Patent Publication Number: US-8991297-B2

Title: Compressors with improved sealing assemblies

Description:
TECHNICAL FIELD 
     The present invention generally relates to compressors, and more particularly relates to high temperature and high pressure sealing assemblies in compressors. 
     BACKGROUND 
     Air recharge systems (ARS) are designed for use in aircraft applications. For example, the ARS may be used, in flight or on the ground, to recharge air bottles of a stored energy system to high pressures, such as 5000 psig and above. As such, a typical ARS uses a compressor with a number of stages to compress air to the desired pressures. 
     Generally, o-ring type seals are employed in piston or rod sealing applications, such as within compressors, to provide a seal between two adjacent cylindrical surfaces. These seals are subjected to various external forces and conditions throughout such use. At low pressure and low temperature conditions, seals may accommodate non-uniform pressure distribution due to the nature of their resilient, flexible and elastic compositions. Seals subjected to high pressure, for example, greater than about 3000 psig, and high temperatures, for example, greater than about 300° F., tend to deform, and gradually extrude into, for example, the sealed gap between the adjacent cylindrical surfaces. In addition, elevated temperatures eventually may reduce the physical qualities of resilient, flexible, and elastic materials. As such, these types of seals may need to be replaced at an undesirable frequency and/or leakages may occur, thereby reducing the efficiency and service life of the compressors. 
     Engineers have attempted to design more robust seals by redesigning the shape, increasing or decreasing the diameters and thicknesses, and the like, or by altering the compositions in order to improve the ability to withstand higher temperatures and pressures and to increase the service life of the seal. While these designs have met with some success, improvements to conventional sealing assemblies in applications such as high temperature and high pressure compressors are desired. 
     Accordingly, it is desirable to provide improved sealing assemblies, particularly sealing assemblies for compressors. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
     BRIEF SUMMARY 
     In accordance with an exemplary embodiment, a compressor includes a housing; a compressor liner positioned within the housing and at least partially defining a first cylinder with an inlet and an outlet; a piston positioned within the first cylinder and configured to compress air flowing into the first cylinder through the inlet; a cylinder head at least partially defining the first cylinder; and a sealing assembly for sealing an interface between the compressor liner and the cylinder head. The sealing assembly includes a ring seal at an interface between the cylinder head and the compressor liner; a vent port on an opposite side of the ring seal from the first cylinder; and a vent tube extending between the vent port and the inlet such that air leaking through the ring seal from the first cylinder flows through the vent port, through the vent tube, and into the inlet. 
     In accordance with an exemplary embodiment, a sealing assembly is provided between a first component and a second component of a compressor with a cylinder having an inlet and an outlet. The assembly includes a ring seal between the first component and the second component at the outlet of the compressor; a vent port defined by the first component and at least partially sealed by the ring seal from air compressed within the cylinder; and a vent tube extending between the vent port and the inlet such that any portion of the air that leaks through the ring seal flows through the vent port, through the vent tube, and into the inlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a cross-sectional view of a high pressure, high temperature compressor incorporating a sealing assembly in accordance with an exemplary embodiment; 
         FIG. 2  is a partial cross-sectional view of the sealing assembly of  FIG. 1  in accordance with an exemplary embodiment; and 
         FIG. 3  is a more detailed cross-sectional view of a portion of the sealing assembly of  FIG. 2  in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description. 
     Broadly, exemplary embodiments discussed herein provide a sealing assembly for a high pressure compressor, such as a four stage compressor of an aircraft air recharge system. A number of o-rings may be provided between the compressor liner and compressor housing. Additionally, a c-seal is provided in a recess at an interface between the housing, the compressor liner, and the cylindrical head in the fourth stage of the compressor. A vent may be provided to prolong the life of the c-seal and to prevent leaks from flowing into undesirable areas. Additionally, the vent may be fluidly coupled to the inlet of the fourth stage such that any air leaking through the c-seal is vented back into the fourth stage and such that the pressure differential across the c-seal is reduced, thereby improving the efficiency of the compressor and further improving the service life of the c-seal. 
