Patent Application
20050239558
The present invention relates generally to rotary power transmission devices, and more particularly to an arrangement for transmitting torque between a male shaft and a female or hollow shaft, such as a hub or quill shaft.
Many applications exist in industrial and commercial settings for transmitting rotary power between a driving machine and a driven machine. Power is generally transmitted from a driving shaft on the driving machine to a driven shaft on the driven machine.
In rotating machinery of the type mentioned above, various arrangements are known and are presently in use for coupling the driving and driven shafts. In certain arrangements, a male driving shaft (extending from a motor, a gear reducer, or some other type of equipment) and a male driven shaft are coupled through a coupling arrangement which is interposed between the shafts. In other arrangements, a hub or female or hollow member receives the male driving shaft, typically with the male shaft extending from the driving equipment and a female or hollow hub, on the driven machine being adapted to mate with the male driving shaft. In still other arrangements, a female shaft, commonly referred to as a “quill shaft” may extend from the driven load and present an aperture in which a male driving shaft is inserted for driving the quill or hollow end shaft. In certain devices, the quill shaft may be supported at a single end or both ends within the driven device.
For example, in certain worm drive gear reducers, the quill shaft may be supported at an extremity thereof opposite a drive shaft, with driving shaft bearings serving to support both the driving shaft and the quill shaft at the input end of the quill shaft. In other arrangements, an additional bearing may be supplied at the quill shaft input end. In yet another arrangement the driving shaft in the driving machine may be a hollow shaft or quill. The driven shaft in this case would be male and would be configured to extend into the female or hollow driving shaft.
Depending upon the alignment of the driving shaft and the mating driven shaft angular displacement of the male shaft with respect to the female shaft may occur during each rotational cycle. That is, unless exactly aligned coaxially, the shafts will undergo some relative movement in rotation due to slight misalignment. This is particularly problematic in the case of hollow shafts and similar arrangements, where substantial wear, and fretting may take place at the interface between the male shaft and the internal surface of the hollow shaft. Over time, if such fretting is allowed to continue, degradation of one or both shafts may occur, or the shafts may even undergo welding in which the shafts ultimately are fused to one another and cannot be separated. Such wear, fretting, and welding degrades the operation of one or both devices, and ultimately results in maintenance cost, primarily in replacement of parts or the entire machines themselves, as well as downtime and labor costs.
Attempts have been made to ameliorate the interface between male shafts and female or hollow members, such as quill shafts. For example, in certain environments, inserts, such as plastic sleeves, may be provided between hollow shafts and male shafts to absorb wear or at least to absorb the movement of misalignment. However, the presence of such sleeves implies that the desired torque available from the driving machine cannot be provided to the driven machine without either enlarging one or both shafts. Typically, the arrangement must be oversized or down rated to accommodate the smaller male shaft that is inserted into the intermediary sleeve, or the hollow shaft enlarged to the size required to accommodate the internally-fitting sleeve. Greases and lubricants have also been used in the interface between the male shafts and hollow shafts. However, such temporary measures have been found inadequate, and eventually are worn or eliminated from the interface, permitting fretting, wear and eventual welding of the interface.
There is a need, therefore, for an improved technique for mating male shafts and hollow shafts, such as quill shafts.
The present invention provides a novel approach to coupling male shafts and hollow members, such as quill shafts, designed to respond to such needs. The technique makes use of a direct connection between the male shaft and the hollow member, with driving between the shafts being accomplished by any suitable torque-transmitting feature. Such features might include keys, splines, and so forth. A layer of conforming material is disposed between the male shaft and the interior surface of the hollow member. The conforming material may be inserted in a liquid form or a semi-liquid form. The material is then cured or bonded to establish a barrier between the male shaft and the interior surface of the hollow member. This self-forming sleeve allows the mating male and hollow shafts to be disassembled, after extensive periods of operation, without excessive force and without significant damage to shafts and connected machinery.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Turning now to the drawings, and referring first to
The driven machine, in the embodiment illustrated in the figures, is a 90 degree gear reducer 20 in a form of a worm-drive reducer. The hollow bore 12 is provided with a keyway 22 designed to interface with the key 18 of the shaft 10 when the male shaft is inserted into the hollow bore. An input interface is provided on the gear reducer 20 to receive the driving electric motor 14. In the illustrated embodiment, the input interface 24 presents a peripheral flange 26 designed to receive and support the motor, and to maintain the motor in general alignment so as to support the male shaft 10 within the hollow bore 12 in a generally coaxial alignment. The flange is supported on a housing 28 within which internal components provide for gear reduction and drive an output shaft 30 which extends from the housing.
