Hydraulic fluid heat dissipation control assembly and method

There is provided in an embodiment a hydraulic fluid heat dissipation control assembly for an aircraft hydraulic system. The hydraulic fluid heat dissipation control assembly has one or more heat exchangers. The hydraulic fluid heat dissipation control assembly further has at least one flow control element coupled to the one or more heat exchangers to control flow and heat dissipation of a hydraulic fluid. There is also provided a method of controlling heat dissipation of a hydraulic fluid in an aircraft hydraulic system using the hydraulic fluid heat dissipation control assembly disclosed herein.

BACKGROUND

1) Field of the Disclosure

The disclosure relates generally to assemblies and methods for hydraulic systems, and more specifically, to assemblies and methods for controlling hydraulic fluid temperature in hydraulic systems, such as an aircraft hydraulic system.

2) Description of Related Art

Aircraft hydraulic systems may be used to provide power for various operating components of an aircraft, such as wing flaps, thrust reversers, flight control surfaces, and landing gear mechanisms. Large, multi-engine aircraft may have several independent hydraulic systems. For example, two engine aircraft may have three hydraulic systems and four engine aircraft may have four hydraulic systems. Such aircraft hydraulic systems typically include engine driven or electrically driven pump devices mounted on each of the multiple engines. The pump devices pump hydraulic fluid through the aircraft hydraulic system at a high pressure. Aircraft typically operate at a pressure of 3000 psi (pounds per square inch), and some military aircraft and other aircraft may operate at a pressure of 5000 psi. Moreover, aircraft hydraulic systems for large, multi-engine aircraft may generate excess heat from the pump devices, such as in hot weather operations or conditions, which, in turn, may increase the temperature of the hydraulic fluid. Further, cold weather operations or conditions may decrease the temperature of the hydraulic fluid. Overheated hydraulic fluid, as well as hydraulic fluid that is not warm enough, may limit or restrict operation of the aircraft hydraulic system.

Known devices and methods exist for controlling the hydraulic fluid temperature in aircraft hydraulic systems. One such known device and method includes use and installation of a single fixed effect heat exchanger in an aircraft hydraulic system, such as, for example, in an aircraft fuel tank. However, for cold weather operations or conditions that require the hydraulic fluid be warmed up, use of such a heat exchanger may remove too much heat and may result in a cold hydraulic fluid that may be too cold to satisfy the required performance. Thus, operational restrictions and/or additional warm-up procedures may be required for cold weather operations. In some cases, design changes to the aircraft hydraulic systems may be required to up-size the hydraulic tubing and components in order to meet the requirement of hydraulic performance in cold weather conditions. Such increased size of the hydraulic tubing and components, in turn, may increase the overall weight of the aircraft which may result in a weight penalty and increased fuel costs.

Another known device and method includes use and installation of one or more thermostat control valves in an aircraft hydraulic system. However, such known thermostat control valves may require a thermal actuator which may be expensive, unreliable and may require a long lead time to develop. Moreover, such known thermostat control valves may not be capable of controlling heat dissipation based on a running condition of the pump device.

Accordingly, there is a need in the art for improved devices, assemblies, and methods for hydraulic fluid temperature or heat dissipation control in aircraft hydraulic systems that provide advantages over known devices, assemblies, and methods.

SUMMARY

This need for improved devices, assemblies, and methods for hydraulic fluid temperature or heat dissipation control in aircraft hydraulic systems is satisfied. As discussed in the below detailed description, embodiments of assemblies and methods may provide significant advantages over existing devices, assemblies, and methods.

In an embodiment of the disclosure, there is provided a hydraulic fluid heat dissipation control assembly for an aircraft hydraulic system. The hydraulic fluid heat dissipation control assembly has one or more heat exchangers. The hydraulic fluid heat dissipation control assembly further has at least one flow control element coupled to the one or more heat exchangers to control flow and heat dissipation of a hydraulic fluid.

In another embodiment of the disclosure, there is provided an aircraft having an aircraft hydraulic system with a hydraulic fluid heat dissipation control assembly. The aircraft comprises a fuselage, a pair of wings operatively coupled to the fuselage, and one or more aircraft hydraulic systems disposed within at least one of the fuselage and the pair of wings. Each aircraft hydraulic system comprises a hydraulic fluid heat dissipation control assembly. The hydraulic fluid heat dissipation control assembly comprises at least one fluid flow line. The hydraulic fluid heat dissipation control assembly further comprises one or more pump devices coupled to the at least one fluid flow line. The hydraulic fluid heat dissipation control assembly further comprises one or more heat exchangers coupled to the at least one fluid flow line. The hydraulic fluid heat dissipation control assembly further comprises at least one pressure control valve coupled to the at least one fluid flow line to control flow and heat dissipation of a hydraulic fluid from the one or more pump devices through the at least one fluid flow line and through the one or more heat exchangers in order to obtain a heat dissipation controlled hydraulic fluid which then flows to a return flow line or to a hydraulic fluid reservoir both located in the aircraft hydraulic system.

