Abstract:
The subject matter of this specification can be embodied in, among other things, a method that includes providing a fluid at a fluid inlet fluidically connected to an input fluid path, providing a fluid outlet fluidically connected to an outlet fluid path, fluidically connecting the inlet fluid path to the outlet fluid path through a valve, fluidically connecting the inlet fluid and the outlet fluid through a bypass fluid path in parallel with the valve, flowing the fluid from the inlet fluid path to the outlet fluid path through the valve and the bypass fluid path at a regulated fluid flow rate, restricting fluid flow in the bypass fluid path with a first orifice, restricting fluid flow in one of the fluid inlet path or the fluid outlet path with a second orifice, and providing the fluid at the fluid outlet at an outlet fluid flow rate.

Description:
TECHNICAL FIELD 
     The concepts herein relate to fluid flow regulators and more particularly to fluid flow regulators with damped regulation responses. 
     BACKGROUND 
     Flow regulating valves are integral components to providing a constant flow rate of fluid as requested by an external command to a combustion chamber, regardless of the inlet flow at the flow regulating valve. Historically, flow regulating valves have been damped with either a laminar leak path or via orifices in non-flowing sense lines. 
     Laminar leak path damping can provide linear damping over the full range of valve velocities. However the damping is proportional to the kinematic viscosity of the fluid being regulated, therefore the damping is sensitive to temperature variations of the fluid media. 
     Non-flowing orifice damping exhibits less temperature sensitivity than valves using laminar leak path damping. However, non-flowing orifice damping is proportional to the square of valve velocity. As a result, the orifice provides no damping when the valve is stationary (e.g., valve velocity equal to zero), but can over-damp the valve during large disturbances. 
     SUMMARY 
     In general, this document describes fluid flow regulators. 
     In a first aspect, a fuel flow regulator system for regulating flow through a fuel delivery path includes a fuel flow regulator valve in the fuel delivery path operable to selectively provide a restriction in the fuel delivery path in response to a fuel fluid flow between a fluid inlet and a fluid outlet, a bypass fluid path fluidically connecting the fluid inlet and the fluid outlet in parallel with the regulator valve, a first orifice restricting the bypass fluid path, and a second orifice restricting one of the fluid inlet or the fluid outlet. 
     Various implementations can include some, all, or none of the following features. The second orifice can restrict the fluid outlet. The fluid flow regulator can include a third orifice restricting the fluid inlet. The first orifice can have a size selected based on a minimum fluid flow rate. The outlet fluid flow rate can be the sum of the minimum fluid flow rate and the regulated fluid flow rates. The second orifice can have a size selected based on a bypass path flow rate, and the outlet flow rate is the sum of the minimum fluid flow rate, the bypass path flow rate, and the regulated fluid flow rate. The bypass flow path can include a filter screen configured to resist the flow of ice or contaminant particle flow. The bypass flow path can include a heating element. 
     In a second aspect, a method of regulating fluid flow includes providing a fluid at a fluid inlet fluidically connected to an input fluid path, providing a fluid outlet fluidically connected to an outlet fluid path, fluidically connecting the inlet fluid path to the outlet fluid path through a valve, fluidically connecting the inlet fluid and the outlet fluid through a bypass fluid path in parallel with the valve, flowing the fluid from the inlet fluid path to the outlet fluid path through the valve and the bypass fluid path at a regulated fluid flow rate, restricting fluid flow in the bypass fluid path with a first orifice, restricting fluid flow in one of the fluid inlet path or the fluid outlet path with a second orifice, and providing the fluid at the fluid outlet at an outlet fluid flow rate. 
     Various implementations can include some, all, or none of the following features. The second orifice can restrict the fluid outlet. The fluid flow regulator can include a third orifice restricting the fluid inlet. The first orifice can have a size selected based on a minimum fluid flow rate. The outlet fluid flow rate can be the sum of the minimum fluid flow rate and the regulated fluid flow rates. The second orifice can have a size selected based on a bypass path flow rate, and the outlet flow rate is the sum of the minimum fluid flow rate, the bypass path flow rate, and the regulated fluid flow rate. The bypass flow path can include a filter screen configured to resist the flow of ice or contaminant particle flow. The bypass flow path can include a heating element. 
