can alternately be engaged into the conduit via either end <NUM>, <NUM>. In alternate embodiments, the insert <NUM> may have a single retainer, or be provided without a retainer. In this embodiment, the retainer <NUM> also extends transversally, is cruciform, having four arms, and the tips of the arms can engage an flat annular edge surrounding the conduit's bore, thereby preventing the insert from being pulled further into the conduit due to vibrations or the like, for instance. Another component, such as a pressure sensor, can be secured to the end of the conduit and trap the retainer between the component and the annular edge, for instance, also preventing the insert from exiting the conduit unless the component is removed.

The exact configuration of the snubber insert <NUM> can vary depending on the embodiment. Indeed, many variables can be controlled in a manner to arrive to a suitable solution for the specific embodiment, such as the geometry of the apertures, the size of the apertures, the number of orifices per segment, the number of segments, the downstream volume (between the last segment and the sensitive equipment - it will be noted that to a certain extent, this volume can be controlled by the free length of stem extending between the end <NUM> of the insert <NUM> and the closest segment), and even the configuration of the apertures relative to one another, e.g. whether successive apertures are aligned with one another or clocked/rotated relative to one another - such as shown in <FIG> (alternatively, the clocking can be by <NUM> degrees to produce a zig-zag pressure pattern), or whether the geometry is otherwise varied from one segment to another (e.g. progressively increasing or reducing the open surface area from one segment to another).

We will now illustrate one possible example of how a snubber insert <NUM> can be specifically adapted to a specific embodiment by variations in some of the aforementioned variables.

Indeed, as explained in the "<NPL>, the concept of Lohm rate can be used to select an appropriate attenuation rate for a given frequency of pressure ripple in pump applications.

One can reduce the Lohm rate (L) by increasing hole diameter (d) in accordance with the formula : <MAT> with the diameter expressed in inches. In the case of parallel flows (i.e. multiple apertures per segment), the total Lohm rate LT for one segment can be expressed as <MAT> where L<NUM>, L<NUM>, LN are the respective Lohm rates of apertures <NUM>, <NUM>. In the case of series flow, the total Lohm rate is <MAT>.

Lohm rate can also change as a function of geometry. For instance, comparing triangular (<NUM>°) cuts such as shown in <FIG> and semi-circular cuts such as shown in <FIG>, for different cut depths, one can produce the graph presented in <FIG> showing the resulting cross-sectional area of the aperture. Plotting for different cut depths and different orifice geometries leads to the resulting Lohm rates plotted in <FIG>. Similarly, the graph of <FIG> presents Lohm rate for varying numbers of segments, comparing cases of one aperture per segment (top) progressively to <NUM> orifices per segment (bottom).

Accordingly, one can achieve a desired Lohm rate in various ways, by tuning different variables, which can produce different effects on response time, allowing for versatility. Indeed, it has been observed that orifice geometry, for instance, can define cross-section area which directly translates to attenuation rate which single orifice can provide (Lohm rate). The geometry can have a significant impact on tolerance definition and overall feasibility of the solution. For instance, in the case of a semi-circular cut orifice with a radius of <NUM> inches and a tolerance of ± <NUM>, the Lohm rate can change by roughly ± <NUM>% in the case of a single orifice. The orifice size can have a significant impact on cross-section area which can directly translate to attenuation rate which a single orifice can provide (Lohm rate). The number of orifices both in a segment and in a row change the overall attenuation rate. In a single segment, more orifices in a segment decreases attenuation rate for a segment, whereas in a row, more orifices in a row increases the attenuation rate for the entire wire. Increasing downstream volume can also decrease required attenuation rate. In the case of segments having open-shaped apertures formed in the outer edge, the unapertured portions of the segments can seal the flow by applying pressure on the inner surface of the conduit.

Indeed, <FIG> shows one such alternate embodiment of a pressure snubber <NUM> formed by a hydraulic snubber insert <NUM> introduced into an existing liquid carrying line <NUM>. In this embodiment, the snubber insert <NUM> has an elongated stem <NUM> which is made of a sturdy, yet flexible material. The snubber insert <NUM> further has a plurality of segments which extend transversally from the stem <NUM>. "Transversally", here, is used relative to refer to an orientation generally normal to the length of the stem <NUM>. The segments <NUM> are interspaced from one another along the length of the stem <NUM> and have a cross-sectional size and shape generally mating the cross-sectional size and shape of the liquid carrying line they are intended to fit.

Each one of the segments <NUM> has a single aperture <NUM> such as seen in <FIG>. The apertures <NUM> can be provided in the form of open shapes such as "dents" formed along the periphery of the corresponding segment's outer edge, such as shown in <FIG>, and form a portion of the outer edge. The insert <NUM> can be handled via the stem <NUM>, and therefore, by pushing the stem <NUM> (which can be handled directly or via other segments or a retainer), the segments <NUM> which snugly fit the liquid carrying conduit can be pushed while being frictionally engaged with the inner surface (wall) of the liquid carrying conduit <NUM>. The segments <NUM> can also be pulled out from the conduit by pulling the stem <NUM>, which can remain externally accessible even when the insert <NUM> has been pushed into the snubbing position. The amplitude of the pressure transient can drop by a given step across each segment <NUM>, due to the decrease in cross-sectional area through the segment <NUM> (or otherwise said, through the at least one aperture <NUM> per segment <NUM>).

The insert <NUM> can also have a retainer <NUM> positioned at an end <NUM> of the insert. The retainer <NUM> can be configured to abut against a corresponding end of the liquid carrying line <NUM>, and therefore prevent the insert from being pulled deeper into the liquid carrying line <NUM> during operation. The retainer <NUM> can be configured to become trapped into place when the sensor <NUM> or other sensitive equipment is secured at the end of the liquid carrying line <NUM>. Another component, such as a pressure sensor <NUM>, can be secured to the end of the conduit and trap the retainer <NUM> between the component and the annular edge, for instance, also preventing the insert <NUM> from exiting the conduit unless the component is removed.