In another embodiment of the disclosure, there is provided a method of controlling heat dissipation of a hydraulic fluid in an aircraft hydraulic system. The method comprises installing a hydraulic fluid heat dissipation control assembly in an aircraft hydraulic system. The hydraulic fluid heat dissipation control assembly comprises at least one fluid flow line positioned in the aircraft hydraulic system. The hydraulic fluid heat dissipation control assembly further comprises one or more pump devices coupled to the at least one fluid flow line. The hydraulic fluid heat dissipation control assembly further comprises one or more heat exchangers coupled to the at least one fluid flow line. The hydraulic fluid heat dissipation control assembly further comprises at least one flow control element coupled to the at least one fluid flow line. The method further comprises sensing with the at least one flow control element a pressure differential across one of the one or more heat exchangers. The method further comprises controlling with the at least one flow control element the flow of the hydraulic fluid through the one or more heat exchangers so as to vary heat dissipation from the aircraft hydraulic system and so as to obtain a heat dissipation controlled hydraulic fluid. The method further comprises flowing the heat dissipation controlled hydraulic fluid to one of at least a return flow line or to a hydraulic fluid reservoir both in the aircraft hydraulic system.

DETAILED DESCRIPTION

Disclosed embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all of the disclosed embodiments are shown. Indeed, several different embodiments may be provided and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the disclosure to those skilled in the art.

Now referring to the Figures,FIG. 1is an illustration of a perspective view of an aircraft10with an aircraft hydraulic system26incorporating an exemplary embodiment of a hydraulic fluid heat dissipation control assembly28of the disclosure. As shown inFIG. 1, the aircraft10comprises a fuselage12, a nose14, a cockpit16, a pair of wings18operatively coupled to the fuselage12, one or more engines20, a vertical tail portion22, and horizontal tail portions24. Although the aircraft10shown inFIG. 1is generally representative of a commercial passenger aircraft having a hydraulic fluid heat dissipation control assembly28, the teachings of the disclosed embodiments may be applied to other passenger aircraft, cargo aircraft, military aircraft, and other types of aircraft or aerial vehicles.

FIG. 2is an illustration of a schematic diagram of one of the embodiments of a hydraulic fluid heat dissipation control assembly28, such as in the form of a hydraulic fluid heat dissipation control assembly28a, for an aircraft hydraulic system26.FIG. 4is an illustration of a schematic diagram of another one of the embodiments of a hydraulic fluid heat dissipation control assembly28, such as in the form of a hydraulic fluid heat dissipation control assembly28b, for an aircraft hydraulic system26.FIG. 5is an illustration of a schematic diagram of yet another one of the embodiments of a hydraulic fluid heat dissipation control assembly28, such as in the form of a hydraulic fluid heat dissipation control assembly28c, for an aircraft hydraulic system26.

As shown inFIGS. 2, 4, and 5, there is provided a hydraulic fluid heat dissipation control assembly28for an aircraft hydraulic system26. The hydraulic fluid heat dissipation control assembly28may comprise at least one fluid flow line30(seeFIGS. 2, 4, 5) positioned in an aircraft hydraulic system26. The at least one fluid flow line30preferably comprises a case drain flow line31(seeFIGS. 2, 4, 5). The at least one fluid flow line30, in the form of case drain line31, carries hydraulic fluid32(seeFIGS. 2, 4, 5) from one or more pump devices34(seeFIGS. 2, 4, 5) to a return line52(seeFIGS. 2, 4, 5) and to a hydraulic fluid reservoir54(seeFIGS. 2, 4, 5). The case drain flow line31takes away heat from the one or more pump devices34. The temperature of the hydraulic fluid32in the case drain flow line31may be 20° F. to 50° F. higher than the temperature of the hydraulic fluid entering the pump device34from the hydraulic fluid reservoir54.

The hydraulic fluid heat dissipation control assembly28may further comprise one or more pump devices34(seeFIGS. 2, 4, 5) coupled to the at least one fluid flow line30. The one or more pump devices34may comprise, for example, one or more primary pump devices36(seeFIGS. 4, 5), one or more demand pump devices38(seeFIGS. 4, 5), or another suitable pump device34. Preferably, the one or more pump devices34are hydraulic pump devices or another suitable type of pump device.FIG. 2shows one pump device34which may comprise either one primary pump device36or one demand pump device38. Alternatively, the hydraulic fluid heat dissipation control assembly28ofFIG. 2may comprise two pump devices34, such as one primary pump device36and one demand pump device38.FIGS. 4 and 5show two pump devices34comprising one primary pump device36and one demand pump device38. The one or more pump devices34may be powered or driven by the one or more engines20(seeFIG. 1), may be electrically powered or driven, or may be powered or driven by another suitable source or means.

