Abstract:
An aircraft environmental conditioning system is disclosed having an air cycle machine for conditioning an airflow comprising hot compressed air by reducing its temperature and pressure. The air cycle machine is disposed in a housing in an unpressurized area of the aircraft, and produces conditioned pressurized air for delivery to a pressurized area of the aircraft. The system also includes a vibration sensor disposed within the housing, and a controller in communication with the vibration sensor that is configured to respond to vibration detected by the vibration sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority to U.S. Provisional Patent Application Ser. No. 61/988,031, filed May 2, 2014, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to environmental air conditioning systems (ECS), and more specifically to air cycle environmental air conditioning systems such as used on aircraft. 
         [0003]    Aircraft that fly at altitudes above that at which ambient air is suitable for crew, passengers, cargo, or equipment are often equipped with air cycle environmental air conditioning systems to provide pressurized conditioned air. These air conditioning systems typically utilize a pressurized air bleed from a turbine fan engine or an auxiliary power unit (APU), or in some cases from an electrically-powered compressor as a source of compressed air that flows along an airflow path through the air cycle environmental air conditioning system to produce conditioned air for the cockpit and passenger cabin or other pressurized areas of the aircraft. The compressed air that is fed into these systems is typically at a temperature and pressure far in excess of the normal temperature and pressure for conditioned air to be supplied to the cockpit and passenger cabin, so it must be expanded and cooled by the air conditioning system before it can be discharged as conditioned air. Aviation air cycle environmental conditioning systems typically process the bleed air through multiple cycles of cooling/pressure reduction and compression/heating. Cooling and pressure reduction is accomplished with heat exchangers (including condensers) and with turbines (which also extract work from the bleed air), while compression/heating is accomplished with compressors and reheaters. Many systems include at least one heat exchanger that utilizes external air to cool the bleed air, with a heat exchanger fan commonly included for augmenting external flow in conditions when ram inlet flow is not available. 
         [0004]    Air cycle-based aviation ECS systems are required to operate under a variety of conditions. Some of these conditions can involve exposure to airborne particulates, which can result in the accumulation of particulate debris on and around the heat absorption side of heat exchangers that use external air to absorb heat from the bleed air. Continued accumulation of such debris can ultimately lead to partial to complete or near-complete airflow blockage on the heat absorption side of the heat exchanger, which can result in reduced cooling performance, heat exchanger fan problems such as fan surge, broken fan blades, and system failure. Fan blade breakage can also involve failed journal bearings, turbine rotor rubs, and smoke events in the cabin. Other ECS components, including but not limited to turbines and compressors and their associated components, are also subject to wear and component breakage, which can also result in smoke events in the cabin. Smoke in cabin events are quite disruptive to flight operations, and can result in a disturbance to passengers, deployment of emergency equipment, and potential re-routing of flights. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    According to some aspects of the invention, an aircraft environmental conditioning system comprises an air cycle machine for conditioning an airflow comprising hot compressed air by reducing its temperature and pressure. The air cycle machine is disposed in a housing in an unpressurized area of the aircraft, and produces conditioned pressurized air for delivery to a pressurized area of the aircraft. The system also includes a vibration sensor disposed within the housing, and a controller in communication with the vibration sensor that is configured to respond to vibration detected by the vibration sensor. 
         [0006]    According to some aspects of the invention, a method of operating an aircraft environmental conditioning system comprises operating an air cycle machine disposed in a housing in an unpressurized area of the aircraft to condition hot compressed air by reducing its temperature and pressure to produce conditioned air pressurized air for delivery to a pressurized area of the aircraft. The method also includes monitoring output of a vibration sensor disposed within the air cycle machine. According to the method, an alert is generated is alerted in response to vibration detected by the vibration sensor. 
