Patent Application
20210381522
The field of the disclosure relates generally to a driveshaft assembly for a compressor, and more particularly, to a driveshaft assembly including a thrust disk and an impeller for use in a compressor.
Recent CFC-free commercial refrigerant compositions, such as R134A, are characterized as having lower density compared to previously-used CFC or HCFC refrigerants such as R12. Consequently, an air conditioning system must process a higher volume of a CFC-free refrigerant composition relative to CFC or HCFC refrigerant to provide a comparable amount of cooling capacity. To process higher volumes of refrigerant, the design of a gas compressor may be modified to process refrigerant at higher operating speeds and/or operate with higher efficiency.
Centrifugal compressors that make use of continuous dynamic compression offer at least several advantages over other compressor designs, such as reciprocating, rotary, scroll, and screw compressors that make use of positive displacement compression. Centrifugal compressors have numerous advantages over at least some positive displacement compressor designs, including lower vibration, higher efficiency, more compact structure and associated lower weight, and higher reliability and lower maintenance costs due to a smaller number of components vulnerable to wear. High-capacity cooling systems employing centrifugal compressors operate a driveshaft at high-rotational speeds to transmit power from the motor to the impeller to impart kinetic energy to the incoming refrigerant. To mitigate the challenges associated with the high-rotational speed driveshafts, centrifugal compressors typically require relatively tight tolerances and high manufacturing accuracy. Additionally, other types of mechanical systems, such as motors, pumps, and turbines etc., also operate driveshafts at high-rotational speeds. As known to those familiar with these types of rotating mechanical systems, loosening and misalignment of components mounted to the driveshaft may occur during operation creating unbalanced loads which result in vibrations, subjecting the driveshaft to cyclic stress loadings, resulting in decreased operational lifespans and premature failures, particularly premature failure of bearings and seals.
Centrifugal compressors include one or more bearing assemblies which support and maintain alignment of the driveshaft. In typical centrifugal compressors, components, such as the impeller and the thrust disk, are separately coupled to the driveshaft using friction fit connections, e.g., such as a press fit or a shrink fit. The driveshaft, impeller, and the thrust disk, rotating at high-rotational speeds, induce centrifugal forces which increase with increased rotational speed. The centrifugal force is directed radially, away from the axis of rotation, pulling the components outward away from the driveshaft, loosening the friction fit connections. Furthermore, the inertia of the components, particularly radial distribution of mass extending away from the axis of rotation contributes to the centrifugal force further loosening the friction connections with the driveshaft. The loosening of connections creates eccentric loads such that the center of mass of the mounted component is not coincident with the axis of rotation of the driveshaft. The effects of eccentric loading are further exaggerated at high-rotational speeds resulting in vibrations that increase wear and may result in increased system downtime.
The design of mounted components on the high-rotational speed driveshaft pose an on-going challenge of maintaining the friction fit connections between the driveshaft and the components. Furthermore, maintaining alignment of the center of gravity of the components coincident with the axis of rotation of the driveshaft during high-rotational operating speeds facilitates avoiding eccentric loads that lead to vibrations which may damage components of the centrifugal compressor.
This background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In one aspect, a compressor system includes a compressor housing and a driveshaft rotatably supported within the compressor housing. The compressor system further includes an impeller that imparts kinetic energy to incoming refrigerant gas upon rotation of the driveshaft, a thrust disk coupled to the driveshaft, and a bearing assembly mounted to the compressor housing. The impeller includes an impeller bore having an inner surface, and the thrust disk includes an outer disk and a hub. The bearing assembly rotatably supports the outer disk of the thrust disk. The hub is disposed within the impeller bore, and includes a hub outer surface in contact with the inner surface of the impeller bore. A first contact force between the hub outer surface and the inner surface of the impeller bore increases with increased rotational speed of the driveshaft.
In another aspect, a driveshaft assembly for a compressor includes a driveshaft, a thrust disk coupled to the driveshaft, and an impeller coupled to the thrust disk. The thrust disk includes an outer disk and hub, which includes a hub outer surface. The impeller includes an impeller bore having an inner surface. The hub of the thrust disk is disposed within the impeller bore, and the hub outer surface is in contact with the inner surface of the impeller bore. A first contact force between the hub outer surface and the inner surface of the impeller bore increases with increased rotational speed of the driveshaft.