As shown inFIGS. 2, 4, and 5, the hydraulic fluid heat dissipation control assembly28comprises one or more heat exchangers40(HX). The one or more heat exchangers40may be coupled to the at least one fluid flow line30. The one or more heat exchangers40are preferably located in one or more fuel tanks42, for example, either together in one fuel tank42or separately in two or more fuel tanks42. In one embodiment, as shown inFIG. 2, the hydraulic fluid heat dissipation control assembly28may have two (2) heat exchangers40(HX), such as heat exchanger40aand heat exchanger40bpositioned in parallel to each other in one fuel tank42.

In another embodiment, as shown inFIG. 5, the hydraulic fluid heat dissipation control assembly28may have two heat exchangers40(HX), such as heat exchanger40aand heat exchanger40b, positioned in parallel to each other with one heat exchanger40alocated in one fuel tank42, such as fuel tank42a, and with another heat exchanger40blocated in another fuel tank42, such as fuel tank42b, which is separate from fuel tank42a.

In another embodiment, as shown inFIG. 4, the hydraulic fluid heat dissipation control assembly28may have three heat exchangers40(HX), such as heat exchanger40a, heat exchanger40b, and heat exchanger40c, with two of the three heat exchangers40positioned in parallel to each other. As shown inFIG. 4, heat exchanger40aand heat exchanger40bare positioned in parallel to each other in one fuel tank42, such as fuel tank42a, and heat exchanger40cis located in another separate fuel tank42, such as fuel tank42b, separate from fuel tank42a. Preferably, the heat exchangers40used are the same or similar types of known heat exchangers used in aircraft hydraulic systems.

As shown inFIGS. 2, 4, and 5, the hydraulic fluid heat dissipation control assembly28further comprises at least one flow control element44coupled to the one or more heat exchangers40to control flow and heat dissipation of a hydraulic fluid50(seeFIGS. 2, 4, 5). Preferably, the at least one flow control element44comprises a pressure control valve46(seeFIGS. 2, 4, 5).FIGS. 2, 4, and 5each show one flow control element44in the form of a pressure control valve46. However, additional flow control elements44may also be used. Preferably, for additional heat exchangers40greater than three heat exchangers, an additional flow control element44, such as in the form of pressure control valve46, may be used. Preferably, the pressure control valves46used are suitable known pressure control valves.

The at least one flow control element44, such as in the form of pressure control valve46, preferably controls the flow and heat dissipation of the hydraulic fluid32(seeFIGS. 2, 4, 5) that flows from the one or more pump devices34through the at least one fluid flow line30and through the one or more heat exchangers40in order to obtain a heat dissipation controlled hydraulic fluid50(seeFIGS. 2, 4, 5). The heat dissipation controlled hydraulic fluid50may then flow to a return flow line52(seeFIGS. 2, 4, 5) or to a hydraulic fluid reservoir54(seeFIGS. 2, 4, 5). The return flow line52and the hydraulic fluid reservoir54are both located in the aircraft hydraulic system26. The hydraulic fluid reservoir54is preferably at a low pressure, such as 50 psi (pounds per square inch).

As shown inFIGS. 2, 4 and 5, the hydraulic fluid heat dissipation control assembly28may further comprise a pressure line56coupled to the return flow line52via the one or more pump devices34. The pressure line56is preferably at a high pressure, such as 3000 psi (pounds per square inch) or 5000 psi. The hydraulic fluid heat dissipation control assembly28may further comprise one or more filters58(seeFIGS. 2, 4, 5) for filtering and cleaning the hydraulic fluid32and removing impurities in the aircraft hydraulic system26and in the hydraulic fluid reservoir54. Thus, each aircraft hydraulic system26preferably has one or more pump devices34, and more preferably has a primary pump device36and a demand pump device38. Each pump device34has ports for the return flow line52(also referred to as a supply flow line), the pressure line56, and the case drain flow line31.

Embodiments of the hydraulic fluid heat dissipation control assembly28disclosed herein advantageously control heat dissipation of the hydraulic fluid32in the aircraft hydraulic system26, in order to condition the hydraulic fluid32to maintain an optimum hydraulic fluid temperature, such that the hydraulic fluid32is preferably not overheated for hot day operations or conditions, and such that the hydraulic fluid32preferably retains heat to maintain a warmer hydraulic fluid temperature in the aircraft hydraulic system26, so as to ensure adequate hydraulic performance for cold day operations or conditions. Thus, the hydraulic fluid heat dissipation control assembly28disclosed herein advantageously helps to maintain an ideal hydraulic fluid temperature range for both hot day and cold day operations or conditions.

