Abstract:
A thermal management system is provided. The thermal management system includes a first hydraulic system for circulating a first hydraulic fluid at a first temperature, a second hydraulic system for circulating a second hydraulic fluid at a second temperature that is higher than the first temperature, and a heat exchanger coupling the first hydraulic system to the second hydraulic system, wherein the heat exchanger is configured to exchange heat between the first hydraulic fluid and the second hydraulic fluid.

Description:
BACKGROUND 
     The present disclosure relates generally to thermal management, and more particularly to systems and methods for use in balancing and transporting heat among hydraulic systems within an aircraft. 
     In at least some known aircraft, heat from one or more hydraulic systems is dissipated into fuel through a heat exchanger located inside a fuel tank. Other known aircraft have no hydraulic system heat exchangers and address hydraulic fluid heating through restrictions and limitations on operation of such aircraft when an outside ambient temperature is above a predetermined threshold. Additionally, some known aircraft include a thermostat control to selectively cause hydraulic fluid to bypass a heat exchanger, in order to retain heat and to reduce pressure loss in hydraulic lines when the outside ambient temperature is below a predetermined threshold. Additionally, some known aircraft use hydraulic system circulating flow to control the temperature of hydraulic fluid. More specifically, in such aircraft, hydraulic orifice valves are installed in extremities of hydraulic systems to adjust system internal leakage so as to control heat generated through the orifices and total heat loss from hydraulic tubing to the ambient. Additionally, some known aircraft use guided ram air flow to cool the temperature of hydraulic fluid. Accordingly, such systems require substantial modification to structural surfaces of an aircraft. In summary, there exists a need for a cost-effective and efficient system for heating and cooling of hydraulic fluid within an aircraft. 
     BRIEF DESCRIPTION 
     In one aspect, a thermal management system is provided. The thermal management system includes a first hydraulic system for circulating a first hydraulic fluid at a first temperature, a second hydraulic system for circulating a second hydraulic fluid at a second temperature that is higher than the first temperature, and a heat exchanger coupling the first hydraulic system to the second hydraulic system, wherein the heat exchanger is configured to exchange heat between the first hydraulic fluid and the second hydraulic fluid. 
     In another aspect, an aircraft is provided. The aircraft includes a first hydraulic system for circulating a first hydraulic fluid at a first temperature, a second hydraulic system for circulating a second hydraulic fluid at a second temperature that is higher than the first temperature, and a heat exchanger coupling the first hydraulic system to the second hydraulic system. The heat exchanger is configured to exchange heat between the first hydraulic fluid and the second hydraulic fluid. 
     In another aspect, a method for managing temperatures in a machine is provided. The method includes circulating a first hydraulic fluid at a first temperature through a first hydraulic system coupled to the machine. The method additionally includes circulating a second hydraulic fluid at a second temperature that is different from the first temperature through a second hydraulic system coupled to the machine. The method also includes exchanging heat between the first hydraulic fluid and the second hydraulic fluid with a heat exchanger that couples the first hydraulic system to the second hydraulic system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an example aircraft that includes hydraulic systems and aircraft operating components that are powered by the hydraulic systems. 
         FIG. 2  is a block diagram of a first example configuration of the hydraulic systems of the aircraft of  FIG. 1 . 
         FIG. 3  is a block diagram of a second example configuration of the hydraulic systems of the aircraft of  FIG. 1 . 
         FIG. 4  is a graph of temperatures of the hydraulic systems of  FIG. 1  when the hydraulic systems are not coupled by a heat exchanger. 
         FIG. 5  is a graph of temperatures of the hydraulic systems of  FIG. 1  when the hydraulic systems are coupled by a heat exchanger. 
         FIG. 6  is another graph of temperatures of the hydraulic systems of  FIG. 1  when the hydraulic systems are not coupled by a heat exchanger. 
         FIG. 7  is another graph of temperatures of the hydraulic systems of  FIG. 1  when the hydraulic systems are coupled by a heat exchanger. 