     The systems and techniques described here may provide one or more of the following advantages. First, a system can provide damping of the flow regulator that is independent of amplitude by using a flowing damping orifice damping arrangement. Second, the system can be arranged such that there are no additional pump draw requirements, thereby having no impact to pump sizing. Third, the system can implement larger diameter passages than other damping systems, thereby improving the resistance to contamination. Fourth, the system can have reduced leakage sensitivity. Fifth, the system can eliminate the need for one or two check valves that may be required when using prior damping arrangements. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1 and 2  are schematic diagrams of prior art fluid flow regulators. 
         FIG. 3  is a schematic diagram of an example fluid flow regulator. 
         FIG. 4  is a schematic diagram of an example fluid delivery system that includes an example fluid flow regulator with damping. 
         FIG. 5  is a schematic diagram of another example fluid delivery system that includes another example fluid flow regulator with damping. 
         FIG. 6  is a schematic diagram of another example fluid delivery system that includes another example fluid flow regulator with damping. 
         FIG. 7  is a schematic diagram of another example fluid delivery system that includes another example fluid flow regulator with damping. 
     
    
    
     DETAILED DESCRIPTION 
     This document describes systems and techniques for regulating fluid flow with a damped response. Flow regulating valves can maintain the flow of fluid provided at the inlet of the flow regulator. Two damping schemes used for flow regulator systems include the use of laminar leak path damping or orifices in non-flowing sense lines. 
       FIG. 1  is a schematic diagram of a prior art fluid flow regulator  100  that uses laminar leak path damping. The regulator  100  includes two distinct pressure signals at  102  and  104 . The fluid at  102  is fluidically connected to fluid path  106 , and the fluid at  104  is fluidically connected to fluid path  108 . 
     The fluid path  106  is fluidically connected to the outlet fluid path  108  through a bypass valve  110  and a laminar damping orifice  120 . The bypass valve  110  includes a number of ports (not shown) that fluidically connects the inlet fluid path  130  to the outlet fluid path  140 . The bypass valve  110  exhibits a regulator velocity, generally represented by the arrow  112 . The laminar damping orifice  120  restricts fluid flow from the fluid inlet  102  to the bypass valve  110 . The laminar damping orifice  120  includes a close clearance gap through which fluid can flow in a damped manner. 
     Laminar leak path damping can provide linear damping over a substantial range of valve velocities. However, the damping is proportional to the kinematic viscosity of the fluid being regulated, therefore the damping is sensitive to temperature variations of the fluid media. At low regulator velocities  112  of the bypass valve  110 , low flow is induced across the laminar damping orifice  120 . The flow across laminar damping orifice  120  results in a differential pressure drop that is proportional to flow (e.g., linear). In addition, laminar flow is inversely proportional to fluid kinematic viscosity. Therefore, damping varies with the temperature of the fluid being flowed. For example, typical aircraft fuels and operational temperature ranges can result in fuel viscosity variations from 20.6 centistokes (−65 F JetA) to 0.4 centistokes (300 F JetA), resulting in temperature-induced damping variations of approximately 50×. Such levels of damping variation can be difficult to design for over an entire operating envelope of an aircraft engine. As such, the laminar leak path damping architecture of the regulator  100  may be seldom implemented with modern aircraft engine embodiments. 
       FIG. 2  is a schematic diagram of a prior art fluid flow regulator  200  that uses non-flowing orifice damping. The regulator  200  includes a fluid at  202  and a fluid at  204 . The fluid at  202  is fluidically connected to a fluid path  206 , and the fluid at  204  is fluidically connected to a fluid path  208 . 