As shown inFIG. 2, in one embodiment, the hydraulic fluid heat dissipation control assembly28, such as hydraulic fluid heat dissipation control assembly28a, has one flow control element44, such as in the form of pressure control valve46, and has two heat exchangers40, such as heat exchanger40a(HX) and heat exchanger40b(HX). The two heat exchangers40a,40b, are positioned in parallel to each other in a fuel tank42. The hydraulic fluid heat dissipation control assembly28preferably has one flow control element, such as in the form of pressure control valve46, positioned in line with one of the two heat exchangers40that are positioned in parallel to each other. As shown inFIG. 2, the flow control element44, such as in the form of pressure control valve46, is positioned in line with heat exchanger40b. The pressure control valve46preferably senses a pressure differential across the filter58(seeFIG. 2) and the two heat exchangers40a,40bin order to control flow of the hydraulic fluid32through the two heat exchangers40a,40b, so as to control heat dissipation from the aircraft hydraulic system26. The pressure control valve46controls the connection and disconnection of the heat exchanger40bthat is in line with the pressure control valve46, and the other heat exchanger40ais preferably open. The pressure differential sensed by the pressure control valve46may vary with a temperature of the hydraulic fluid32.

FIG. 6is an illustration of a heat exchanger pressure drop graph82showing pressure drop psid (pounds per square inch differential) versus hydraulic fluid temperature in ° F. (degrees Fahrenheit).FIG. 6shows a hydraulic fluid temperature-pressure drop measurements plot line84indicating that as the hydraulic fluid temperature increases, the pressure drop decreases, and as the hydraulic fluid temperature decreases, the pressure drop increases. For example, as shown inFIG. 6, at a hydraulic fluid temperature of about 50° F., the pressure drop is about 50 psid, whereas at a hydraulic fluid temperature of 100° F., the pressure drop is about 25 psid.

FIG. 7is an illustration of a heat exchanger efficiency graph86showing efficiency in % (percent) of the heat exchanger versus hydraulic fluid flow rate in gpm (gallons per minute).FIG. 7shows a hydraulic fluid flow rate-efficiency measurements plot line88indicating that as the hydraulic fluid flow rate increases, the efficiency of the heat exchanger decreases, and as the hydraulic fluid flow rate decreases, the heat exchanger efficiency increases. For example, as shown inFIG. 7, at a hydraulic fluid flow rate of about 1.5 gpm, the efficiency of the heat exchanger is about 58%, whereas at a hydraulic fluid flow rate of about 6.5 gpm, the efficiency of the heat exchanger is about 25%.

Due to the hydraulic fluid flow rate-efficiency measurements plot line88shown inFIG. 7, the flow control element44(seeFIG. 2), such as in the form of pressure control valve46(seeFIG. 2), has an open-close performance related to the hydraulic fluid temperature-pressure drop measurements plot line84shown inFIG. 6. The state of being opened or closed of the flow control element44, such as in the form of pressure control valve46, may result in a distinct variation of heat dissipation from the heat exchangers40into the fuel tank42(seeFIG. 2). The heat exchanger efficiency may be calculated with the following formula: Efficiency=(Tinminus Tout)/(Tinminus Tfuel), where Tinis the hydraulic fluid temperature at the heat exchanger inlet or entrance, Toutis the hydraulic fluid temperature at the heat exchanger outlet or exit, and Tfuelis the fuel temperature.

Based on the heat exchanger characteristics shown inFIGS. 6 and 7,FIG. 3shows an illustration of a pressure control valve opening graph70indicating (pressure control) valve opening in % (percent) versus hydraulic fluid temperature in ° F. (degrees Fahrenheit).FIG. 3shows a nonlinear characteristic72representing the pressure control valve46(seeFIG. 2) opening and closing in relation to the heat exchangers40(seeFIG. 2) at a hydraulic fluid temperature in a range of about 70° F. to about 120° F. and a pressure control valve opening from 0% to 100%. Arrow80, as shown inFIG. 3, indicates a temperature increase or heating up of the hydraulic fluid from 70° F. to about 120° F. Such temperature increase results in a pressure decrease or drop to allow the pressure control valve46(seeFIG. 2) to open. When the temperature is increased, and the pressure drop is decreased, a spring48(seeFIG. 2) in the pressure control valve46(seeFIG. 2) overcomes a pressure to open the pressure control valve46, so that the heat exchanger40b(seeFIG. 2) is connected and in use. Arrow74, as shown inFIG. 3, indicates a (pressure control) valve opening increase from 0% to 100%. Such (pressure control) valve opening results in both heat exchangers40being connected and in use. Arrow76, as shown inFIG. 3, indicates a temperature decrease or cooling of the hydraulic fluid from 120° F. to about 70° F. Such temperature decrease results in an increased pressure differential (across the filter58(seeFIG. 2) and the heat exchangers40a,40b(seeFIG. 2)), which overcomes the spring48in the pressure control valve46to close the pressure control valve46so the heat exchanger40bis disconnected and not in use. Arrow78, as shown inFIG. 3, indicates a (pressure control) valve opening decrease from 100% to 0%. Such (pressure control) valve opening decrease results in one heat exchanger40abeing preferably connected and in use and the other heat exchanger40bbeing preferably disconnected and not in use.