     
    
     
       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 FIGURE, which is a schematic representation of an aircraft environmental conditioning system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]    With reference to the FIGURE, the FIGURE schematically depicts an exemplary environmental air conditioning system  100  for an aircraft. The environmental air conditioning system  100  is inside housing  105  (only a portion of housing  105  is shown) disposed in an unpressurized area of an aircraft, separated from a pressurized area by bulkhead  110 . As shown in the FIGURE, compressed air  112  from a compressed air source (not shown) such as a turbine engine bleed, an APU bleed, or an electrically-powered compressor is delivered through control valve  114  and conduit  116  to heat exchanger  115  (also referred to in the art as a primary heat exchanger) where it rejects heat to ambient air flowing through or across a heat absorption side of heat exchanger  115 . Cooled compressed air is discharged from heat exchanger  115  to compressor  120 . A portion of the air going to heat exchanger  115  can be controllably diverted through conduit  117  and control/expansion valve  119  to mix with the outlet of turbine  144  and control the temperature of conditioned air  148 . Compressor  120  compresses its portion of the air from the heat exchanger  115 , which also results in heating of the air. The further compressed air is discharged from compressor  120  through conduit  124  to heat exchanger  126  (also referred to in the art as a secondary heat exchanger) where it rejects heat to ambient air flowing through or across a heat absorption side of heat exchanger  126 . 
         [0009]    The ambient air  113  flowing through or across the heat absorption sides of heat exchangers  115  and  126  can be a ram air flow from a forward-facing surface of the aircraft. In conditions under which insufficient airflow is generated by the forward motion of the aircraft for operation of the heat exchangers  115 ,  126 , the air flow can be assisted by operation of fan  128 . Check/bypass valve  129  allows for bypass of the fan  128  when ram air flow is sufficient for the needs of the heat exchangers  115  and  126 . Heat exchangers  115 ,  126  can share a flow path for the ambient cooling air, and can be integrated into a single unit with heat exchanger  115  sometimes referred to as a primary heat exchanger and heat exchanger  126  sometimes referred to as a secondary heat exchanger. Cooled air discharged from heat exchanger  126  is delivered through conduit  132  to a heat rejection side of heat exchanger  130 . In the heat rejection side of heat exchanger  130 , the air is further cooled to a temperature at or below the dew point of the air and flows into water removal unit  135  where liquid water  136  condensed from the air is removed. The dehumidified air flows through a heat absorption side of heat exchanger  130  where it is re-heated before being delivered through conduit  138  to turbine  140 , where work is extracted as the air is expanded and cooled by turbine  140 . A portion of the air going to turbine  140  can be diverted by valve  141  if needed to allow the temperature of the air at the inlet to the heat absorption side of heat exchanger  130  to be above freezing. The cooled expanded air discharged from the turbine  140  is delivered through conduit  142  to a heat absorption side of heat exchanger  130  where it along with the dehumidified air discharged from water collection unit  135  provides cooling needed to condense water vapor from air on the heat rejection side of heat exchanger  130 . The air streams on the heat absorption side of the heat exchanger  130  are thus reheated. Heat exchanger  130  is also sometimes referred to as a condenser/reheater, and can be integrated with water removal unit  135  in a single unit. The reheated air from conduit  142  exiting from the heat absorption side of heat exchanger  130  flows through conduit  143  to turbine  144 , where it is expanded and cooled, and then discharged from the system  100  through conduit  145  as conditioned air  148  to provide conditioned air to a cooling load, for example, the cabin of the aircraft. A check valve  146  at the bulkhead  110  prevents outflow from the pressurized area of the aircraft through the environmental air conditioning system  100  during flight when the system  100  is not being operated. 
         [0010]    The environment air conditioning system  100  also includes a power transfer path  147  such as a rotating shaft that transfers power to the compressor  120  and fan  128  from work extracted by turbines  140  and  144 . The moving parts associated with the power transfer path  147  as well as the moving parts and any parts that contact moving parts (e.g., bearings, bushings, supports, housings, vanes, blades, etc.) of any or all of the compressor  120 , fan  128 , or turbines  140  and  144  can be a source or contributing factor to catastrophic system failure that can result in a cabin smoke event. For example, over time the heat absorption side of the heat exchangers  115  and  126  can become clogged with airborne debris from inlet air  113 . When this happens, the fan blades of fan  128  are subject to unexpected stress because sufficient air is not provided through the heat exchangers  115 ,  126  for smooth aerodynamic operation of the fan blades. If the blockage goes undetected, one or more fan blades can break, resulting in a bearing failure that generates smoke that is blown by the air cycle machine into the aircraft cabin. 