     The inlet fluid path  206  is fluidically connected to the outlet fluid path  208  through a bypass valve  210 . The bypass valve  210  includes a number of ports (not shown) that fluidically connects the inlet fluid path  230  to the outlet fluid path  240 . The bypass valve  210  exhibits a regulator velocity, generally represented by the arrow  212 . A damping orifice  220  restricts fluid flow from the bypass valve  210  to the fluid outlet  204  along the outlet fluid path  208 . In some embodiments, the fluid flow regulator  200  can also include a damping orifice  222  that restricts fluid flow from the fluid inlet  202  to the bypass valve  210 . 
     Non-flowing orifice damping exhibits less temperature sensitivity than valves using laminar leak path damping. However, non-flowing orifice damping is proportional to the square of the regulator velocity  212 . As a result, the orifice provides little to no damping when the bypass valve  210  is stationary (e.g., valve velocity  212  is equal to zero), but can over-damp the bypass valve  210  during large disturbances. 
     At low regulator velocities, low flow is induced across the damping orifices  220  and  222 . The induced flow across the damping orifices  220  and  222  results in a differential pressure drop that is proportional to the square of flow (e.g., non-linear). In examples in which the orifices  220 ,  222  are appropriately sized (e.g., greater than about 0.020 inches diameter), the differential pressures generated by low regulator velocities may be negligible, resulting in little to no damping of the bypass valve  210 . In addition, orifice flow is proportional to the square root of fuel specific gravity, and is substantially independent of fuel viscosity. For example, typical aircraft fuels and temperature ranges can result in fuel specific gravity from 0.873 (−65 F JetA) to 0.712 (300 F JetA), resulting in a damping variation due to temperature of approximately 1.1×. 
     In aircraft applications, space and weight can be limited commodities. Use of the pressure regulator  200  of  FIG. 2  in such examples may allow high-frequency pressure oscillations in the fuel to go substantially undamped across the valve  210 . For example, the operations of fuel injectors downstream of the pressure regulator  200  may introduce oscillations that can back-propagate and cause problems with equipment upstream from the pressure regulator  200  (e.g., noisy sensor readings, damage to fuel pumps). In another example, oscillations introduced upstream of the pressure regulator  200  (e.g., by fuel pumps, vibration from the engine) can propagate to and interfere with the function of equipment downstream from the pressure regulator (e.g., fuel injectors). 
       FIG. 3  is a schematic diagram of an example fluid flow regulator  300 . The regulator  300  includes a fluid at  302  and a fluid at  304 . The fluid at  302  is fluidically connected to an inlet fluid path  306 , and the fluid at  304  is fluidically connected to an outlet fluid path  308 . 
     A fluid with a flow to be regulated is provided at the fluid inlet  302  of the inlet fluid path  306 . The inlet fluid path  306  is fluidically connected to the outlet fluid path  308  through a bypass valve  310 . The bypass valve  310  includes a number of ports (not shown) that fluidically connects the inlet fluid path  330  to the outlet fluid path  340 . A spring  311  urges the valve  310  toward a position that restricts or blocks fluid flow between the inlet fluid path  330  and the outlet fluid path  340 . The valve  310  is responsive to changes in pressure differential  313  and  314  across it. In general, as pressure at the inlet fluid path  306  decreases, the bias force of the spring  311  urges the valve  310  toward a position that decreases allowable flow area between inlet fluid path  330  and the outlet fluid path  340 . Decreasing the allowable flow area of bypass valve  310  also decreases the rate of flow from the inlet fluid path  330  to the outlet fluid path  340 . The flow rate remains approximately at a specified level even though pressure at the valve  310  varies. 
     The bypass valve  310  exhibits a regulator velocity, generally represented by the arrow  312 . A damping orifice  320  restricts fluid flow from the bypass valve  310  to the fluid outlet  304  along the outlet fluid path  308 . In some embodiments, the fluid flow regulator  300  can also include a damping orifice  322  that restricts fluid flow from the fluid inlet  302  to the bypass valve  310 . 
     A bypass fluid path  330  fluidically connects the inlet fluid path  306  to the outlet fluid path  308  in parallel with the bypass valve  310 . The bypass flow path  330  includes a minimum flow orifice  332  that restricts fluid flow from the fluid inlet path  306  to the fluid outlet path  308 . In some embodiments, the minimum flow orifice  332  can be sized based on a predetermined minimum fluid flow. 