         FIG. 8  is a flowchart of a method for managing temperatures in a machine, such as the aircraft of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagram of an aircraft  100  that includes a first hydraulic system  102  and a second hydraulic system  104 . First hydraulic system  102  and second hydraulic system  104  are coupled together by a heat exchanger  106 . First hydraulic system  102  is pressurized by a pump device  204  that is driven by an engine  108  of aircraft  100  and provides power for certain operating components of aircraft  100 . For example, first hydraulic system  102  powers at least one spoiler  110 , at least one aileron  111 , at least one elevator  112 , and/or at least one rudder  114  in aircraft  100 . Additionally, second hydraulic system  104  powers components of aircraft  100  similar to the first hydraulic system and, in addition, other components that are not powered by first hydraulic system  102 . For example, second hydraulic system  104  powers landing gear  116  and/or brakes  118  of aircraft  100 . In some implementations, first hydraulic system  102  is routed in a way that more heat is dissipated from hydraulic tubing to surrounding ambient and causes hydraulic fluid within first hydraulic system  102  to be colder than hydraulic fluid in second hydraulic system  104 . In some implementations, second hydraulic system  104  uses a pump  214  that may be different from pump  204  used in first hydraulic system  102  and may generate more heat than pump  204 , resulting in a warmer second hydraulic system  104 . In some implementations, aircraft  100  may include additional hydraulic systems that power other components of aircraft  100 . Additionally, in some implementations, aircraft  100  is any other machine that includes at least two hydraulic systems coupled by heat exchanger  106 . 
       FIG. 2  is a block diagram of a first example configuration of first hydraulic system  102  and second hydraulic system  104 . Heat exchanger  106  couples first hydraulic system  102  with second hydraulic system  104  such that heat is exchanged from second hydraulic system  104  to first hydraulic system  102 . Heat exchanger  106  includes a first tube  120  and a second tube  122 . First tube  120  is coupled in flow communication with first hydraulic system  102  and second tube  122  is coupled in flow communication with second hydraulic system  104 . First tube  120  surrounds second tube  122 , thereby enabling heat to be exchanged between first hydraulic system  102  and second hydraulic system  104  without mixing first hydraulic fluid  201  with second hydraulic fluid  211 . 
     In first hydraulic system  102 , a first hydraulic fluid  201  flows through a return line  200 , which may be a trunk return line, through first tube  120  of heat exchanger  106 , and then to a reservoir  202 . A pump  204  is located downstream of reservoir  202  and pumps first hydraulic fluid  201  through a pressure line  208 . A case drain  206  is coupled to pump  204  and to reservoir  202  and routes any of first hydraulic fluid  201  that leaks out of pump  204  back to reservoir  202 . In second hydraulic system  104 , a second hydraulic fluid  211  flows through a return line  210  to a reservoir  212  and then to a pump  214 . Pump  214  pumps second hydraulic fluid  211  through a pressure line  218 . Additionally, a case drain  216  is coupled to pump  214  and to reservoir  212 . Case drain  216  routes any of second hydraulic fluid  211  that leaks out of pump  214  through second tube  122  of heat exchanger  106  and back to reservoir  212 . As a characteristic of a hydraulic pump, for example pump  204 , case drain fluid carries heat due to pump inefficiency and is, for example, 30 degrees Fahrenheit hotter than the pump inlet fluid from a reservoir, for example reservoir  202 . Therefore, fluid in case drain  206  of pump  204  may be, for example, 30 degrees Fahrenheit hotter than fluid in reservoir  202  and fluid in case drain  216  of pump  214  may be, for example, approximately 30 degrees Fahrenheit hotter than fluid in reservoir  212 . Additionally, second hydraulic system  104  may be, for example, 20 degrees Fahrenheit hotter than first hydraulic system  102 , as described above. As a result, second hydraulic fluid  211  flowing through second tube  122  of heat exchanger  106  may be maintained at a higher temperature (for example, approximately 50 degrees Fahrenheit, assuming no heat is exchanged) than first hydraulic fluid  201  flowing through first tube  120  of heat exchanger  106 . 
       FIG. 3  is a block diagram of a second example configuration of first hydraulic system  102  and second hydraulic system  104  of aircraft  100 . More specifically, heat exchanger  106  couples first hydraulic system  102  with second hydraulic system  104  in a different location than in  FIG. 2 . In first hydraulic system  102 , first hydraulic fluid  201  flowing through pressure line  208  is received in a first actuator  300 , which may control, for example, spoiler  110  (shown in  FIG. 1 ) and a second actuator  302 , which may control, for example, elevator  112  (shown in  FIG. 1 ). First hydraulic fluid  201  then passes through return line  200 , which may be a branch return line, and through first tube  120  of heat exchanger  106 . Second hydraulic system  104  is configured as described with reference to  FIG. 2 . The configuration shown in  FIG. 3  may be used instead of or in addition to the configuration shown in  FIG. 2  depending on design considerations, for example available space for components and/or how close first hydraulic system  102  is to second hydraulic system  104  at various points in aircraft  100 . 