       FIG. 1  is a cross-sectional view of a high pressure, high temperature compressor  100  incorporating a sealing assembly  200  in accordance with an exemplary embodiment. In one exemplary embodiment, the compressor  100  may be used in an air recharge system (ARS) designed for use in aircraft applications. For example, the ARS may be used, in flight or on the ground, to recharge air bottles of a stored energy system to about 5000 psig. In one exemplary embodiment, the aircraft and/or a pilot will evaluate the pressure and temperature to determine 100% propellant in the recharge air bottles. As described below, the compressor  100  is a four stage compressor, although the sealing assembly  200  may also be incorporated into a compressor with any number of stages and/or other high pressure applications. 
     The compressor  100  generally includes a housing  102  that houses a drive shaft  104  and a compressor liner  120 . The compressor liner  120  defines four cylinders  130 ,  140 ,  150 , and  160  that respectively decrease in size to sequentially compress air in stages, as described below. The compressor liner  120  and housing  102  may be formed from any suitable material, such as heat treated stainless steel or iron. 
     The drive shaft  104  includes an eccentric circular lobe  106  and is supported on ball bearings  108 , perpendicular to an axis  110  of the cylinders  130 ,  140 ,  150 , and  160 . The drive shaft  104  may be coupled to and driven by a motor  112  mounted to the housing  102 . A piston assembly  170  is mounted on the drive shaft  104  at the eccentric circular lobe  106  via a slider  114  and a needle bearing  116 . The piston assembly  170  includes a yoke  172  extending through the cylinders  130 ,  140 ,  150 , and  160 . Pistons  132 ,  142 ,  152 , and  162  are mounted on the yoke  172  in the cylinders  130 ,  140 ,  150 , and  160  and are reciprocally driven in a linear motion when the drive shaft  104  is rotated, as discussed below. 
     More specifically, the first cylinder  130  corresponds to the first stage  280  of the compressor  100 . When the first piston  132  is in a withdrawn position (e.g., to the left in the view of  FIG. 1 ), air may enter the first cylinder  130  through an inlet  134 . The air is compressed within the compressor liner  120  as the piston  132  moves through the cylinder  130  to the other side of the first cylinder  130  (e.g., the position generally shown in  FIG. 1 ), e.g., the air is compressed between the piston  132  and compression liner  120  as the piston  132  reduces the available volume of the first cylinder  130 . The air leaves the first cylinder  130  via an outlet  136 , which is fluidly coupled to an inlet  144  of the second stage  282 . 
     The second cylinder  140  corresponds to the second stage  282  of the compressor  100 . When the second piston  142  is in a withdrawn position (e.g., the position generally shown in  FIG. 1 ), air may enter the second cylinder  140  through the inlet  144 . The air is compressed within the compressor liner  120  as the piston  142  moves through the cylinder  140  (e.g., to the left in  FIG. 1 ), e.g., the air is compressed between the piston  142  and compression liner  120  as the piston  142  reduces the available volume of the second cylinder  140 . The air leaves the second cylinder  140  via an outlet  146 , which is fluidly coupled to an inlet  154  of the third stage  284 . 
     The third cylinder  150  corresponds to the third stage  284  of the compressor  100 . When the third piston  152  is in a withdrawn position (e.g., to the left in the view of  FIG. 1 ), air may enter the third cylinder  150  through the inlet  154 . The air is compressed within the compressor liner  120  as the piston  152  moves through the cylinder  150  to the other side of the cylinder  150  (e.g., to the position generally shown in  FIG. 1 ) e.g., the air is compressed between the piston  152  and compression liner  120  as the piston  152  reduces the available volume of the third cylinder  150 . The air leaves the third cylinder  150  via an outlet  156 , which is fluidly coupled to an inlet  164  of the fourth stage  286 . 