     The regulator  300  maintains the advantage of temperature insensitivity similar to the non-flowing orifice damping design of the example regulator  200  of  FIG. 2 , but also provides linear damping similar to that provided by the example regulator  100  of  FIG. 1 . By using the configuration of the example regulator  300 , the regulator has the same damping when stationary as during large transients. In the example regulator  300 , the minimum flow orifice  332  converts the damping orifices  322  and  320  of the bypass valve  310  from non-flowing orifices to flowing orifices. As a result, damping of the bypass valve  310  becomes less amplitude dependent, yet leakage is not impacted. 
     Given the flowing orifice configuration of the example regulator  300 , there exists a continuous, non-zero flow across the damping orifices of the bypass valve  310  and the minimum flow orifice  332 . The continuous flow across the damping orifices of the bypass valve  310  results in a differential pressure drop induced across the damping orifices, which serves as a mechanism for damping at low valve velocities ( 312 ) as well as high valve velocities ( 312 ). Similar to the non-flowing orifice configuration of the example regulator  200 , the flowing orifice configuration of the regulator  300  is insensitive to fluid viscosity variation due to temperature changes. 
     Additionally, the flowing orifice configuration of the example regulator  300  has a larger diameter damping orifice(s) than is appropriate to provide the similar levels of bypass damping in regulators that implement a non-flowing orifice configuration. In some implementations, the configuration of the regulator  300  can provide a number of advantages over the damping schemes implemented by the regulators  100  and  200 . For example, the relatively larger damping orifices of the regulator  300  can provide relatively improved contamination resistance. In another example, the regulator  300  can exhibit relatively reduced leakage sensitivity since small amounts of bypass leakage, which is typically temperature dependent, has been known to bias the pressure differential setting of bypass valves, resulting in fuel flow errors. The configuration of the regulator  300  reduces this leakage sensitivity. In another example, some other regulator designs require the use of check valves in parallel to the relatively smaller bypass orifices, resulting in added weight and cost. Such check valves are not needed in the configuration of the regulator  300 . 
       FIG. 4  is a schematic diagram of an example fluid delivery system  400  that includes fluid flow regulator damping, such as that provided by the example regulator  300  of  FIG. 3 . The system  400  includes a bypass valve  410 , a metering valve  430 , and a pressurizing valve  450  (e.g., pressure regulator). In some implementations, the system  400  can regulate fuel flow to an aircraft engine. In general, a fluid  402  (e.g., fuel) is provided at a fluid inlet  404 . The fluid flows to a meter inlet  432  of the metering valve  430 , and out from a meter outlet  434  to a pressurizing valve inlet  452  of the pressurizing valve  450 . 
     The metering valve  430  is responsive to an external servo valve (not shown). The servovalve is coupled to actuate plunger  433 , metering valve plunger position is communicated to an electronic control via a position feedback device  431 . As the metering valve moves, a fluid path between a valve inlet  480  and a valve outlet  482  is selectively opened and closed. In use, the metering valve  430  can be actuated to adjust a rate of fluid flow at the valve outlet  482 . 
     The bypass valve  410  includes a collection of ports  411 . The bypass valve is actuated in response to the difference in fluid pressure developed in fluid conduit  490  and  495 . Fluid conduit  490  can be described as fluid pressure in a fluid path between a minimum flow orifice  470  and a damping orifice  472   b . Fluid conduit  495  can be described as fluid pressure in a fluid path between a minimum flow orifice  470  and a damping orifice  472   a . When force exerted on the bypass valve  410  by the pressure differential in fluid conduit  490  and  495  is not sufficient to overcome the force provided by a spring  412 , the bypass valve closes and restricts flow of the fluid  402  to an outlet  420 . As the force exerted on the bypass valve  410  by the pressure differential in the fluid conduit  490  and  495  exceeds the opposing force, the valve  410  opens and allows flow to pass to the outlet  420 . 
