Abstract:
A cabin pressure control apparatus that has an outflow valve that operates with a reference chamber without the need of using bleed air from the aircraft engines to adjust the pressure within the reference chamber. The invention has only pneumatic connections and no electrical connections to the outflow valve. Intrinsic negative differential protection is provided. Control solenoid(s) and pump(s) are internal to the controller for protection and simplified interconnection. The apparatus can be easily fitted in the aircraft without requiring additional cockpit panel space. The aircraft pressurization control apparatus is fully backward compatible with existing pressurization control systems as currently being manufactured by Kollsman, Inc.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to aircraft pressurization control systems, in particular, mechanisms which regulate the flow of air from and into the cabin to maintain cabin pressure within prescribed limits.  
       BACKGROUND OF THE INVENTION  
       [0002]     A number of devices have been proposed which are designed to regulate the cabin pressure of an aircraft as the aircraft ascends and the ambient pressure decreases. Due to the physiological requirements of the passengers, the cabin pressure under any conditions must not be permitted to fall below that what would be experienced by a mountain climber at an altitude of 15,000 feet. Even under those emergency conditions, passengers and crew can experience hypoxia and mountain sickness. Therefore, modern business aircraft have a maximum set cabin altitude of approximately 8,000 feet to maintain a comfortable margin of safety.  
         [0003]     Ideally it would be preferable to maintain cabin pressure at or near sea level irrespective of the actual altitude of the aircraft. However, pressure differentials between the cabin and the ambient pressure would require the aircraft to be so robust as to be impractical. Therefore, aircraft manufacturers generally design their craft to have a maximum pressure differential of no more than approximately 8½ to 9½ psi. This design specification enables business jets to operate at reasonable cruise altitudes yet maintain comfortable cabin pressure conditions.  
         [0004]     Environmental air conditioning systems using bleed air from the aircraft engines introduce fresh air from the outside so that occupants are comfortable and not breathing the same air over and over again during the flight. Business jet aircraft such as Cessna Citation CJ1, CJ2, Bravo, Encore and Excel Aircraft typically fly at a cruise altitude of about 30,000 feet to 40,000 feet more or less depending on traffic and weather conditions.  
         [0005]     Outflow valves such as those made by Kollsman, Inc. of Merrimack, N.H. utilize an internal reference chamber that, in combination with a solenoids and bleed air from aircraft engine(s) to control the reference chamber, pressurizing the aircraft. Depending on the pressure within the reference chamber relative to the cabin pressure and ambient pressure, the outflow valve will either allow air to exit from the cabin faster than the airflow into the cabin (such as required when the aircraft is ascending) or air to exit from the cabin slower than the airflow into the cabin (such as required during descending). While these valves are extremely reliable and enable the aircraft to maintain a comfortable cabin pressure during the operating envelope of the aircraft, the bleed air from the engine typically contains a number of contaminants. This includes, water, iron particles (rust), and petrochemicals. These contaminates can build up over time in the solenoid (the magnetics hold the rust) and cause a fault in the system.  
         [0006]     A cabin pressure control apparatus that has an outflow valve that operates with a reference chamber without the need of using bleed air from the aircraft engines to adjust the pressure within the reference chamber; has only pneumatic connections and no electrical connections to the outflow valve; provides intrinsic negative differential protection; has control solenoid(s) and pump(s) that are internal to the controller for protection and simplified interconnection and has been easily fitted in the aircraft without requiring cockpit panel space is not found in the prior art.  
       SUMMARY OF THE INVENTION  
       [0007]     It is an aspect of the invention to provide an aircraft pressurization control apparatus that will pneumatically regulate the flow of exhaust air from an aircraft cabin.  
         [0008]     It is another aspect of the invention to provide an aircraft pressurization control apparatus that provides two or more identical outflow valves.  
         [0009]     Another aspect of the invention is to provide an aircraft pressurization control apparatus that utilizes at least one miniature pump that is used to inflate or deflate a reference chamber that is positioned within an outflow valve.  