As shown inFIG. 4, in another embodiment, the hydraulic fluid heat dissipation control assembly28, such as hydraulic fluid heat dissipation control assembly28b, has one flow control element44, such as in the form of pressure control valve46, and has three heat exchangers40, such as heat exchanger40a(HX), heat exchanger40b(HX), and heat exchanger40c(HX). The pressure control valve46senses a pressure differential between a case drain pressure (P)33(seeFIG. 4) of a demand pump38(seeFIG. 4) and a return flow line pressure (P)53(seeFIG. 4), in order to control flow of the hydraulic fluid32through one or more of the three heat exchangers40and to control heat dissipation from the aircraft hydraulic system26. In particular, as shown inFIG. 4, the flow control element44, such as in the form of pressure control valve46, may also sense other components in the case drain flow line31, including sensing the pressure differential across the filter58band the heat exchanger40cof the demand pump device38, so the state of being opened or closed of the pressure control valve46is directly associated with a running condition of the demand pump device38, for example, when the demand pump device38is “on” or “off”. As a result, the pump condition with only the primary pump device36(seeFIG. 4) running preferably has one heat exchanger40, such as heat exchanger40aor heat exchanger40b, in effect. Thus, when the one or more pump devices34comprise one or more primary pump devices36, and when only the one or more primary pump devices36are running, only one of the three heat exchangers40is operational. Further, the condition with both the primary pump device36and the demand pump device38running preferably has three heat exchangers40, such as heat exchangers40a,40b,40c, in effect. Thus, when the one or more pump devices34comprise one or more primary pump devices36and one or more demand pump devices38, and when both of the one or more primary pump devices36and the one or more demand pump devices38are running, all three of the heat exchangers40are operational. Finally, when the one or more pump devices34comprise one or more demand pump devices38, the pressure differential varies with a pump running condition of the one or more demand pump devices38.

As shown inFIG. 5, in another embodiment of the hydraulic fluid heat dissipation control assembly28, such as hydraulic fluid heat dissipation control assembly28c, such embodiment shown inFIG. 5is similar to the embodiment of the hydraulic fluid heat dissipation control assembly28, such as hydraulic fluid heat dissipation control assembly28b, shown inFIG. 4, except that the flow control element44, such as in the form of pressure control valve46, may be positioned or placed in a by-pass path60(seeFIG. 5), so the pump condition with the primary pump device36running preferably has no heat exchanger40in effect, that is, neither heat exchanger40a(seeFIG. 5) nor heat exchanger40b(seeFIG. 5). Thus, when the one or more pump devices34comprise one or more primary pump devices36, and when the hydraulic fluid heat dissipation control assembly28has one flow control element44, such as pressure control valve46, positioned in the by-pass path60, a pump running condition of each of the one or more primary pump devices36has none of the two or more heat exchangers40in operation. The embodiment shown inFIG. 5preferably benefits cold day operations in which additional heat may be required to warm up the hydraulic fluid of the aircraft hydraulic system26.

FIG. 8is an illustration of a total heat dissipation from heat exchangers graph90showing heat dissipation in BTU/min (British thermal units per minute) versus hydraulic fluid flow rate in gpm (gallons per minute).FIG. 8shows a hydraulic fluid flow passing through two heat exchangers-heat dissipation measurements plot line92and a hydraulic fluid flow passing through one heat exchanger-heat dissipation measurements plot line94. The measurements for the hydraulic fluid flow passing through two heat exchangers-heat dissipation measurements plot line92and the hydraulic fluid flow passing through one heat exchanger-heat dissipation measurements plot line94were taken at a hydraulic fluid flow temperature of 220° F. (degrees Fahrenheit), a fuel temperature of 120° F. (degrees Fahrenheit), and a hydraulic fluid flow rate equally distributed on two heat exchangers positioned in parallel to each other. As shown inFIG. 8, at a hydraulic fluid flow rate of 1 gpm, the heat dissipation of the hydraulic fluid flow passing through one heat exchanger and the hydraulic fluid flow passing through two heat exchangers is the same at 200 BTU/min. Thus, there appears to be no difference between having one heat exchanger or two heat exchangers at a hydraulic fluid flow rate of 1 gpm. As further shown inFIG. 8, at a hydraulic fluid flow rate of 2 gpm, the heat dissipation of the hydraulic fluid flow passing through one heat exchanger is slightly less than 400 BTU/min, and the hydraulic fluid flow passing through two heat exchangers is slightly greater than 400 BTU/min. Thus, there starts to show a slight difference between having one heat exchanger or two heat exchangers at a hydraulic fluid flow rate of 2 gpm. As further shown inFIG. 8, at a hydraulic fluid flow rate of 3 gpm, the heat dissipation of the hydraulic fluid flow passing through one heat exchanger is about 500 BTU/min, and the hydraulic fluid flow passing through two heat exchangers is about 600 BTU/min. There, a benefit is shown with having two heat exchangers over one heat exchanger at a hydraulic fluid flow rate of 3 gpm. As further shown inFIG. 8, at a hydraulic fluid flow rate of 4 gpm, the heat dissipation of the hydraulic fluid flow passing through one heat exchanger is slightly less than 600 BTU/min, and the hydraulic fluid flow passing through two heat exchangers is slightly less than 800 BTU/min. Thus, a greater benefit is shown with having two heat exchangers over one heat exchanger at a hydraulic fluid flow rate of 4 gpm. As further shown inFIG. 8, at a hydraulic fluid flow rate of 5 gpm, the heat dissipation of the hydraulic fluid flow passing through one heat exchanger is about 600 BTU/min, and the hydraulic fluid flow passing through two heat exchangers is about 900 BTU/min. Thus, an even greater benefit is shown with having two heat exchangers over one heat exchanger at a hydraulic fluid flow rate of 5 gpm. As further shown inFIG. 8, at a hydraulic fluid flow rate of 6 gpm to 10 gpm, the hydraulic fluid flow passing through one heat exchanger starts to decrease from about slightly less than 600 BTU/min to slightly more than 100 BTU/min, while the hydraulic fluid flow passing through two heat exchangers continues to increase from 1000 BTU/min to 1200 BTU/min. Preferably, when there are at least two heat exchangers positioned in parallel to each other and used with two pump devices34(seeFIG. 4), such as a primary pump device36and a demand pump device38, the hydraulic fluid flow rate is 5 gpm to 8 gpm, which was found to exhibit a surprisingly beneficial total heat dissipation and hydraulic fluid flow for use in embodiments of the hydraulic fluid heat dissipation control assembly28of an aircraft hydraulic system26.

