Patent Application
20060078438
The present invention generally relates to compressor assemblies, and, more particularly, to a compressor assembly having counter rotating motor and compressor shafts.
Traditional positive displacement (reciprocating piston) compressor assemblies include a compressor coupled to a motor using belt drive or direct drive mechanisms which transfer power from the motor to the compressor for reciprocating the piston (or pistons) of the compressor. Conventionally, in such belt drive and direct drive configurations, the drive shaft of the motor (herein after referred to as the motor shaft) and the crank shaft of the compressor (hereinafter referred to as the compressor shaft) turn in the same direction to simplify the drive train of the compressor assembly.
A significant problem with reciprocating piston compressors is that the torque of the compressor shaft varies significantly during rotation of the shaft (i.e., reciprocation of the piston) causing excessive torsional vibration of the compressor assembly. In the past, three common methods have been used for reducing such torsional vibration. The first of these methods was to divide the compressor displacement into several smaller piston/cylinder assemblies. The second method was to increase the size and moment of inertia of the compressor flywheel. These solutions add cost and size to the compressor and have practical upper limits. The third method involved increasing compressor speed. However, this solution also generates excessive noise and increases reciprocating imbalance. Moreover, the effectiveness of all three solutions is limited to reduction rather than elimination of torsional vibration and requires compromise between the types of imbalance and noise reduction.
Consequently, it is desirable to provide a compressor assembly having a reciprocating piston compressor driven by a motor, wherein torsional vibration in the compressor assembly is greatly reduced or eliminated.
Accordingly, the present invention is directed to a compressor assembly suitable for use in a compressor such as an air compressor, or the like, having counter rotating motor and compressor shafts with mass moments of inertia balanced to substantially eliminate torsional vibration.
In exemplary embodiments, the compressor assembly includes a compressor coupled to a motor (e.g., an electric motor, an engine, or the like) via a belt drive. The belt drive provides a speed reduction between the motor and compressor and causes the compressor shaft to rotate in the direction opposite that of the motor shaft. The relative values of the mass moments of inertia about the axes of rotation of the rotating motor and compressor shafts are engineered to be generally inversely proportional to the relative shaft speeds. In this manner, the mass moments of inertia may be balanced to substantially eliminate torsional vibration.
It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.
The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which:
Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
Referring generally
The belt drive 106 includes a flywheel 120 mounted to the compressor shaft 122, a motor sprocket 124 mounted to the motor shaft 126, and a belt idler or idler bearing 128 mounted to the compressor housing 108. The flywheel 120 and belt idler 128 receive the belt 130, which passes over the motor sprocket 124. In the exemplary embodiment illustrated, the belt 130 comprises a flat belt formed of a material such as rubber, or the like, which may have a central cord of a material such as nylon for added strength. However, it will be appreciated by those of ordinary skill in the art, that the belt 130 may alternatively comprise other types of belts (e.g., a poly V belt, a timing belt, etc.), chains (e.g., a bicycle chain), or the like, without departing from the scope and intent of the present invention.
The piston 112 includes a connecting rod 132 journaled to the compressor shaft 122, which in turn mounts the flywheel 120. The belt 130 passes over and is driven by the motor sprocket 124, which is coupled to the spinning motor shaft 126. The belt 130 rotates the flywheel 120 turning the compressor shaft 122 for reciprocating the piston 112. The belt idler 128 is used for tensioning the belt 130 and for routing the belt 130 over the motor sprocket 124 to provide counter or reverse rotation between the flywheel 120 and compressor shaft 122, and the motor sprocket 126 and motor shaft 126. The belt idler 128 rotates or turns in the same direction as the compressor shaft 122 and flywheel 120 (e.g., counterclockwise), and in a direction opposite the direction that the motor shaft 126 and motor sprocket 124 rotate or turn (e.g., clockwise).
In accordance with the present invention, the belt drive 106 provides a speed reduction between the motor 104 and the compressor 102 (i.e., provides a reduction in rotational speed between the motor shaft 126 and the compressor shaft 122) and causes the compressor shaft 122 to rotate in a direction opposite the direction of rotation of the motor shaft 126. Preferably, the relative values of the mass moments of inertia about the axes of rotation of the rotating motor and compressor shafts 122 & 126 are calculated to be at least approximately inversely proportional to the relative shaft speeds of the shafts. Since the belt idler 128 rotates in the same direction as the compressor shaft 122 and flywheel 120, the belt idler inertia product is added to the inertia product of the compressor rotating components. The mass moment of inertias and shaft rotational speeds (RPM) of the motor shaft 126 and the compressor shaft 122 are thus related by the expression:
Ic+Ii·Ni/Nc=Im·Nm/Nc
where Ic is the mass moment of inertia of the compressor shaft 122 including the mass moment of inertias for all rotating compressor shaft components (e.g., compressor shaft 122, flywheel 120, and the like), Nc is the shaft rotational speed of the compressor shaft 122, Ii is the mass moment of inertia of the belt idler 128 including the mass moment of inertias for all rotating belt idler components (e.g., shaft 134, idler sprocket 136, and the like), Ni is the shaft rotational speed of the belt idler 128, Im is the mass moment of inertia of the motor shaft 126 including the mass moment of inertias for all rotating motor shaft components (e.g., motor shaft 126, motor sprocket 124, fan 138, and the like), and Nm is the shaft rotational speed of the motor shaft 126. For example, in one specific embodiment, if the speed of compressor shaft 122 is one half of the speed of the motor shaft 126, the mass moment of inertia of the rotating compressor shaft 122 (including the mass moment of inertia of the belt idler 128) is calculated to be at least approximately twice that of the rotating motor shaft 126. In this manner, the mass moments of inertia may be balanced to eliminate or at least substantially eliminate torsional vibration in compressor assembly 100.
It is believed that the present invention and many of its attendant advantages will be understood by the forgoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.
The present application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 60/382,123 filed May 21, 2002. Said U.S. Provisional Patent Application Ser. No. 60/382,123 is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60382123 | May 2002 | US |