         [0010]     It is still another aspect of the invention to provide an aircraft pressurization control apparatus to incorporate at least one miniature pump within the controller of the aircraft pressurization control apparatus.  
         [0011]     Another aspect of the invention is to provide an aircraft pressurization apparatus that uses only pneumatic connections between the outflow valve and the controller.  
         [0012]     It is an aspect of the invention to provide an aircraft pressurization control apparatus that has one controller for a pair of two or more identical outflow valves.  
         [0013]     Another aspect of the invention is to provide an aircraft pressurization control apparatus that uses one pump and one solenoid to inflate the reference chambers of the respective outflow valves and a vacuum pump and its solenoid to deflate the reference chambers of the respective outflow valves.  
         [0014]     It is still another aspect of the invention to provide an aircraft pressurization control apparatus that has the inflation pump and solenoid pneumatically connected to the aircraft cabin and the vacuum pump and its solenoid to the ambient air outside of the aircraft cabin.  
         [0015]     It is another aspect of the invention to provide an aircraft pressurization control apparatus that is full backward compatible with the existing pressurization control system manufactured by Kollsman.  
         [0016]     Finally, it is aspect of the invention to provide an aircraft pressurization control apparatus that eliminates the need for using bleed air from the aircraft engines in order to operate the reference chambers of the outflow valves of the aircraft pressurization control system.  
         [0017]     These and other aspects of the invention will become apparent in light of the detailed description of the invention which follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is an illustration of the aircraft pressurization control apparatus in accordance with the invention.  
         [0019]      FIG. 2  is an isometric view of the controller of the apparatus.  
         [0020]      FIG. 3 . is an isometric view of an outflow valve of the apparatus.  
         [0021]      FIG. 4  is top view of the controller housing with the cover removed showing the placement of the solenoids and miniature pumps in the preferred embodiment.  
         [0022]      FIG. 5  is a cross-sectional view of the outflow valve showing the reference chamber diaphragm.  
         [0023]      FIG. 6  is an illustration of the surface area of the diaphragm showing the cabin annular area relative to the ambient annular area.  
         [0024]      FIG. 7  is an illustration of the controller pumps and solenoid connections in the preferred embodiment.  
         [0025]      FIG. 8  is an illustration of an alternative embodiment for the controller pneumatic connections using only the inflation pump with the solenoids.  
         [0026]      FIG. 9  is an illustration of another alternative embodiment showing the use of one reversible pump connected in series to a solenoid on the cabin flow side of the controller mechanism.  
         [0027]      FIG. 10  is an illustration of still another alternative embodiment showing the use of one reversible pump connected in series to a solenoid on the ambient air side of the controller mechanism.  
         [0028]      FIG. 11  is an illustration of another alternative embodiment showing the use of one reversible pump connected in parallel to a solenoid on the cabin air flow side of the controller mechanism.  
         [0029]      FIG. 12  is another illustration of an alternative embodiment using a single vane or centrifugal pump.  
         [0030]      FIG. 13  is an illustration of an alternative embodiment using a single reversible pump.  
         [0031]      FIG. 14  illustrates an embodiment of the invention using two pumps connected in parallel in order to increase the maximum flow rates. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     The cabin pressurization control apparatus includes two identical outflow valves  12  as shown in  FIG. 1 . Valves  12  pneumatically regulate the flow of exhaust air from the cabin  18 , and require no electrical power to operate. Each self-regulating outflow valve is constructed with a reinforced fluorosilicone diaphragm covering an outlet grill. The diaphragm is larger than the grill by an amount that makes the annular area approximately equal to the grill area. Cabin pressure pushes against the annular outer area of the diaphragm, trying to open the outflow port. The lower pressure outside the aircraft structure draws the diaphragm against the grill trying to close the port.  