         [0011]    As shown in the FIGURE, the environmental conditioning system  100  can be equipped with one or more vibration sensors such as any one or more of exemplary vibration sensors  152 ,  154 ,  156 , or  158 . By monitoring vibration or other motion of moving components in the air cycle machine and non-moving components in proximity to such moving components, unexpected or abnormal vibration or other motions can be detected that are indicative of an impending or actual equipment failure. A controller  160  is shown in the FIGURE, which is in communication (e.g., wireless communication, wired communication, or both wired and wireless communication) with the sensor(s)  152 ,  154 ,  156 ,  158 , and can also be in communication with various other system components (e.g., electrical switches, pressure sensors, temperature sensors, flow sensors, control valves, etc.). The controller can be located inside or outside of the housing  105 , and can be a local controller networked with other controllers or an aircraft systems controller, or can integrated with the system level controller. As shown in the FIGURE, each of the vibration sensors  152 ,  154 ,  156 , and  158  is positioned in contact with or proximate to each of the rotating devices fan  128 , compressor  120 , turbine  140 , or turbine  144 , respectively and can therefore provide information to the controller  160  that is specific to identify the device exhibiting problems. The vibration sensors can be any of a variety of known types of sensors, including but not limited to velocity sensors or proximity sensors. In some embodiments, the vibration sensors are accelerometers. Because an accelerometer provides a stream of data of the g-forces acting on it, the accelerometer readout can be used to detect not only vibration intensity, but also patterns in vibration or motion of components such as a cavitation pattern for fan  128  indicative of insufficient airflow through the heat absorption side of heat exchangers  115 ,  126 . The accelerometers g-force reading can also be utilized to determine the rotational velocity (i.e., rotations per minute) of turbine  140 , turbine  144 , compressor  120 , fan  128 , or the power transfer path  147 . Rotational velocities outside of a normal range (e.g., 10,000-50,000 rpm) can be indicative of impending or actual equipment failure. 
         [0012]    In operation, the specific criteria used by the controller  160  to identify abnormal device operation will vary based on the specifics of the equipment and system design, but can be determined by experimentation with simulated failures. For example, the output of vibration sensor  152  associated with fan  128  can be observed under conditions where the heat absorption side of heat exchangers  115 ,  126  is purposely blocked to varying degrees, and the observed data can be used to set conditions for the controller  160  to identify anomalous data during operation of the system. Some equipment failure modes can provide detectable vibrational or motion signatures in advance of actual failure (i.e., impending failure) or at the onset of failure (i.e., actual failure), allowing for the provision of an alert to flight crew or maintenance personnel in advance of any equipment failure. For example, a blocked heat exchanger  115 ,  126  can cause cavitation, the vibrational or motion signature of which can be detected by an accelerometer. Cavitation can lead to fan blade breakage, which can rapidly lead to a smoke-producing bearing failure or equipment overheat. Fan blade breakage can also be detected based on the output characteristics from the vibration sensor  152  as an onset of equipment failure. Another failure mode detectable by vibration sensors is a bearing failure. A vibration sensor attached to or proximate to a bearing housing can detect impending bearing failure through vibration. At the onset of catastrophic smoke-producing equipment failure, a vibration sensor attached to or proximate to a bearing housing can detect a telltale vibration signature. 
         [0013]    In some embodiments, a first type of alert of impending equipment failure is made based on a first set of output criteria from the vibration sensor(s), and a second type alert is made at the onset of equipment failure based on a second set of output criteria from the vibration sensor(s). Of course, multiple sets of criteria can be utilized to generate multiple types of alerts. In some exemplary embodiments, the controller  160  can be configured to provide an alert to the flight crew initiate a changeover to a parallel onboard air cycle machine or to descend to an altitude where cabin pressurization is not needed, thus limiting or avoiding equipment damage. Alternatively, the controller can automatically initiate a changeover to a parallel air cycle machine. An alert can also be made to ground maintenance personnel to inspect and service the heat exchanger airflow assembly, replacing any components that show signs of damage or that data collected by controller  160  indicate has been subjected to conditions that could cause undetectable damage to components (e.g., metal fatigue in fan blades). The same control options exist at the failure onset stage (e.g., alerting flight crew, automatically shutting down equipment and starting up a parallel onboard air cycle machine, or leaving an alert or data trail for ground-based maintenance personnel), of course with greater urgency for shutting down equipment. Even at the onset of equipment failure, pro-active detection at the source of the equipment failure can provide a valuable head start for any measures take to prevent smoke from entering the aircraft cabin, compared to the previous approach of waiting until smoke is smelled or observed already in the cabin. 
         [0014]    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.