     The fourth cylinder  160  corresponds to the fourth stage  286  of the compressor  100 . When the fourth piston  162  is in a withdrawn position (e.g., as is generally shown in  FIG. 1 ), air may enter the fourth cylinder  160  through the inlet  164 . The air is compressed within the compressor liner  120  as the piston  162  moves through the fourth cylinder  160  (e.g., to the left in  FIG. 1 ) e.g., the air is compressed between the piston  162  and compression liner  120  as the piston  162  reduces the available volume of the fourth cylinder  160 . The air leaves the fourth cylinder  160  via an outlet (not shown) of the compressor  100 , which in this embodiment is fluidly coupled to an air bottle of the ARS. The fourth cylinder  160  may be capped by a cylinder head  180 . Various check valves may be provided, for example, incorporated into the inlets and outlets for to ensure proper operation of the compressor  100 . 
     As shown in  FIG. 1 , the cylinders  130 ,  140 ,  150 , and  160  have decreasing sizes such that the air is compressed to higher and higher pressures as the air works through the stages. Since consecutive stages are paired on opposite sides of the drive shaft  104  and since the pistons  132 ,  142 ,  152 , and  162  are driven on a common yoke  172 , each stage of the compressor  100  compresses a portion of air during a given cycle. In one exemplary embodiment, the air is provided to the first stage  280  at about 30 psig. The first stage  280  compresses the air to about 150 psig. The second stage  282  compresses the air to about 500 psig, and the third stage  284  compresses the air to about 1800 psig. Finally, the fourth stage  286  compresses the air to about 5000 psig. In other embodiments, the pressure from the fourth stage  286  may exceed 5000 psig, including pressures greater than about 6000 psig or about 7000 psig 
     The compressor  100  further includes a number of cooling passages  190 ,  192 ,  194 , and  196  that remove heat from the air as it is compressed. The cooling fluid may be, for example, liquid polyalphaolefin (PAO). The cooling fluid may circulate at about 200 psig and about 180° F., as an example. Although not discussed in greater detail, the compressor  100  may further include an oil lubrication system, a downstream oil separation and return system, and a water removal and air drying system for conditioning the air as it is compressed. 
     As described below, the sealing assembly  200  is provided within the compressor  100  to prevent or mitigate air or cooling fluid from leaking within the compressor  100 . Particularly, the sealing assembly  200  prevents or mitigates leakage at the interfaces between the compressor liner  120  and the housing  102  and between the compressor liner  120  and the cylinder head  180 . Leakage is primarily an issue in the fourth stage, e.g., where the pressures are the highest. The sealing assembly  200  is discussed in greater detail with reference to  FIG. 2 . 
       FIG. 2  is a partial cross-sectional view of the sealing assembly  200  of the compressor  100  of  FIG. 1  in accordance with an exemplary embodiment.  FIG. 2  particularly shows the second and fourth stages of the compressor  100 . As noted above, the sealing assembly  200  prevents or mitigates air or cooling fluid from leaking during the compression cycle. 
     As shown in the view of  FIG. 2 , the sealing assembly  200  includes a number of o-rings  210 - 216  to seal interfaces between the compressor liner  120  and the housing  102 . The o-rings  210 - 216  may be provided in recesses in the compressor liner  120  and may be supported by one or more back-up rings. In general, the o-rings  211 - 216  prevent or mitigate leakage between the compressor liner  120  and housing  102 , and the o-ring  210  prevents or mitigates leakage between the cylinder head  180  and housing  102 . 
     The o-rings  210 - 216  may be constructed from flexible, resilient materials or any other material possessing the physical qualities capable to withstand high pressures. For example, o-rings  210 - 216  may be formed of materials such as synthetic rubber compositions, elastomeric substances, particularly silicone based compositions, fluoropolymer based compositions, fluorosilicone based compositions, other plastics such as polyether etherketone, polyamides, polyimides, polyethersulfone, other hi-modulus plastic compositions, and the like, alone or in combination with one or more reinforcing materials and/or additives, such as plasticizers, thermal stabilizers, antioxidants, light stabilizers, flame retardants, lubricants, foaming agents, blowing agents, surfactants, metal stabilizers, organostabilizers, organometallic stabilizers, and the like. In one embodiment, the o-rings  210 - 216  may be a graphite reinforced fluoropolymer material, such as graphite reinforced Teflon®. 