         [0033]     Above the diaphragm is a sealed reference pressure chamber. The air trapped in this chamber functions as the regulating “spring” which determines the operating point of the valve. The KAPS II controller contains two Solenoid pilot valves that are driven by the controller electronics to change the reference chamber pressure. These solenoids connect either cabin air or outside static air to the reference chamber to change its internal pressure. Changes in reference chamber pressure cause the diaphragm to move, which either increases or decreases the outflow rate from the cabin, thereby changing the cabin pressure and equivalent altitude. A common pneumatic connection between outflow valve reference chambers ensures balanced outflow between valves.  
         [0034]     The valve geometry is such that the pressure in the reference chamber always lies midway between the cabin air pressure and the ambient static air pressure. During flight, the static air outside the aircraft is at a lower pressure than the air in the aircraft cabin. This allows the reference chamber to be inflated by the cabin pressure regulated by a solenoid and deflated by using ambient pressure regulated by a solenoid. When the aircraft is on the ground, there is almost no difference between the ambient pressure and cabin pressure.  
         [0035]     Typically in prior art devices, bleed air from the engines is used to increase the reference chamber pressure in this situation. This bleed air is also connected to a venturi vacuum ejector to create a lower pressure to decrease the reference chamber pressure when necessary on the ground. The present invention eliminates the need for using engine bleed air.  
         [0036]     Each valve  12  is self-regulating having maximum safety limiting valves  30 ,  32 . Safety valve  30  checks for maximum differential pressure and safety valve  32  checks for maximum equivalent cabin altitude. The limits for these valves are factory set and adjusted to the individual aircraft requirements. Typically, the altitude safety valve  32  is set from 13,000 to 15,000 feet to prevent the aircraft occupants from experiencing high altitude problems. The maximum differential pressure safety valve  30  is set so the pressure differential between the cabin and the ambient conditions does not exceed a limit specified by the aircraft manufacturer (typically from 8½ psi to 9½ psi) to prevent overstressing the structural integrity of the aircraft. The safety valves override any settings provided by the controller  10  to the outflow valves  12 .  
         [0037]     Optionally, manual toggle valve  14  (well known in the art) can be included which provides full manual control of cabin pressure in the event of electrical power failure. The valve  14  is typically a three-position valve with a return spring to center position which will supply static pressure (climb) or cabin (descent) pressure to the outflow valves  12 .  
         [0038]     As can be seen, all connections to valves  12  from controller  10  are pneumatic.  
         [0039]     All control and communications interface with the aircraft is accomplished via the aircraft ARINC 429 electronic data bus via connection port  28 . For convenience, the system also provides for a number of discrete electronic inputs, which may be used in place of the ARINC inputs at the discretion of the aircraft manufacturer. The ARINC interface is bi-directional, and the operation of the controller  10  is coupled very closely to the integrated aircraft Avionics system, all of which are well known in the art.  
         [0040]     Controller  10  measures cabin pressure using its own internal transducer  33  as shown in  FIGS. 7-13 . The bi-directional ARINC interface provides both cabin pressure and cabin pressure rate outputs to the aircraft avionics system. In addition, the controller  10  has an internal pressure transducer  31 , which is used to directly measure cabin differential pressure. This enables the controller to provide this information to the aircraft avionics system as well. In addition, the internal differential pressure transducer  31  allows the apparatus to maintain full autoschedule operation if the Aircraft ARINC 429 bus communication is lost. The need to fallback to isobaric control is therefore eliminated.  
         [0041]     Outflow valves  12  are bolted to the cabin wall bulkhead  16  so that the open bottom grill is exposed to the outside of the aircraft. Housing  15  of controller  15  is attached inside of the cabin  18  of the aircraft wherever it is convenient. Nameplate  13  provides manufacturer information.  
         [0042]     All the pressure lines shown are preferably ¼ tubing connected via ¼″ NPT fittings or barb-type fittings. Line  72  connected to fitting  38  provides airflow to the reference chamber  48 . Line  80  measures the static pressure outside of the aircraft. Port  84  permits air to enter from the cabin. Port  82  measures the cabin air pressure. Line  78  permits airflow from the reference chamber  48  to exit the aircraft. The operation of valves  12  is discussed below.  
