Patent Application
20130061704
The presently described subject matter generally relates to an enveloping gear arrangement and, more particularly, to an enveloping gear arrangement that uses a spiroid gear arrangement.
Gears are one of the fundamental mechanical machines and have been in use for centuries. Gears are used to, among other things, transmit power from one device to another and change the direction of force. Many types of gears are known, such as straight gears, angle gears, bevel gears, worm gears, combinations of these gears, and others. Also known are SPIROID® brand gears that use a curved gear tooth. Such a configuration of gears permits larger loads to be transferred due to the increased surface area of gear tooth relative to a straight gear formed on a similar blank.
Certain applications require gears that withstand high loads (e.g., forces). Generally, the ability to withstand such forces is accomplished by using larger gears to increase the area on the gear teeth over which the forces are exerted. The ability to withstand forces is balanced against size requirements, or conversely size limitations, of the gear assembly. While the spiroid gear accomplishes this, at times, even smaller size limitations may apply. One such gear tooth form is disclosed in Saari, U.S. Pat. No. 3,631,736 (the “'736 application”), commonly assigned with the present application and incorporated herein by reference.
Additionally, some gear assemblies are formed from multiple parts or sections. For example, a first part or section having a first set of gear teeth may be formed and a second part or section having a second set of gear teeth may be separately formed. The two parts or sections may then be coupled together using welding, adhesives, fasteners, and the like. The combined parts or sections may then mate with another geared body, such as a pinion, to translate rotation of the other geared body (e.g., the pinion) into rotation of the combined parts or sections. Due to the coupling of the separately formed parts or sections, however, the torques that may be transferred from the other geared body and the combined parts or sections may be limited.
Accordingly, there is a need for a gear system that can withstand high loads/forces in a limited or small size application.
In one embodiment, a hybrid spiroid and worm gear is formed as a gear body having an axis of rotation. The gear body has a plurality of spiroid gear teeth formed in a surface of the body, formed generally radially relative to the axis of rotation and a plurality of worm gear teeth formed in the body separate and apart from the spiroid teeth. The worm gear teeth are formed generally longitudinally relative to the axis of rotation of the gear. Alternatively, the gear body may not include the worm gear teeth.
It has been found that at least one embodiment of the hybrid spiroid gear disclosed herein provides a significant increase in torque capability for gearing without increasing the size of the gears.
In one embodiment that includes the worm gear, the gear body is formed having a pair of substantially opposing surfaces in which the spiroid gear teeth are formed a central hub, with the worm gear teeth formed between the opposing surfaces in the hub. The gear can be formed with a gap between the spiroid gear teeth and the worm gear teeth.
The gear body can be formed as two parts joined to one another at the hub in one aspect of the inventive subject matter disclosed herein. The two parts can be substantially identical to one another. The parts can be joined by press-fitting, welding, adhesive, fasteners or the like. Alternatively, the gear body may be formed as a single piece body. Such a gear body may not include separately formed parts that are joined together, such as by press-fitting the two parts together, welding the two parts together, adhering the two parts together using adhesives, fastening the two parts together using fasteners, or the like.
In an embodiment that includes the worm gear teeth, the teeth can be formed having a profile that is different from or the same as the profile of the spiroid gear teeth, where the profile is defined by a height and/or a pitch of the gear teeth.
In one embodiment, the gear is formed from a polymeric material, such as acetal material or the like. Alternatively, the gear may be formed from another material, such as aluminum, ductile iron, aluminum bronze, steel, high strength heat treated alloy steels, and the like. For example, the ability to form the gear as a single piece body in one embodiment (as opposed to forming the gear from multiple pieces that are joined together) can allow for the gear to be formed from materials that typically are not able to be welded together or otherwise connected and able to support relatively large forces or loads.