     The pressurizing valve  450  includes a spring  458  and plunger  459 . The spring  458  and a force provided by the pressure of the fluid  460  applied at the input  456  biases the plunger  459  into the fluid flow between the valve outlet  482  and the outlet  454 . The pressurizing valve  450  regulates the pressure of the fluid  402  at an inlet  452  in response to the pressure of a fluid  460  applied at an input  456  and a spring force  458 . In some embodiments, the bypass valve  410  can be the bypass valve  310 . 
     In use, the bypass valve  410  maintains a substantially constant differential pressure across the metering window of the metering valve  430 . The metering valve  430  holds a metering port window that corresponds to the desired flow of the fluid  454  (e.g., a desired engine burn flow) in response to an input signal (e.g., from an engine controller or pilot input). The pressurizing valve  450  maintains at least a predetermined minimum fluidic pressure used to provide fluidic force margins for the metering valve  430  and internal or external actuation systems. 
     The example system  400  also includes the minimum flow orifice  470 , the damping orifice  472   a , and a damping orifice  472   b . The orifices  470 ,  472   a , and  472   b  restrict a bypass fluid flow path that bypasses the metering valve  430 . The bypass fluid flow path extends from the inlet  404  and/or the valve inlet  480 , through a damping orifice  472   b , along the fluid conduit  490 , through the minimum flow orifice  470 , along fluid conduit  495 , through a damping orifice  472   a , to the valve outlet  482 . The minimum flow orifice  470 , which in some embodiments can be the minimum flow orifice  332  of  FIG. 3 , can be adjusted to calibrate for low fluid (e.g., fuel) flow requirements. In some embodiments, the minimum flow orifice  470  can be sized based on a predetermined minimum fluid flow to be passed through the bypass fluid flow path. In some embodiments, the minimum flow orifice  470  can be an adjustable orifice. 
     In use, the minimum flow orifice  470  continuously permits a specified amount of the fluid  402  to flow along a fluid path extending from the valve inlet  480  to the valve outlet  482 , bypassing the fluid path provided by the metering valve  430 . The two damping orifices  472   a  and  472   b , which in some embodiments can be the damping orifices  320  and  322 , are positioned in a series circuit with the minimum flow orifice  470 . As such, all the fluid  402  that is passed by the minimum flow orifice  470  also passes through the damping orifices  472   a  and  472   b . In some embodiments, the fluid flow rate at the valve outlet  482  can be the sum of the minimum fluid flow through the minimum flow orifice  470  and the regulated fluid flow rate through the metering valve  430 . 
     The portion of the fluid  402  bypassing the metering valve  430  flows from the fluid inlet  404  (and the valve inlet  480 , which is at the same pressure as the fluid inlet  402 ) through the damping orifice  472   b , to a fluid conduit  490 , to the minimum flow orifice  470 , through the damping orifice  472   a , and to the valve outlet  482 . The flow remains substantially continuous at a specified flow rate, except for displacement flow provided by the bypass valve  410  which will add to or subtract from the described flow path. In some implementations, displacement flow from the bypass valve  410  can be relatively low compared to metering flow levels, and in cases can be ignored. 
       FIG. 5  is a schematic diagram of an example fluid delivery system  500  that includes fluid flow regulator damping. The system  500  is similar to the example system  400  of  FIG. 4 , except that the two damping orifices  472   a  and  472   b  are reduced to a single damping orifice  572  along the bypass fluid flow path. Given this architecture, the fluid  402  flows from the fluid inlet  404  (and the valve inlet  480 , which is at the same pressure as the fluid inlet  404 ) through the fluid conduit  490 , to the minimum flow orifice  470 , and to the valve outlet  482 . In some implementations, the configuration shown in  FIG. 5  may be used in an engine fuel delivery application. 
     In some implementations, the configuration of the system  500  simplifies the configuration of the system  400 , eliminating the need to install and account for tolerance variations that may be associated with the damping orifice  472   b . In some implementations, the configuration of the system  500  can cause the minimum flow orifice  470  to provide a protective filtering benefit to the damping orifice  572 . In some embodiments, the fluid flow rate at the valve outlet  482  can be the sum of the minimum fluid flow through the minimum flow orifice  470  and the regulated fluid flow rate through the metering valve  430 . 