         [0043]      FIG. 2  shows an isometric view of the preferred embodiment of the housing  15  of controller  10 . Controller  10  has an extremely small footprint, preferably measuring 6 inches by 6 inches and being about 3 inches high, thus making it easy to install virtually anywhere within the aircraft. Estimated weight is only about 2½ pounds.  
         [0044]      FIG. 3  depicts an isometric view of the preferred embodiment of an outflow valve. Similarly, these valves have a small footprint, being about 7 inches in diameter overall in one embodiment and only about 5½ inches high. Estimated weight of each outflow valve  12  is about 1¾ pounds. The overall grill diameter of the valves is chosen to match the expected maximum inflow rate of air provided to the cabin by the aircraft environmental control system. Smaller aircraft typically use a 3 inch diameter valve. Larger aircraft may require a 4 inch or larger diameter valves.  
         [0045]      FIG. 4  is a top view of the controller  10  housing  15  with the cover removed showing the placement of the solenoids and miniature pumps in the preferred embodiment. The transducers  31 ,  33  as well as the pneumatic connections plus electronic circuit board and other electrical connections have been removed to more clearly illustrate how the tubing is connected between the fittings, solenoids  44 ,  45  and miniature pumps  42 ,  43 . Also, note the arrows in the tubing indicates the direction of airflow when controller  12  in operation (discussed below).  
         [0046]     The miniature pumps  42 ,  43  are used to provide the pneumatic control to the outflow valves  12  during periods when the cabin to static differential pressure is low, i.e. primarily take-off and landing. This saves the engines from having to supply service air, which allows higher thrust output during take-off. It also allows the outflow valve  12  to be commanded to full open without the engines, which reduces the bump associated with engine turn on with the doors closed. The plumbing associated with the service air is also eliminated; reducing aircraft design complexity and aircraft weight. Placing miniature pumps  42 ,  43  in the controller  10  reduces the number of pneumatic connections, reducing the risk of misconnected hoses and connector failures.  
         [0047]     The automated switchover of pumped air to static or cabin air allows the pumps  42 ,  43  to be used for only short periods of time. The pumps  42 ,  43  are needed during ground testing of the system, during take-off, landing, decompression, and when the differential pressure between static and cabin air is below 0.2 in. Hg.  
         [0048]     As shown, pumps  42 ,  43  are physically located next to the solenoids  44 ,  45  in the controller housing allowing the solenoids  44 ,  45  to heat the pumps  42 ,  43  and reduce the possibility of icing. As noted above, pumps  42 ,  43  are only turned on during take-off, final approach, ground test, and decompression. With a rated mean-time-before-fault (MTBF) of 10,000 hours of operation, assuming 4 flights per day, the calculated pump life would be greater than 70 years.  
         [0049]     Pumps  42 ,  43  are preferably rotary vane pumps, such as made by Thomas Industries. However, any pumps than can generate more than 0.2 PSI pressure can be used. Maximum pump flow rate and the specific outflow valves used affect the maximum time for system pre-pressurization, which occurs at take-off. The pumps can also be a diaphragm pump (necessary in  FIG. 12  embodiment), such as made by Thomas Industries. The pumps can be any combination of single or dual headed pumps such that only pressure or pressure and vacuum are generated. Any pump that can inflate or deflate the manifold is suitable.  
         [0050]     The preferred solenoids  44 ,  45  are a 2-way normally closed configuration, such as sold by Precision Dynamics. Solenoids  44 ,  45  need to be able to open and close at least twice as fast as the bandwidth of the system control loop. Further, solenoids  44 ,  45  must be able to handle two times the maximum pressure seen by the pressurization control apparatus (1 Atmosphere). A three-way solenoid (not shown) may be used to replace the function of two solenoids. A three way solenoid has a lower reliability due to continual switching to modulate the manifold pressure. A four-way solenoid could also be used to replace the two 2-way solenoids, while maintaining the same pneumatic connections.  