In yet another aspect, a method of assembling a compressor includes coupling a thrust disk to a driveshaft by inserting the driveshaft into a thrust disk bore of the thrust disk. The method further includes coupling an impeller to the thrust disk by inserting a hub of the thrust disk into an impeller bore of the impeller such that an outer surface of the hub is in contact with an inner surface of the impeller bore and a first contact force between the hub outer surface and the inner surface of the impeller bore increases with increased rotational speed of the driveshaft. The method further includes mounting bearings to a compressor housing such that the bearings rotatably support an outer disk of the thrust disk.
Various refinements exist of the features noted in relation to the above-mentioned aspects. Further features may also be incorporated in the above-mentioned aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments may be incorporated into any of the above-described aspects, alone or in any combination.
The following figures illustrate various aspects of the disclosure.
Corresponding reference characters indicate corresponding parts throughout the drawings.
Referring to
Referring to
The first stage impeller 106 and second stage impeller 116 are connected at opposite ends of a driveshaft 104 that rotates about a driveshaft axis A104. The driveshaft extends from a driveshaft first end 130 to a driveshaft second end 132, and is axisymmetric about the driveshaft axis A104. Additionally, the driveshaft axis A104 extends through a center of gravity of the driveshaft 104. The driveshaft 104 is operatively connected to a motor 108 positioned between the first stage impeller 106 and second stage impeller 116, such that the motor 108 rotates the driveshaft 104 about the driveshaft axis A104. The first stage impeller 106 and the second stage impeller 116 are both coupled to the driveshaft 104 such that the first stage impeller 106 and second stage impeller 116 are rotated at a rotation speed selected to compress the refrigerant to a pre-selected pressure exiting the second refrigerant exit 120. Any suitable motor may be incorporated into the compressor 100 including, but not limited to, an electrical motor.
In reference to
In reference to
Referring to
The thrust disk 204 is coupled to the driveshaft 104 by a friction or press fit connection. For example, the thrust disk bore surface 208 is in frictional engagement with the second shaft portion outer surface 146 and the outer disk 210 is in frictional engagement with the first end surface 138 of the driveshaft 104 such that rotation of the driveshaft 104 imparts rotation to the thrust disk 204. The thrust disk bore surface 208 is in contact with the second shaft portion outer surface 146 with limited or no gaps or spaces. Additionally, the radius R206 is sized such that there is interference between the thrust disk 204 and the driveshaft 104. In example embodiments, components, such as the thrust disk 204 are coupled to the driveshaft 104, using a press fit, also referred to as interference fit and/or a friction fit. Friction between mating surfaces of the two parts is generated after the two parts having interference are press fit assembled. Based on the amount of interference between thrust disk 204 and the driveshaft 104, the thrust disk 204 may be assembled onto the driveshaft 104 using a hammer or hydraulic ram. In some cases, the components may be assembled using shrink fitting techniques. Shrink fitting techniques are performed by selective heating and/or cooling of the components to be coupled by a shrink fit. In some embodiments, for example, the thrust disk 204 is heated, causing expansion of the thrust disk bore 206 such that the second shaft portion 136 may be inserted and positioned within the expanded thrust disk bore 206. Subsequently, the thrust disk bore 206 shrinks upon cooling of the thrust disk 204 and contracts around the second shaft portion 136. In some embodiments, one or more alignment features or components may be used to assemble mating components, including for example and without limitation, an alignment pin, keyed features, or other features that are engaged between the thrust disk and the driveshaft.
The driveshaft 104, the first stage impeller 106, and the thrust disk 204 are part of a driveshaft assembly 201 of the compressor 100. In the illustrated embodiment, the driveshaft assembly 201 also includes the second stage impeller 116. The driveshaft assembly 201 may include additional or fewer components in other embodiments. In some embodiments, for example, the second stage impeller 116 may be coupled to the second end 132 of the driveshaft 104 by a thrust disk in the same manner as the first stage impeller 106.
In reference again to
The hub radius R216 is less than the disk radius R210. In the illustrated embodiment, for example, the disk radius R210 is about 2-3 times greater than the hub radius R216. In other embodiments, the disk radius R210 may be greater than or less than 2-3 times greater than the hub radius R216. Additionally, the mass of the outer disk 210 is greater than the mass of the hub 216. The centrifugal force is proportional to the mass and the radial distribution of mass. Accordingly, the centrifugal force generated on the outer disk 210 is greater than a centrifugal force generated on the hub 216 during high-speed rotation of driveshaft 104. In some embodiments, the centrifugal force on the outer disk 210 is much greater than the centrifugal force on the hub 216.
