Abstract:
A method is disclosed for making an air temperature sensor comprises first generating a digital model of an air temperature sensor housing. The digital model is inputted into an additive manufacturing apparatus comprising an energy source. The additive manufacturing apparatus applies energy from the energy source to successively applied incremental quantities of a fusible material. The energy source fuses the successively applied incremental quantities of the fusible material to form incremental portions of the air temperature sensor housing that accrete together to form the air temperature sensor housing

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to an air temperature sensor, and specifically to methods of manufacturing a housing for such a sensor. 
         [0002]    Air temperature sensors are used in a wide variety of industrial and vehicular applications. Total air temperature probes are often used on aircraft or other vehicles for measuring outside air temperature. Modem jet powered aircraft require very accurate measurement of outside air temperature (OAT) for inputs to the air data computer, engine thrust management computer, and other airborne systems. For these aircraft types, their associated flight conditions, and the use of total air temperature probes in general, air temperature is better defined by the following four temperatures: (1) Static air temperature (SAT) or (TS), (2) total air temperature (TAT) or (Tt), (3) recovery temperature (Tr), and (4) measured temperature (Tm). Static air temperature (SAT) or (TS) is the temperature of the undisturbed air through which the aircraft is about to fly. Total air temperature (TAT) or (Tt) is the maximum air temperature that can be attained by 100% conversion of the kinetic energy of the flight. The measurement of TAT is derived from the recovery temperature (Tr), which is the adiabatic value of local air temperature on each portion of the aircraft surface due to incomplete recovery of the kinetic energy. Temperature (Tr) is in turn obtained from the measured temperature (Tm), which is the actual temperature as measured, and which differs from recovery temperature because of heat transfer effects due to imposed environments. For measuring the TAT, TAT probes are well known in the art. These probes can be of a wide range of different types and designs, and can be mounted on various aircraft surfaces which expose the TAT probe to airflow. For example, common TAT probe mounting locations include aircraft engines and aircraft fuselages. 
         [0003]    Of critical importance for temperature sensors such as total air temperature sensors is providing a housing that protects the temperature sensing element while delivering a continuous regulated flow of outside air to the temperature sensing element that accurately represents the temperature of the outside air (i.e., avoiding recirculating eddy currents that could lead to a false temperature measurement). It is also important to avoid ice buildup that could interfere with accurate temperature measurement, which is often accomplished by providing a heat source proximate to the sensor. In such cases, it is important to shield the sensing element from the heat source so that heat from the heat source does not interfere with accurate temperature measurement. In order to meet these objectives, air temperature sensor housing often has multiple chambers or passages to control airflow and provide radiation shielding, along with supports, braze, weld, or adhesive joints, and other features to provide structural integrity. The resulting structure is relatively complex, often consisting of dozens of parts with dozens of weld/braze joints. Such complexity in a relatively small structure often leads to variations in assembly, which can lead to variations in quality and performance, as well as higher manufacturing costs. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to some aspects of the invention, a method for making an air temperature sensor comprises first generating a digital model of an air temperature sensor housing. The digital model is inputted into an additive manufacturing apparatus comprising an energy source. The additive manufacturing apparatus applies energy from the energy source to successively applied incremental quantities of a fusible material. The energy source fuses the successively applied incremental quantities of the fusible material to form incremental portions of the air temperature sensor housing that accrete together to form the air temperature sensor housing. 
         [0005]    In some aspects of the invention, the air temperature sensor housing includes an air inlet, a first conduit in fluid communication with the air inlet, an air outlet in fluid communication with the channel, and a sensor support structure configured to retain a temperature sensor element mounted in the channel. 
         [0006]    In some aspects of the invention, the air temperature sensor housing includes at least one special feature fabricated by the repeated application of energy to successively applied incremental quantities of fusible material. One such special feature is the sensor support structure, integral with the housing. Another special feature is a non-circular opening as an outlet in one of the airflow conduits. Another feature is an air swirler integral with and extending inwardly from a conduit. Yet another feature is an ice barrier integral with and extending inwardly from a conduit. The repeated application of energy to successively applied incremental quantities of fusible material can also be used to fabricate varied surface texture on an inner surface of a conduit to impact airflow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1A  is a schematic depiction of an air temperature sensor housing cross-section; 
           [0009]      FIG. 1B  is a schematic depiction of the air temperature sensor housing cross-section of  FIG. 1A  with a temperature sensing element therein; 
           [0010]      FIG. 2  is a zoom view of a portion of the housing of  FIG. 1A ; and 
           [0011]      FIG. 3  is a view of a housing with an integrated structure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Referring now to the Figures,  FIGS. 1A and 1B  schematically depict an air temperature sensor  10 . As shown in  FIGS. 1A and 1B , an air temperature sensor includes an air temperature sensor housing  10  with a first conduit or tube  12  having an inlet  14 . In some embodiments, the inlet can have a scoop (not shown), which can include a 90° or more bend if, for example, the housing is mounted with the longitudinal axis of the first tube  12  transverse to the direction of outside airflow. As is known in the art, one or more airfoils (not shown) can also be associated with the inlet  14 . First tube  12  has a first section  12 ′ having a first radial opening cross-section and a second section  12 ″ having a second radial opening cross-sectional area smaller than the first radial opening cross-section. Also depicted is a transition between sections  12 ′ and  12 ″ with a ramped wall connecting the tube wall of section  12 ′ and section  12 ″ having a radial opening cross-section of intermediate cross-sectional area between the cross-sectional area of sections  12 ′ and  12 ″. The first tube  12  includes mounting sockets  16  and can include supports  18  and  20  for securing and supporting temperature sensing elements  22  and  24  within the first tube  12 . It should be noted here that  FIGS. 1A and 1B  are identical except for the presence of the temperature sensing elements  22 ,  24 , which are omitted from  FIG. 1A  for ease of illustration. As shown in more detail in  FIG. 2 , in some embodiments the supports configured like support  18 , having a wall engagement section  18 ′ protruding radially inwardly from the wall of the first tube  12 , and a sensing element engagement section  18 ″. In some embodiments, as shown in  FIGS. 1 and 2 , the wall engagement section  18 ′ has an axially-extending surface portion  18 ′″ that is angled with respect to the tube wall. The angled structures ( 20 ,  18 ,  34 ) can be built without the use of 3D build support structures that would then require post process removal. Incorporating the self-support angles speeds build time and reduces post build processing time. The angle with respect to the longitudinal direction of the tube wall can be greater than 0° and less than 90°, and more specifically can range from 0° to 60°. First tube  12  also has outlet openings  26 . In operation, outside air enters the first tube  12  through opening  14 , flows past and around the temperature sensing elements  22 ,  24  where temperature is measured, and exits through outlet openings  26 . 