         [0051]     As shown in  FIG. 5 , the reference chamber  48  of outflow valve  12  is shown. When cabin  18  is pressurized during flight, the cabin  18  pressure is substantial greater than the outside pressure  20 . Thus, diaphragm  64  preferably made from reinforced fluorosilicone covers a three-inch diameter outlet grill  74 . The diaphragm  64  is larger than the grill by an amount that makes the annular area approximately equal to the grill area (See,  FIG. 6 ). Cabin pressure pushes in direction  67  against the annular outer area of the diaphragm, trying to provide opening  65  of the outflow port; the lower pressure outside the aircraft structure (aircraft altitude) draws the diaphragm  64  against the grill (line  64 ′) trying to close the port.  
         [0052]     Above the diaphragm  64  is a sealed reference pressure chamber  48 . The air trapped in this chamber functions as the regulating “spring” which determines the operating point of the valve. Solenoid pilot valves and pumps in the controller  10  are modulated by the controller to change the reference chamber pressure. Changes in reference chamber pressure cause the diaphragm  64  to move, which either increases or decreases the outflow rate from the cabin, thereby changing the cabin pressure and altitude. A common pneumatic connection  72  between outflow valve reference chambers ensures balanced outflow between valves.  
         [0053]     Each outflow valve  12  features an independent maximum differential pressure safety relief valve  30  connected to static pressure via line  80  and cabin pressure via port  24 , and a maximum altitude safety limit valve  32  connected to the cabin pressure via port  24 .  
         [0054]     If the differential pressure becomes too great, spring adjusted plunger  58  changes the pressure in the reference chamber  48  to keep the aircraft operating within the prescribed limits. Similarly, if the maximum altitude pressure exceeds the limits, spring adjusted plunger  60  adjusts the reference chamber  48 .  
         [0055]     Isolation is provided between outflow valves  12  to prevent a single fault from disabling both maximum differential pressure valves. This is implemented via a 0.033 diameter restrictor orifice (not shown) at each of the outflow valve common ports. Together, these outflow valves meet all applicable regulations regarding maximum and negative differential pressure; no additional safety valves are required.  
         [0056]     The forward pressure drop for a single outflow valve will not exceed 0.25 psid at 16 lb/min flow, which equates to 0.7 inches of water at 10 ppm for two outflow valves in parallel.  
         [0057]     The grill  74  is TEFLON coated to avoid tobacco tar accumulation. Tar accumulation on the smooth fluorosilicone diaphragm is minimal. Should any foreign matter intrude into the grill-sealing surface, the flexible diaphragm  64  conforms to it and continues to operate normally. Field history for the apparatus shown reveals that the grill  74  does not create objectionable noises during operation. The grill  74  has a 3.5″ diameter bolt circle for aircraft bulkhead mounting.  
         [0058]      FIG. 6  is an illustration of the surface area of the diaphragm  64  showing the cabin annular area  68  relative to the ambient annular area  70 . Rib  62  is provided to help stiffen diaphragm  64  so that it can more effectively provide seal  65 . Area  68  is equal to area  70  so that the pressure within reference chamber  48  is the midpoint (numerical average) of the cabin pressure and the ambient pressure.  
         [0059]     As shown in  FIG. 7 , which depicts the preferred embodiment, pump  42  is connected in series with solenoid  44 . The input to pump  42  is connected to line  84  which in turn is connected to the cabin of the aircraft. The output of solenoid  44  is connected to line  72  which is connected to the reference chamber  48  of the outflow valve assembly  12 . Pump  42  pumps air from the cabin to pressurize the reference chamber  48 .  
         [0060]     Pump  43 , also connected in series with the solenoid  45  enables reference chamber  48  to be deflated via line  72  through static pressure line  78  which exits the aircraft.  