       FIG. 6  is a schematic diagram of an example fluid delivery system  600  that includes fluid flow regulator damping. The system  600  is similar to the example system  500  of  FIG. 5 , except that a minimum flow circuit  602  fluidically connects the valve inlet  480  to the valve outlet  482  in parallel with the metering valve  430  and the bypass fluid flow path  490 . A minimum flow orifice  670  is included in the minimum flow circuit  602 . Compared to the system  500 , the system  600  also replaces the minimum flow orifice  470  of the system  500  with a flow limiter orifice  610 . In some implementations, the configuration shown in  FIG. 6  may be used in an engine fuel delivery application. In some embodiments, the minimum flow orifice  670  can be an adjustable flow orifice. 
     Given this architecture, the fluid  402  flows from the fluid inlet  404  (and the valve inlet  480 , which is at the same pressure as the fluid inlet  404 ) through the fluid conduit  490 , to the flow limiter orifice  610 , through flow conduit  495 , through the damping orifice  572 , and to the valve outlet  482 , and the minimum flow circuit flows from the valve inlet  480 , through the minimum flow orifice  670 , to the valve outlet  482 . In some embodiments, the fluid flow rate at the valve outlet  482  can be the sum of the minimum fluid flow through the minimum flow orifice  670  and the damping flow circuit  490  and the regulated fluid flow rate through the metering valve  430 . In some implementations, the configuration of the system  600  can cause calibration of the minimum flow orifice  670  to have little or no impact upon the damping performance of the bypass system. 
       FIG. 7  is a schematic diagram of an example fluid delivery system  700  that includes fluid flow regulator damping. The system  700  is similar to the example system  600  of  FIG. 6 , except that flow conduit  490  includes additional features to prevent icing of the damping flow circuit  490 , such as a wash screen assembly  710  and a fuel heating element  720 . The wash screen assembly  710  is resistant to heavy contamination as well as large quantities of ice, and the fuel heating element  720  provides fuel temperatures above freezing to preventing ice crystals from building up on the critical features of the damping circuit. In some implementations, the configuration shown in  FIG. 7  may be used in an engine fuel delivery application. In some embodiments, the minimum flow orifice  670  can be an adjustable flow orifice. 
     Given this architecture, the fluid  402  flows from the fluid inlet  404  through wash screen  710 , through the heating element  720 , thru the fluid conduit  490 , to the flow limiter orifice  610 , through flow conduit  495 , through the damping orifice  572 , and to the valve outlet  482 , and the minimum flow circuit flows from the valve inlet  480 , through the minimum flow orifice  670 , to the valve outlet  482 . In some embodiments, the fluid flow rate at the valve outlet  482  can be the sum of the minimum fluid flow through the minimum flow orifice  670  and the damping flow circuit  490  and the regulated fluid flow rate through the metering valve  430 . In some implementations, the configuration of the system  700  can cause calibration of the minimum flow orifice  670  to have no impact upon the damping performance of the bypass system. 
     The architecture of  FIG. 7  provides the greatest protection for the damping circuit via the wash screen assembly  710  and the heating element  720 . The wash screen assembly  710  is positioned in flow path  402  such that the large majority of fluid flow passes down the center of the wash screen assembly  710  and through to the valve inlet  480 . Only a small percentage of flow passes to conduit  490 , thereby providing a continuous washing of the filter media to prevent contamination and ice buildup. The heating element  720  is exposed only to the damping flow circuit flow, and therefore can be sized accordingly. The heating element  720  may be of various types, including but not limited to electrical, fluid heat transfer, or mechanical. In some embodiments, the fluid conduit  490  may be split to provide washed and/or heated fluid to other features within the system  700 . 
     Although a few implementations have been described in detail above, other modifications are possible. For example, logic flows do not require the particular order described, or sequential order, to achieve desirable results. In addition, other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.