         [0013]    In some embodiments, a second conduit or tube  28  is disposed concentrically around the first tube  12 . The second tube  28  can protect the first tube from damage and radiation (e.g., heat radiation), as well as contribute to airflow management. For example, in many applications, such as on aircraft, the temperature sensor can be mounted on the fuselage or a forward-facing portion of an engine nacelle where they can be subject to ice formation, which can adversely affect the accuracy of temperature measurements. Therefore auxiliary heat is often provided in proximity to the exterior of the temperature sensor housing. The second tube  28  can provide radiation (heat) shielding around the first tube to limit the impact of external heat sources on the accuracy of the temperature measurement. In some embodiments, for airflow management purposes, a portion of air captured by an external air scoop (not shown) can be directed into the annular space  30  between the first tube  12  and the second tube  28  instead of the space inside first tube  12 . In some embodiments, support tabs  34  are disposed between the first tube  12  and second tube  28  to maintain the radial position of the first tube within the second tube and to provide structural integrity. Support tabs  34  can be mechanically attached to both tubes  12  and  28 , or can be attached to only one of the tubes  12  or  28  with an interference fit between itself and the other tube. Second tube  28  also includes outlet openings  32  for air exiting the sensor housing  10 . The openings can be any shape. In some embodiments, either or both of the openings  26 ,  32  are non-circular, such as trapezoidal shaped. The non-circular openings of  26  and  32  incorporate self-supporting angles that allow for the passages to be built without 3D printed support material, which can increase build speed while reducing post build processing time. 
         [0014]    Additive manufacturing techniques can also be used to provide other features not readily feasible for inner conduit walls. Examples of such features can include ice barrier to either prevent ice formation or to direct any ice that does form to form in areas where it is not problematic. Other such features can include air swirlers or deflectors to create desired airflow patterns.  FIG. 3  depicts the sensor housing from  FIG. 1  with an ice barrier or air swirler  34  disposed on the inner wall of first tube  12 . In some embodiments, multiple swirlers or ice dams can be disposed spaced circumferentially or axially on the tube wall, for example a plurality of swirlers could be disposed on a tube wall circumferentially evenly spaced around a position on the axis of the tube to provide a symmetric pattern of airflow displacement such as a vortex. 
         [0015]    The digital models used in the practice of the invention are well-known in the art, and do not require further detailed description here. The digital model can be generated from various types of computer aided design (CAD) software, and various formats are known, including but not limited to SLT (standard tessellation language) files, AMF (additive manufacturing format) files, PLY files, wavefront (.obj) files, and others that can be open source or proprietary file formats. 
         [0016]    Various types of additive manufacturing materials, energy sources, and processes can be used to fabricate the air temperature sensor housing and the individual features thereof that are described herein. The type of additive manufacturing process used depends in part on the type of material out of which it is desired to manufacture the sensor housing. In some embodiments, the sensor housing is made of metal, and a metal-forming additive manufacturing process can be used. Such processes can include selective laser sintering (SLS) or direct metal laser sintering (DMLS), in which a layer of metal or metal alloy powder is applied to the workpiece being fabricated and selectively sintered according to the digital model with heat energy from a directed laser beam. Another type of metal-forming process includes selective laser melting (SLM) or electron beam melting (EBM), in which heat energy provided by a directed laser or electron beam is used to selectively melt (instead of sinter) the metal powder so that it fuses as it cools and solidifies. Various metals and metal alloys can be used, including but not limited to CoCr, stainless steels, nickel base alloys, aluminum and titanium alloys. In some embodiments, the sensor housing is made of a polymer, and a polymer or plastic forming additive manufacturing process can be used. Such process can include stereolithography (SLA), in which fabrication occurs with the workpiece disposed in a liquid photopolymerizable composition, with a surface of the workpiece slightly below the surface. Light from a laser or other light beam is used to selectively photopolymerize a layer onto the workpiece, following which it is lowered further into the liquid composition by an amount corresponding to a layer thickness and the next layer is formed. Polymer housings can also be fabricated using selective heat sintering (SHS), which works analogously for thermoplastic powders to SLS for metal powders. Another exemplary additive manufacturing process that can be used for polymers or metals is fused deposition modeling (FDM), in which a metal or thermoplastic feed material (e.g., in the form of a wire or filament) is heated and selectively dispensed onto the workpiece through an extrusion nozzle. 
         [0017]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.