     The sealing assembly  200  further includes a c-seal  230  at the interface between the compressor liner  120 , the housing  102 , and the cylinder head  180 . The c-seal  230  is positioned within a recess  232  defined between the cylinder head  180  and the compressor liner  120 . As shown in  FIG. 2  and in greater detail in  FIG. 3 , the c-seal  230  has a c-shaped cross-sectional shape that is formed as an annular ring. In one exemplary embodiment, the c-seal  230  is an internal pressure c-seal, and the recess  232  is a counter-bore recess. In other embodiments, other types of ring seals and recesses may be provided. The c-seal  230  may be resilient such that each side of the c-seal  230  is biased outward to fill the recess  232 . In general, the c-seal  230  may be any suitable diameter, height, thickness, coating or casing, and coating or casing thickness. For example, the c-seal  230  may be an alloy such as Inconel that is silver plated. However, in one particular embodiment, the c-seal  230  is used at the fourth stage  286  of the compressor  100  to withstand the operating conditions of the fourth cylinder  160 . An o-ring may be subject to extrusion between the sealed surfaces, which may lead to a shorter service life. 
     At most operating conditions, the c-seal  230  prevents leaks between sealed surfaces. However, at some conditions, the temperatures and pressures of the fourth cylinder  160  may be higher than which the c-seal  230  is typically designed, particularly considering the high speeds and resulting flexing and relaxing that the c-seal  230  undergoes during each cycle. If unaddressed, the c-seal  230  may lose effectiveness over time. As such, a vent port  240  is provided in the sealing assembly  200  to cooperate with the c-seal  230  to address these issues by reducing the stress on the c-seal  230  and/or by accommodating any leaks that do occur. In one exemplary embodiment, the vent port  240  is perpendicular to the axis  110  of the cylinders  130 ,  140 ,  150 , and  160 , although other arrangements may be provided. 
     Generally, the vent port  240  is designed to reduce the stress on the c-seal  230 . For example, at a predetermined pressure, air may leak across the c-seal  230  into the vent port  240 . As a result, repeated deformation of the c-seal  230  by the air pressure changes of the fourth cylinder  160  is reduced. This relieves some of the pressure and stress on the c-seal  230  in certain situations. The vent port  240  also provides more control over leaks at the c-seal  230 . In some instances, without a vent port, any air leaking across a c-seal may leak into undesired areas of the compressor. For example, the vent port  240  prevents leakage of air into the cooling passages. 
     The vent port  240  extends through the cylinder head  180  and is fluidly coupled to a vent tube  250  at the outer surface of the cylinder head  180 . The vent tube  250  extends to the inlet  164  of the fourth stage  286 . As such, the vent port  240  of the sealing assembly  200  is fluidly coupled to the inlet  164  of the fourth cylinder  160 . The vent port  240  may be any suitable size, for example, the vent port  240  may be approximately 0.029 inches to approximately 0.036 inches, depending on the size of the compressor  100  and operating conditions. As a result, any air that leaks across the c-seal  230  is returned to the compressor  100  as working fluid. Conventional seal vents typically vent leaked air to an ambient pressure and out of the compressor. 
     As a result, the sealing assembly  200  provides seals between the compressor liner  120 , housing  102 , and cylinder head  180 . The c-seal  230 , vent port  240 , and vent tube  250  enable sealing at high pressures, and even during leaks, return the air to the compressor  100 , thereby increasing the efficiency of the compressor  100  and the service life of the c-seal  230 . 
     Additional details about the sealing assembly  200  are shown in  FIG. 3 , which is a more detailed cross-sectional view of a portion  300  of the sealing assembly  200  of  FIG. 2  in accordance with an exemplary embodiment.  FIGS. 1 and 2  are also referenced in the discussion below. In particular,  FIG. 3  is a cross-sectional view of the c-seal  230  positioned in the recess  232  between the cylinder head  180  and compressor liner  120 . The c-seal  230  has a first side (or interior/open side)  302  that faces the fourth cylinder  160  and a second side (or exterior/closed side)  304  that faces the vent port  240 . 