The radius R206 of the thrust disk bore 206 is less than the first radius R134 (
In reference to
The first impeller bore 306 includes an impeller inner surface 310 that defines the boundary of the first impeller bore 306. The hub 216 of the thrust disk 204 is disposed within the first impeller bore 306 of the impeller 106, such that the impeller axis A106 is coincident with both the thrust disk axis A204 and the driveshaft axis A104. The hub 216 is press fit within the first impeller bore 306 such that the outer surface 220 is frictionally connected with the impeller inner surface 310 with minimal gaps or spaces. In some example embodiments, the hub 216 may be frictionally connected with the first impeller bore 306 using shrink fitting techniques. Accordingly, rotation of the driveshaft 104 results in rotation of the thrust disk 204 and the impeller 106. The thrust disk 204 transmits torque from the driveshaft 104 to the impeller 106 and, as such, the impeller 106 is not directly mounted to the driveshaft 104. The thrust disk 204 and the impeller 106 are arranged relative to the driveshaft 104 such that the center of gravity of the thrust disk 204 and the impeller 106 are aligned with the driveshaft axis A104. In other words, the driveshaft axis A104, thrust disk axis A204, and the impeller axis A106 are all co-axial. Furthermore, the assembly of the driveshaft 104, the thrust disk 204, and the impeller 106 is axisymmetric about the driveshaft axis A104.
Referring again to
The inner radius of the second hub portion 216b may be smaller than the inner radius of the first hub portion 216a, such that the second inner surface 208b has greater interference (i.e., a tighter fit) with the driveshaft 104 compared with the interference between the first inner surface 208a and the driveshaft 104. In some embodiments, there may be a clearance or gap C1 between the first inner surface 208a and the driveshaft 104. For example, the clearance C1 between the first inner surface 208a and the driveshaft 104 may be between 0.1 and 1 (mm).
Rotation of the driveshaft 104, the thrust disk 204, and the impeller 106 induce centrifugal forces directed in an outward radial direction, perpendicular to the driveshaft axis A104. The induced centrifugal forces increase with increased rotational speed squared. The centrifugal force is an inertial force that is proportional to the radial distribution of mass about the axis of rotation, i.e., the driveshaft axis A104. The outer disk 210 has a larger radius R210 compared with the hub radius R216 of the hub 216. Accordingly, the outer disk 210 experiences a greater centrifugal force compared to the centrifugal force experienced by the hub 216. The centrifugal force on the outer disk 210 pulls the outer disk 210 in a radial direction, perpendicular to the driveshaft axis A104, away from the driveshaft 104. The centrifugal force on the outer disk 210 also exerts an outward radial force on the first hub portion 216a which is proximate to the outer disk 210. The outward radial force exerted on the first hub portion 216a, causes the first outer surface 220a of the first hub portion 216a to exert a force against the impeller inner surface 310, referred to as a first contact force F1, thereby increasing the frictional connection between the first outer surface 220a and the impeller inner surface 310. The first contact force F1 increases with increased rotational speed of the driveshaft 104, and provides sufficient contact force to maintain the friction connection between the hub 216 and the impeller 106 and to maintain the alignment of the center of gravity of the impeller 106 and the center of gravity of the thrust disk 204 at high-rotational operation speeds.
The centrifugal force on the second hub portion 216b pulls the second hub portion 216b radially outward away from the driveshaft 104. The centrifugal force on the outer disk 210 and the first hub portion 216a may cause the second hub portion 216b to flex, slightly, in a radially inward direction, towards the driveshaft 104. In some embodiments, the friction fit between the second hub portion 216b and the driveshaft 104 may decrease with increased rotational speed of the driveshaft 104. The contact force F2 between the second inner surface 208b of the second hub portion 216b and the driveshaft 104 is sufficient to maintain the friction connection between the thrust disk 204 and the driveshaft 104 and the alignment of the center of gravity of thrust disk 204 with the driveshaft axis A104 at normal operational speeds of the driveshaft 104. In other words, as the rotational speed of the driveshaft 104 increases, the interference fit or connection between the thrust disk 204 and the driveshaft 104 may decrease slightly and the connection between the thrust disk 204 and the impeller 106 becomes stronger (i.e., tighter). The friction fit or connection between the thrust disk 204 and the driveshaft 104 prevents slipping or relative movement between the thrust disk 204 and the driveshaft 104, and. enables the transfer of torque from the driveshaft 104 to the thrust disk 204 and, consequently, from the driveshaft 104 to the impeller 106.