It should be noted that the particular application illustrated in the figures is provided for exemplary purposes only. In general, the present techniques allow for installing a self-forming sleeve at an interface between a male shaft and a hollow member, such as a bore. However, while a key-drive is illustrated in the figures, other types of torque-transmitting members may be employed, including multiple keys, splines, straight shafts set within a hub via set screws or other torque transmitting elements, and so forth. Similarly, the hollow bore 12 in the gear reducer illustrated in the figures may present conforming features to mate with those of the male shaft. Other types of mounting arrangements than those shown in the figures may, of course, be provided for the mated members. Indeed, in certain applications, the components may not be directly coupled as shown in the figures, but may be linked by intermediate components, such as mounting adapters, mounting feet, couplings, and so forth. Finally, while the application in a gear reducer, and more particularly to a hollow (quill) shaft, as discussed in greater detail below, is a particularly well-suited application, the present technique may find significant utility and other environments and applications. These applications may or may not involve speed or torque reduction or entries.
In the embodiment of the gear reducer illustrated in
As will be appreciated by those skilled in the art, substantial wear and fretting may take place at an interface between the bore 12 of the quill shaft and the male shaft 10 illustrated in
In accordance with the preferred embodiment of the present technique, the self-forming sleeve 54 comprises a low strength adhesive barrier that remains flexible during operation of the machine. That is, the barrier is preferably of a low stiffness, but is not fluid following application and installation. One exemplary material that has been found to provide good results is commercially available from Loctite Industrial Adhesives, a division of Henkel Technologies, under the designation PST 567, which is generally used as a thread sealing compound. This product is a paste-like anaerobic compound stays relatively liquid or semi-liquid with exposure to oxygen, but will cure once placed into the interstice between the rotating members in the present technique. The compound employed in current embodiments has an approximately 24 hour cure time, after which it essentially loses its fluid properties and becomes a semi-permanent sleeve between the components. That is, the component can be disassembled, but the self-forming sleeve will not leak or be extruded from the interface during normal operation. Other suitable materials are believed to include two-part epoxies, such as epoxies available for repairing polyvinylchloride components.
It should be noted that as used herein, the terms “curing” and “curable” are not intended to connote any particular type of chemical or material process, but should be broadly understood to mean a change in physical properties by which the material will resist flowing from or being eliminated from the location between the shaft and bore in which the self-forming sleeve is installed. A number of materials, with various physical property-changing processes may be appropriate for use as the self-forming sleeve. These might include various adhesives and sealants. Compounds that change viscoelastic properties, compounds that solidify or “set up”, bond, link, cross link, or from which solvents leach or evaporate to provide the desired plastic properties needed to conform to the interstice between the shaft and bore, and yet remain sufficiently elastic during operation to work effectively as a protective sleeve.
In the present embodiment, the press or slip fit between the male shaft and the quill bore provides an approximately 0.0005-0.0015 inch clearance. This clearance, then defines the approximate thickness of the self-forming sleeve. Other fits and clearances may, of course, be used, depending upon such factors as the rotational speed of the equipment, the radius of the rotational members at the interface, the degree of misalignment anticipated, and the material provided for the self-forming sleeve. In experimental applications, the foregoing arrangement was employed to drive a quill shaft-driven gear reducer by a single-phase motor. While previous techniques employing lubricants may have generated vibration and wear-originating noise after mere minutes of operation, the present technique was found to operate quietly after 1500 hours of continuous operation, indicating significantly less contact and wear at the interface.
At step 62 the male shaft and hollow bore are assembled by the press or slip fit described above. In a typical application, the assembly may be accompanied by assembly of other components, such as securing a motor to a mounting adapter in the embodiment described above. The interface layer is then allowed to cure and bond as indicated at step 64. In certain present embodiments, the material employed does not form a strong bond to the metal of either the male shaft or the hollow bore, but forms a flexible interface therebetween. Following the curing and bonding step 64, the machine may be placed in operation and torque applied to the driven machine through the intermediary of the self-forming sleeve while avoiding wear and degradation of either the male shaft or the hollow bore due to any misalignment at the interface.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