     The pressure (P 4 ) on the first side  302  of the c-seal  230  is the pressure in the fourth cylinder  160 , and the pressure (P V ) on the second side  304  corresponds to the pressure in the vent port  240 . Since the vent port  240  is fluidly coupled to the inlet  164  of the fourth cylinder  160 , the pressure (P V ) on the second side  304  of the c-seal  230  is the same as the pressure of the air after the third stage  284  of the compressor  100 . As such, using the exemplary pressures listed above, the pressure (P V ) on the second side  304  of the c-seal  230  is typically about 1800 psig. 
     As noted above, when the fourth piston  162  is in a first or withdrawn position (e.g., as shown in  FIGS. 1 and 2 ), the air in the fourth cylinder  160  is at the same pressure (P 4 ) as the air in the third cylinder  150 . As such, in this condition, the pressure (P 4 ) on the first side  302  of the c-seal  230  is approximately equally to the pressure (P v ) on the second side  304  of the c-seal  230 , thereby resulting in a pressure drop or differential (ΔP) of zero. When the fourth piston  162  is in a second or pressurizing position (e.g., moved to the left of the position shown in  FIGS. 1 and 2 ), the air in the fourth cylinder  160  is compressed to the final pressure of the fourth stage  286 . Using the exemplary pressures discussed above, the pressure (P 4 ) on the first side  302  of the c-seal  230  rises to about 5000 psig. The pressure (P v ) on the second side  304  of the c-seal  230  is unchanged. As a result, the pressure drop or differential (ΔP) between the pressure (P 4 ) on the first side  302  of the c-seal  230  and the pressure (P v ) on the second side  304  of the c-seal  230  in one exemplary embodiment is about 3200 psig. 
     Typically, the c-seal  230  is designed to withstand pressures of at least 3200 psig such that the c-seal  230  better accommodates the pressure changes over a long service life. In contrast, if the vent port extended to ambient, e.g., a pressure of zero, the pressure differential (ΔP) would be about 5000 psig. Such a pressure differential (ΔP) may cause undesirable issues for the c-seal, particularly when the compressor operates at speeds such as 5000 RPM or higher and at temperatures of about 400° F. or greater. However, the pressure differentials between the third and fourth stages resulting from the vent port  240  and vent tube  250  are suitable for the c-seal  230 . 
     This arrangement provides a number of advantages. The vent port  240  and vent tube  250  to the inlet of the fourth stage  286  enables an improved service life for the c-seal  230 . For example, the vent port  240  and vent tube  250  may prevent the c-seal  230  from being loaded in an opposite direction from which is it is designed. Moreover, due to the improved performance of the sealing assembly  200 , the compressor  100  operates to recharge the ARS with a reduced number of cycles. Additionally, since the leaked air is returned to the third stage pressure, the efficiency of the compressor  100  is improved since, in effect, the work of the first three stages is not lost. 
     Accordingly, compressors with improved sealing assemblies are provided. Such a compressor may form part of an ARS with long lasting service life at high speeds (e.g., greater than 5000 RPM), high pressures (e.g., greater than 5,000 psig), and high temperatures (e.g., greater than 400° F.). The exemplary embodiments may be useful in the general context of any two or more seal surfaces, for example, in pressurized vessels to prevent the escape of pressure or in systems containing two or more separate mediums to prevent them from mixing together. In addition to the depicted embodiments, exemplary embodiments may also be well suited for use in high pressure hydraulic equipment; high performance pneumatic, vacuum and compressor systems; and high pressure systems in general where stationary, oscillatory, rotary or reciprocating surfaces may be sealed. 
     In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Numerical ordinals such as “first,” “second,” “third,” etc. simply denote different singles of a plurality and do not imply any order or sequence unless specifically defined by the claim language. The sequence of the text in any of the claims does not imply that process steps must be performed in a temporal or logical order according to such sequence unless it is specifically defined by the language of the claim. The process steps may be interchanged in any order without departing from the scope of the invention as long as such an interchange does not contradict the claim language and is not logically nonsensical. 
     Furthermore, depending on the context, words such as “connect” or “coupled to” used in describing a relationship between different elements do not imply that a direct physical connection must be made between these elements. For example, two elements may be connected to each other physically, electronically, logically, or in any other manner, through one or more additional elements. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.