         [0061]     During flight, pumps  42  and  43  are not used. Solenoid  44  which is connected to the cabin air is used during descent and solenoid  45  which is connected to the ambient air is used during climbing. Recall that the pressure in reference chamber  48  is the midpoint (numerical average). Thus, if the plane is descending, the ambient pressure is increasing and the reference chamber pressure must also increase so that the reference pressure is midpoint between the cabin pressure and ambient pressure. Similarly, if the plane is climbing, the ambient pressure is decreasing and reference pressure must also decrease correspondingly so that air in the reference chamber is permitted to exit the aircraft via pressure line  78 . In this manner, the electronic circuitry of controller  10  modulates the opening and closing of solenoids  44  and  45  to maintain cabin pressure within the prescribed operating envelope.  
         [0062]     Note that air is constantly being brought into the cabin via the environmental air control system (not shown) to provide a supply of fresh air in the cabin. Thus, outflow valve assembly  12  is never fully closed during flight.  
         [0063]     When the aircraft is on the ground or landing, the pressure differential across diaphragm  64  is insufficient to provide the degree of control necessary. The solenoid  44 ,  45  merely function as “on or off” switches and passively regulate airflow due to the pressure gradient between cabin and ambient outside air.  
         [0064]     Thus, pump  42  raises the pressure in reference chamber  48  and pump  43  lowers the pressure in reference chamber  48 . Solenoid  44  must be open when pump  42  is on and solenoid  45  must be closed. This is the landing mode. Similarly, solenoid  45  must be open when pump  43  is on and solenoid  44  must be closed. This is the take off mode.  
         [0065]     When the aircraft is on the ground and powered and controller  10  senses that a take-off sequence has been initiated, pre-pressurization of the cabin commences to an altitude of 200 feet below the present altitude and completes in 30 seconds. This is accomplished by activating pump  43  increasing the pressure in the reference chamber  48 .  
         [0066]     As shown in  FIG. 8 , an alternative embodiment uses only pump  42 . Solenoids  44 ,  45  operate the same as shown in  FIG. 7 . Thus, active flow of air (provided by a pump) due to controller  10  is only possible during descent. While this configuration does not provide the degree of control present in the preferred embodiment, this arrangement is acceptable.  
         [0067]      FIG. 9  depicts still another embodiment using a single reversible pump  41  on the “cabin” (descent) side of controller  10 . Again, solenoids  44 ,  45  work the same as in the previous embodiments. Using a reversible pump  41  enables air to be pumped into and out of reference chamber  48  so that both take-off and landing pressurization control is more effectively provided. However, the use of single pump does not provide the redundancy obtained with separate descent and climb pumps.  
         [0068]      FIG. 10  is a variation of the embodiment shown in  FIG. 9 , only the reversible pump  41  is placed on the “ambient” (climb) side of controller  10 . As before, the solenoid operation is the same.  
         [0069]      FIG. 11  shows still another location for pump  41 . In this embodiment, both solenoids  44  and  45  are closed when pump  41  is pressurizing reference chamber  48 . When deflating reference chamber  48 , solenoids  44 ,  45  are also closed. Pump  41  when deflating chamber  48  must pump against a pressure gradient as the cabin pressure is going to be higher than the reference chamber pressure.  
         [0070]      FIG. 12  shows an embodiment that utilizes just a single pump  42  without the use of solenoids. In this embodiment, pump  42  must be a vane pump so that when pump  42  is turned off, air can escape (small arrows in line  84 ) from reference chamber  48 . Note that only limited control is possible during take-off until the ambient pressure is sufficiently low to provide a pressure gradient from inside to outside of the cabin.  
         [0071]     This embodiment is similar to that shown in  FIG. 12  only a single reversible pump  41  replaces pump  42 . In this configuration, both ascent and descent, take-off and landing control is provided. However, pump  41  must be working constantly so that the reliability of this embodiment is less than the preferred embodiment. Further, this embodiment lacks the redundancy of parts provided with the preferred embodiment. The embodiment shown illustrated in  FIG. 14  shows two pumps,  42  and  42 ′ connected in parallel in order to increase the maximum flow rates from the cabin to said reference chamber  48 .  
         [0072]     While certain representative embodiments of the invention have been described herein for the purposes of illustration, it will be apparent to those skilled in the art that modification therein may be made without departure from the spirit and scope of the invention.