Depending on the embodiment, the insert can have a phase offsetting effect in addition to an attenuation effect. This is illustrated in <FIG> which shows two superposed pressure graphs, one at the outlet of a pump exhibiting significant pump ripple (upstream of the insert), and the second one immediately upstream of the sensor. As seen, the insert, in this embodiment, has the effect of significantly attenuating the pressure ripple from the pump, and also slightly offsets the phase of the pressure ripple.

The insert <NUM>, <NUM> can be inserted directly into the liquid carrying line at the time of manufacturing the gas turbine engine. Alternately, the insert <NUM>, <NUM> can be retrofitted to an existing gas turbine engine, several months or years after manufacturing the gas turbine engine.

For instance, <FIG> shows an example of a solid tube or flexible sensing line referred to herein as a liquid carrying line <NUM> used between a gearbox <NUM> and a low oil pressure sensor <NUM> in a gas turbine engine. The liquid carrying line <NUM> can be a liquid carrying line <NUM> about to be installed in a new gas turbine engine, in which case the insert can be introduced <NUM> into the liquid line by pushing it along an inner wall of the line via the stem. Its end can be initially introduced via either end of the liquid line. As shown in <FIG>, the liquid line can then be installed <NUM> by connecting it to the engine at one end, and to the sensor at the other end. Alternately, the liquid carrying line <NUM> can be an existing liquid carrying line <NUM> of a gas turbine engine having several years of service for instance, in which case the liquid carrying line <NUM> will first be disassembled <NUM>, <NUM>, from either the engine side, the sensor side, or both the engine side and the sensor side. If disassembled from the engine side, the liquid carrying line <NUM> can be disassembled from the gearbox <NUM> for instance. If disassembled from the sensor side, the liquid carrying line <NUM> can be disassembled from the low oil pressure sensor, for instance. Accordingly, the aperture of the liquid carrying line through which the insert is introduced can be a few parts of a sensing apparatus, such as fluid carrying line, ferrule, fitting, sensor passage leading to pressure chamber with diaphragm, to name a few examples.

<FIG> shows another example method of installing the insert <NUM>, which includes introducing <NUM> a first end of the insert into the liquid line via the sensor end, and therefore through the aperture onto which the sensor is installed (referred to as the sensor aperture hereinafter), and pushing the insert into the liquid line. This can include pushing at least one segment in friction sliding engagement along an inner wall of the liquid line via a stem (directly or indirectly), the segment protruding transversally from the stem. In the case of a retrofit application, reaching this step <NUM> can require removing a sensor <NUM> (either in good condition or damaged) from the sensor aperture, and the step <NUM> will likely be followed by replacing <NUM> a sensor (the same one or a new one in the case of a damaged sensor). If the insert has a retainer, the sensor can trap the retainer into place, preventing the snubber insert from moving thereafter via the stem. A retrofit application can also involve an optional step of removing <NUM> an existing hydraulic snubber device and replacing it with the hydraulic snubber insert. The existing hydraulic snubber device can be a pressure ripple snubber fitting secured between the sensor and the line, for instance.

The embodiments described in this document provide non-limiting examples of possible implementations of the present invention.

Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present invention as defined in the appended claims.

Claim 1:
An assembly comprising a liquid carrying line (<NUM>; <NUM>; <NUM>) of a gas turbine engine (<NUM>) and a hydraulic snubber insert (<NUM>; <NUM>) for the liquid carrying line (<NUM>; <NUM>; <NUM>), the insert (<NUM>; <NUM>) comprising an elongated stem (<NUM>; <NUM>) and at least one segment (<NUM>; <NUM>) extending transversally from the stem (<NUM>; <NUM>), each segment (<NUM>; <NUM>) having a size and shape mating a cross-sectional size and shape of the liquid carrying line (<NUM>; <NUM>; <NUM>), and having at least one aperture (<NUM>; <NUM>), the insert (<NUM>; <NUM>) being configured for the at least one segment (<NUM>; <NUM>) to be pushable snugly inside and along the liquid carrying line (<NUM>; <NUM>; <NUM>) and pullable out from the liquid carrying line (<NUM>; <NUM>; <NUM>) via the stem (<NUM>; <NUM>), wherein the stem (<NUM>; <NUM>) is flexible, characterised in that:
the liquid carrying line (<NUM>; <NUM>; <NUM>) is curvilinear; and in that
the at least one segment (<NUM>; <NUM>) includes a plurality of segments (<NUM>; <NUM>) interspaced from one another along a length of the stem (<NUM>; <NUM>), and at least one of :
a number of the plurality of segments (<NUM>; <NUM>);
a number of said at least one aperture (<NUM>; <NUM>) per segment (<NUM>; <NUM>)
a configuration of said at least one aperture (<NUM>; <NUM>) per segment (<NUM>; <NUM>);
a shape of the apertures (<NUM>; <NUM>); and
a configuration of the at least one aperture (<NUM>; <NUM>) in each segment (<NUM>; <NUM>) relative to the at least one aperture (<NUM>; <NUM>) of the other segments (<NUM>; <NUM>),
are configured to provide a substantial attenuation of repetitive pressure transients of a pump in liquids in the form of pressure ripples during operation of the gas turbine engine (<NUM>) while preserving response time of slower pressure variations across the hydraulic snubber insert (<NUM>; <NUM>) via the apertures (<NUM>; <NUM>).