The impeller 106 further includes a screw 314 that extends through the second impeller bore 308 and the first impeller bore 306, and into the blind bore 142 of the driveshaft 104. The screw 314 includes a threaded portion having threads that are engaged with threads defined on the bore inner surface 144 (not shown). The screw 314 includes a head 316 that is engaged with the impeller second end 304. When the screw 314 is tightened, the screw 314 compresses the impeller 106 against the thrust disk 204, thereby facilitating transmission of torque from the thrust disk 204 to the impeller 106. More specifically, the screw 314 forces the impeller first end 302 into contact with the second disk surface 214 of the thrust disk 204 thereby causing a portion of the outer disk 210 to be compressed between the impeller first end 302 and the first end surface 138 of the driveshaft 104. Tightening of the screw 314 generates a clamping force on the thrust disk 204. The threads of the screw 314 are arranged such that rotation of the driveshaft 104 does not loosen or unscrew the threads of the screw 314 with the threads of the blind bore 142.
Accordingly, in the embodiments illustrated in this disclosure, the thrust disk 204, the impeller 106, and the driveshaft 104 are arranged such that the frictional connections or fits between the components are generally maintained at operational rotational speeds of the driveshaft 104. The frictional fit between the driveshaft 104 and the thrust disk 204 may decrease slightly with increased rotational speed of the driveshaft 104. The decrease in friction fit between the driveshaft 104 and the thrust disk 204 is not highly dependent on the rotational speed of the driveshaft 104. Further, increases in the rotational speed of the driveshaft 104 may increase the frictional connection between the thrust disk 204 and the impeller 106. More specifically, increases in the rotational speed of the driveshaft 104 increases the first contact force F1 between the hub 216 and the impeller 106 and only slightly decreases the second contact force F2 between the hub 216 and the driveshaft 104. The first and second contact forces F1, F2 are sufficient to maintain frictional connection between the assembled components. Furthermore, the assembly of the components is such that the center of gravity of the thrust disk 204 and the impeller 106 are coincident with the axis of rotation, limiting eccentric loading at high-rotational speeds.
Embodiments of the systems and methods described achieve superior results as compared to prior systems and methods associated with thrust bearing assemblies. The thrust disk, impeller, and driveshaft assembly facilitate maintaining alignment of the rotating components at high-rotational operating speeds consistent with compressor systems. The high-rotational operating speeds of the driveshaft increase friction fit connections between the thrust disk and the impeller, and maintain the friction fit connection between the thrust disk and the driveshaft. In some embodiments, the impeller is not directly coupled to the driveshaft, and torque is transmitted from the driveshaft to the impeller through the thrust disk. The improved friction fit connection maintains the alignment between the center of gravity of the thrust disk, the impeller, and the driveshaft with the axis of rotation. The disclosed assemblies are compatible with centrifugal compressors, which typically operate at high rotational speeds. The assembly of the components described herein may be incorporated into the design of any type of centrifugal compressors. Non-limiting examples of centrifugal compressors suitable for use with the disclosed system include single-stage, two-stage, and multi-stage centrifugal compressors. Additionally, the described assembly is well suited for other applications including other mechanical systems having components, such as an impeller and bearing assemblies coupled to a high-rotational speed driveshaft.
Unlike known bearing systems and impellers mounted to a driveshaft of compressor systems, the thrust disk, impeller, and driveshaft assembly described in this disclosure enables the alignment of the center of gravities of the components as well as maintaining of friction fit connections, regardless of the high-rotational operation speed of the driveshaft, both of which are important factors in the successful implementation of centrifugal compressors as discussed above. Furthermore, the high-rotational speeds serve to improve the friction fit between the thrust disk and the impeller, maintaining friction connections and preventing eccentric loads on the driveshaft. The described assembly may result in improved operational lifespan while reducing wear of components thereby lowering costs associated with repair and downtime of rotational machines. The assembly described provides enhanced features increasing the working life and durability of impeller, thrust disk, and driveshaft for use in the challenging operating environment of refrigerant compressors of HVAC systems.
Example embodiments of compressor systems and methods, such as refrigerant compressors, are described above in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, components of the system and methods may be used independently and separately from other components described herein. For example, the impeller and thrust disk described herein may be used in compressors other than refrigerant compressors, such as turbocharger compressors and the like.
When introducing elements of the present disclosure or the embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” “containing” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., “top”, “bottom”, “side”, etc.) is for convenience of description and does not require any particular orientation of the item described.
As various changes could be made in the above constructions and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawing(s) shall be interpreted as illustrative and not in a limiting sense.