FIG. 9is an illustration of a total heat dissipation from heat exchangers graph96showing heat dissipation in BTU/min (British thermal units per minute) versus percent (%) (hydraulic fluid) flow passing one heat exchanger where there are two heat exchangers positioned in parallel to each other.FIG. 9shows a percent (hydraulic fluid) flow passing through one heat exchanger-heat dissipation measurements plot line98. The measurements for the one heat exchanger-heat dissipation measurements plot line98were taken at a hydraulic fluid flow temperature of 220° F. (degrees Fahrenheit), a fuel temperature of 120° F. (degrees Fahrenheit), and a total fluid flow rate of 8.5 gpm. As shown inFIG. 9, if the percent hydraulic fluid flow passing one heat exchanger is 10% (the other heat exchanger would have a percent hydraulic fluid flow of 90%) or 90% (the other heat exchanger would have a percent hydraulic fluid flow of 10%), the heat dissipation is about 650 BTU/min for both. As further shown inFIG. 9, if the percent hydraulic fluid flow passing one heat exchanger is 50% (the other heat exchanger would have a percent hydraulic fluid flow of 50%), the heat dissipation is about 1200 BTU/min, which may be advantageously efficient. In addition, as further shown inFIG. 9, if the percent hydraulic fluid flow passing one heat exchanger is 40% (the other heat exchanger would have a percent hydraulic fluid flow of 60%), or 60% (the other heat exchanger would have a percent hydraulic fluid flow of 40%), the heat dissipation is about 1150 BTU/min, which may also be advantageously efficient. Preferably, when there are at least two identical heat exchangers positioned in parallel to each other and used with two pump devices34(seeFIG. 4), such as a primary pump device36and a demand pump device38, the percent hydraulic fluid flow passing one heat exchanger is between about 40% to about 60%, which was found to exhibit a surprisingly beneficial total heat dissipation and efficiency for use in embodiments of the hydraulic fluid heat dissipation control assembly28of an aircraft hydraulic system26. The heat dissipation may be calculated with the following formula: Heat Dissipation=(cpρ)×(Q)×(Tinminus Tout), where cpis specific heat, ρ is hydraulic fluid density, Q is hydraulic fluid flow rate, Tinis the hydraulic fluid temperature at the heat exchanger inlet or entrance, and Toutis the hydraulic fluid temperature at the heat exchanger outlet or exit.

Thus, the pressure differential across the heat exchanger40may be used through a pressure control valve46to control the hydraulic fluid flow through the heat exchangers40, so as to vary the heat dissipation from the aircraft hydraulic system26. With respect to the hydraulic fluid heat dissipation control assembly28aofFIG. 2, the pressure differential across the heat exchanger40varies with the hydraulic fluid temperature due to hydraulic fluid viscosity changes with the temperature, in order to achieve controlled heat dissipation based on the fluid temperature. As discussed above with respect to the hydraulic fluid heat dissipation control assemblies28b,28cofFIGS. 4 and 5, respectively, the pressure differential also changes with the hydraulic fluid flow passing through the heat exchanger but due to the resistance associated with the hydraulic fluid flow, in order to control the heat dissipation based on pump running conditions.