       FIG. 4  is a graph of temperatures of first hydraulic system  102  and second hydraulic system  104  when first hydraulic system  102  and second hydraulic system  104  are not coupled together by heat exchanger  106 . The outside ambient temperature is a first ambient temperature. The temperature of first hydraulic fluid  201  in case drain  206  is represented by curve  400  and the temperature of second hydraulic fluid  211  in case drain  216  is represented by curve  402 . As time progresses, the temperature in case drain  216  exceeds the temperature in case drain  206 . After a first time period elapses, the temperature in case drain  216  is a first number of degrees Fahrenheit higher than the temperature in case drain  206 . 
       FIG. 5  is a graph of temperatures of first hydraulic system  102  and second hydraulic system  104  when first hydraulic system  102  and second hydraulic system  104  are coupled together by heat exchanger  106 . The outside ambient temperature is, again, the first ambient temperature. The temperature of first hydraulic fluid  201  in case drain  206  is represented by curve  500  and the temperature of second hydraulic fluid  211  in case drain  216  is represented by curve  502 . As compared to curves  400  and  402  of  FIG. 4 , curves  500  and  502  indicate that, after the first time period has elapsed, the temperatures in case drains  206  and  216  differ by a second number of degrees that is less than the first number of degrees. More specifically, heat exchanger  106  facilitates cooling second hydraulic fluid  211  in second hydraulic system  104  by transferring heat to first hydraulic fluid  201  in first hydraulic system  102 . 
       FIG. 6  is another graph of temperatures of first hydraulic system  102  and second hydraulic system  104  when first hydraulic system  102  and second hydraulic system  104  are not coupled together by heat exchanger  106 . The outside ambient temperature is a second ambient temperature that is less than the first ambient temperature. The temperature of second hydraulic fluid  211  in case drain  216  is represented by curve  600  and the temperature of first hydraulic fluid  201  in case drain  206  is represented by curve  602 . As time progresses, the temperature in case drain  216  exceeds the temperature in case drain  206 . After the first time period has elapse, the temperature in case drain  216  is a third number of degrees Fahrenheit higher than the temperature in case drain  206 . The temperature of case drain  206  is stabilized and the temperature of reservoir  202  is lower than the temperature of case drain  206 . The temperature of reservoir  202  is considered representative of a hydraulic system temperature that may not provide a preferred amount of hydraulic power for takeoff. 
       FIG. 7  is another graph of temperatures of first hydraulic system  102  and second hydraulic system  104  when first hydraulic system  102  and second hydraulic system  104  are coupled together by heat exchanger  106 . The outside ambient temperature is, again, the second ambient temperature. The temperature of second hydraulic fluid  211  in case drain  216  is represented by curve  700  and the temperature of first hydraulic fluid  201  in case drain  206  is represented by curve  702 . As compared to curves  600  and  602  of  FIG. 6 , curves  700  and  702  indicate that the temperatures in case drains  206  and  216  differ by a fourth number of degrees Fahrenheit after the first time period has elapsed. The fourth number of degrees is less than the third number of degrees discussed with reference to  FIG. 6 . More specifically, heat exchanger  106  facilitates heating first hydraulic fluid  201  in first hydraulic system  102  with heat transferred from second hydraulic fluid  211  in second hydraulic system  104 . 
       FIG. 8  is a flowchart of a method  800  for managing temperatures in a machine, such as aircraft  100  (shown in  FIG. 1 ). Method  800  includes circulating  802  a first hydraulic fluid, for example first hydraulic fluid  201 , at a first temperature through a first hydraulic system, for example first hydraulic system  102 . First hydraulic system  102  is coupled to a machine, for example aircraft  100 . Additionally, method  800  includes circulating  804  a second hydraulic fluid, for example second hydraulic fluid  211 , at a second temperature that is different from the first temperature through a second hydraulic system, for example second hydraulic system  104 . Second hydraulic system  104  is coupled to the machine, for example aircraft  100 . Method  800  additionally includes exchanging  806  heat between the first hydraulic fluid  201  and the second hydraulic fluid  211  with a heat exchanger that couples first hydraulic system  102  to second hydraulic system  104 . The heat exchanger may be, for example, heat exchanger  106 . 
     As compared to known methods and systems for heating or cooling hydraulic fluid within an aircraft, the methods and systems described herein facilitate both heating and cooling hydraulic fluid with the same setup, and in a more efficient and cost-effective way by coupling hydraulic systems of different temperatures together with a heat exchanger. 
     The description of the different advantageous implementations has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the implementations in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous implementations may provide different advantages as compared to other advantageous implementations. The implementation or implementations selected are chosen and described in order to best explain the principles of the implementations, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various implementations with various modifications as are suited to the particular use contemplated. This written description uses examples to disclose various implementations, which include the best mode, to enable any person skilled in the art to practice those implementations, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.