In another embodiment of the disclosure, there is provided an aircraft10(seeFIG. 1) having an aircraft hydraulic system26(seeFIG. 1) with a hydraulic fluid heat dissipation control assembly28(seeFIG. 1). The aircraft10comprises a fuselage12, a pair of wings18operatively coupled to the fuselage12, and an aircraft hydraulic system26disposed within at least one of the fuselage12and the wings18. The aircraft hydraulic system26comprises a hydraulic fluid heat dissipation control assembly28(seeFIG. 1). The hydraulic fluid heat dissipation control assembly28comprises at least one fluid flow line30, such as in the form of case drain flow line31(seeFIGS. 2, 4, 5). The hydraulic fluid heat dissipation control assembly28further comprises one or more pump devices34(seeFIGS. 2, 4, 5) coupled to the at least one fluid flow line30, such as in the form of case drain flow line31. The hydraulic fluid heat dissipation control assembly28further comprises one or more heat exchangers40(seeFIGS. 2, 4, 5) coupled to the at least one fluid flow line30, such as in the form of case drain flow line31(seeFIGS. 2, 4, 5). The hydraulic fluid heat dissipation control assembly28further comprises at least one pressure control valve46(seeFIGS. 2, 4, 5) coupled to the at least one fluid flow line30, such as in the form of case drain flow line31. The pressure control valve46controls flow and heat dissipation of the hydraulic fluid32(seeFIGS. 2, 4, 5) from the one or more pump devices34through the at least one fluid flow line30, such as in the form of case drain flow line31, and through the one or more heat exchangers40in order to obtain a heat dissipation controlled hydraulic fluid50(seeFIGS. 2, 4, 5). The heat dissipation controlled hydraulic fluid50then flows to the return flow line52(seeFIGS. 2, 4, 5) or to the hydraulic fluid reservoir54(seeFIGS. 2, 4, 5) which are both located in the aircraft hydraulic system26. Specific embodiments of the hydraulic fluid heat dissipation control assembly28that may be installed in the aircraft hydraulic system26of the aircraft10(seeFIG. 1) are discussed in detail above.

In another embodiment of the disclosure, as shown inFIG. 10, there is provided a method200of controlling heat dissipation of a hydraulic fluid32(seeFIGS. 2, 4, 5) in an aircraft hydraulic system26(seeFIGS. 2, 4, 5).FIG. 10is a flow diagram illustrating an exemplary method200of the disclosure.

As shown inFIG. 10, the method200comprises step202of installing a hydraulic fluid heat dissipation control assembly28(seeFIGS. 2, 4, 5) in an aircraft hydraulic system26(seeFIG. 1). The method200controls heat dissipation of a hydraulic fluid32(seeFIGS. 2, 4, 5) in the aircraft hydraulic system26to condition the hydraulic fluid32to maintain an optimum hydraulic fluid temperature, such that the hydraulic fluid32is not overheated for hot day operations or conditions and such that the hydraulic fluid32retains heat to ensure adequate hydraulic performance for cold day operations or conditions.

The hydraulic fluid heat dissipation control assembly28used in the method200comprises at least one fluid flow line30(seeFIGS. 2, 4, 5) positioned in the aircraft hydraulic system26. The at least one fluid flow line30preferably comprises a case drain flow line31(seeFIGS. 2, 4, 5). The hydraulic fluid heat dissipation control assembly28further comprises one or more pump devices34(seeFIGS. 2, 4, 5) coupled to the at least one fluid flow line30. The one or more pump devices34may comprise, for example, one or more primary pump devices36(seeFIGS. 4, 5), one or more demand pump devices38(seeFIGS. 4, 5), or another suitable pump device34.FIG. 2shows one pump device34which may comprise either one primary pump device36or one demand pump device38.FIGS. 4 and 5show two pump devices34comprising one primary pump device36and one demand pump device38.

The hydraulic fluid heat dissipation control assembly28further comprises one or more heat exchangers40coupled to the at least one fluid flow line30. The one or more heat exchangers40are preferably located in one or more fuel tanks42, for example, either together in one fuel tank42or separately in two or more fuel tanks42. In one embodiment, as shown inFIG. 2, the hydraulic fluid heat dissipation control assembly28may have two heat exchangers40positioned in parallel to each other in one fuel tank42. In another embodiment, as shown inFIG. 5, the hydraulic fluid heat dissipation control assembly28may have two heat exchangers40a,40b, with one heat exchanger40alocated in one fuel tank42a, and with the other heat exchanger40blocated in another fuel tank42b. In another embodiment, as shown inFIG. 4, the hydraulic fluid heat dissipation control assembly28may have three heat exchangers40a,40b,40c, with heat exchangers40a,40bpositioned in parallel to each other in fuel tank42a, and heat exchanger40clocated in fuel tank42b.

The hydraulic fluid heat dissipation control assembly28further comprises at least one flow control element44(seeFIGS. 2, 4, 5) coupled to the at least one fluid flow line30. Preferably, the at least one flow control element44comprises a pressure control valve46(seeFIGS. 2, 4, 5).FIGS. 2, 4, and 5each show one flow control element44in the form of pressure control valve46. However, additional flow control elements44may also be used.

As shown inFIGS. 2, 4 and 5, the hydraulic fluid heat dissipation control assembly28may further comprise a pressure line56coupled to the return flow line52via the one or more pump devices34. The hydraulic fluid heat dissipation control assembly28may further comprise one or more filters58(seeFIGS. 2, 4, 5). Specific embodiments of the hydraulic fluid heat dissipation control assembly28that may be used in the method200are discussed in detail above.

The method200further comprises step204of sensing with the at least one flow control element44a pressure differential across one or at least one of the one or more heat exchangers40. In one embodiment, as shown inFIG. 2, for the sensing step204of the method200, the pressure differential varies with a temperature of the hydraulic fluid32. In other embodiments, as shown inFIGS. 4, 5, for the sensing step204, the one or more pump devices34comprise one or more demand pump devices36, and the pressure differential varies with a pump running condition of the one or more demand pump devices36. In one embodiment of the method200, as shown inFIG. 5, the one or more pump devices34comprise one or more primary pump devices36, and the hydraulic fluid heat dissipation control assembly28has one flow control element44positioned in a by-pass path60(seeFIG. 5), so that a pump running condition of each of the one or more primary pump devices36has none of the one or more heat exchangers40in operation.

The method200further comprises step206of controlling with the at least one flow control element44the flow of the hydraulic fluid32through the two or more heat exchangers40so as to vary heat dissipation from the aircraft hydraulic system26and so as to obtain a heat dissipation controlled hydraulic fluid50(seeFIGS. 2, 4, 5). The method200further comprises step208of flowing the heat dissipation controlled hydraulic fluid50to one of at least the return flow line52(seeFIGS. 2, 4, 5) or to the hydraulic fluid reservoir54(seeFIGS. 2, 4, 5) which are both located in the aircraft hydraulic system26.

Embodiments of the hydraulic fluid heat dissipation control assembly28(seeFIGS. 2, 4, 5) and method200(seeFIG. 10) for an aircraft hydraulic system26allow for controlled heat dissipation through a pressure differential which varies with fluid temperature or pump running conditions and is convenient to be sensed. In addition, embodiments of the hydraulic fluid heat dissipation control assembly28(seeFIGS. 2, 4, 5) and method200(seeFIG. 10) provide a way to control the heat dissipation so the operational limitations or restrictions associated with known solutions of “no heat exchanger” or “heat exchanger with fixed effect” may be eliminated. Further, embodiments of the hydraulic fluid heat dissipation control assembly28(seeFIGS. 2, 4, 5) and method200(seeFIG. 10) for an aircraft hydraulic system26control the heat dissipation from an aircraft hydraulic system26, so the hydraulic fluid32preferably will not be overheated for hot day operations or conditions, and the hydraulic fluid32in the aircraft hydraulic system26preferably will retain heat to ensure adequate hydraulic performance for cold day operations or conditions. This may result in less operation restrictions as hydraulic fluid temperature related restrictions for cold day and hot day operations or conditions may be eliminated. This may further result in performance improvement as warmer hydraulic fluid temperature may result in better hydraulic performance for cold day operations or conditions.

In addition, embodiments of the hydraulic fluid heat dissipation control assembly28(seeFIGS. 2, 4, 5) and method200(seeFIG. 10) for an aircraft hydraulic system26provide for controlling hydraulic heat dissipation, for flowing the hydraulic fluid32to at least one fluid flow line30(seeFIGS. 2, 4, 5), such as in the form of a case drain flow line31(seeFIGS. 2, 4, 5) from one or more pump devices34(seeFIGS. 2, 4, 5) to condition the hydraulic fluid32in the aircraft hydraulic system26and more effectively maintain an optimum hydraulic fluid temperature.

Finally, embodiments of the hydraulic fluid heat dissipation control assembly28(seeFIGS. 2, 4, 5) and method200(seeFIG. 10) for an aircraft hydraulic system26may provide such benefits as removing various restrictions on operating aircraft in high temperatures, lowering system weight by optimization of the design, such as by sizing aircraft hydraulic systems at an elevated fluid temperature to reduce hydraulic tubing sizes, and reducing costs such as by eliminating expensive and long lead times to develop a thermostat control valve. Moreover, the hydraulic fluid heat dissipation control assembly28and method200may further reduce costs by utilizing existing, low cost components, e.g., heat exchangers, pressure control valve, and hydraulic tubing for the fluid flow lines. Finally, the performance of the hydraulic fluid heat dissipation control assembly28may be more reliable than known assemblies and systems and preferably requires no maintenance in service as compared to known thermostat control systems.

Many modifications and other embodiments of the disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. The embodiments described herein are meant to be illustrative and are not intended to be limiting or exhaustive. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.