The hybrid spiroid gear assemblies disclosed herein (e.g., the hybrid spiroid and worm gear assembly and/or the spiroid gear assembly) can be configured to mesh with a pinion disposed at an angle that is other than normal to an axis of the gear body. The pinion can be formed with first and third spaced apart thread forms configured to mesh with the opposing surface spiroid gear teeth. In one embodiment, the pinion can include an intermediately disposed, second thread form configured to mesh with the gear worm teeth. Alternatively, the gear may not include the worm teeth and/or the pinion may not include the second thread form for meshing with gear worm teeth. The pinion first and third thread forms may be identical. The second thread form can be different from or identical to the first and third thread forms. Alternatively, the second thread form may not be included or provided in the gear body. The first, second and third thread forms can also be formed as a continuous thread form in the pinion.
One embodiment of method for making the hybrid spiroid and worm gear includes forming the first gear body part, forming the second gear body part, and joining the first and second gear body parts to form the hybrid spiroid and worm gear. The first and second body parts can be formed identical to one another.
In another embodiment, a spiroid gear assembly includes a single piece gear body having a first axis of rotation and including opposing first and second surfaces each having spiroid gear teeth formed therein. The gear teeth radially extend outward from the first axis of rotation. The gear teeth on the first surface also extend from the first surface toward the second surface and the gear teeth on the second surface also extend from the second surface toward the first surface. The gear teeth on the first surface and the gear teeth on the second surface are configured to concurrently engage teeth of a pinion such that rotation of the pinion is translated to rotation of the gear body around the first axis of rotation.
In another embodiment, a method (e.g., for forming a gear assembly) includes providing a single piece blank having a first axis of rotation. The blank includes opposing first and second surfaces. The method also includes positioning a hob between the first and second surfaces of the blank. The hob includes a second axis of rotation and cutting teeth positioned along a length of the hob. The hob is positioned such that the cutting teeth concurrently engage both of the first and second surfaces of the blank. The method further includes rotating the blank around the first axis of rotation and the hob around the second axis of rotation such that the cutting teeth of the hob concurrently cut gear teeth in each of the first and second surfaces of the blank to form a gear body of a spiroid gear assembly.
In another embodiment, a hobbing tool includes a body and one or more cutting teeth. The body is elongated along a first axis of rotation. The one or more cutting teeth encircle the body along at least a portion of a length of the body. The one or more cutting teeth also are spaced along the length of the body such that cutting teeth concurrently engage opposing first and second surfaces of a gear body blank. The body is configured to be rotated about the first axis of rotation while the gear body blank is rotated about a second axis of rotation such that the one or more cutting teeth concurrently cut gear teeth in both of the first and second surfaces of the gear body blank.
These and other features and advantages of the presently described inventive subject matter will be apparent from the following detailed description, in conjunction with the appended claims.
The benefits and advantages of the presently described inventive subject matter will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein:
While the presently described inventive subject matter is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described example embodiments of the inventive subject matter with the understanding that the present disclosure is to be considered an exemplification of the inventive subject matter and is not intended to limit the scope of the inventive subject matter to the specific illustrated embodiments.
It should be understood that the title of this section of this specification, namely, “Detailed Description,” relates to a requirement of the United States Patent Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein.
Referring now to the figures and in particular to
The opposing gear surfaces 12, 14 have teeth 16, 18 that extend from the periphery 22, partially downward toward the central hub region 20. In the illustrated gear assembly 10, the opposing surfaces 12, 14 are formed with a spiroid gear form 24 and the central hub portion 20 is formed with a worm gear form 26. A gap 27 is defined between the spiroid gear form 24 and the worm gear form 26. The spiroid gear form 24 has a curved tooth profile 28. In the illustrated embodiment, the worm gear 26 has lower gear tooth profile. It will, however, be appreciated that the tooth profile of the worm gear form 26 can be the same as the tooth profile of the spiroid gear form 24 insofar as the pitch, tooth height, and/or like tooth characteristics.
Referring to
The illustrated gear system (the gear assembly 10 and a pinion 34) has a pinion 34 that has two different and separate tooth profiles 36, 38. Two outer pinion (worm) tooth profiles 36 (e.g., arrangements of one or more teeth of the pinion) are designed to engage the larger opposing spiroid gear profiles 24, while the inner pinion (worm) tooth profile 38 is designed to engage the central worm gear tooth profile 26. It will, however, be appreciated that the pinion 34 can be configured with a single tooth (worm pinion) profile and can also be formed having a continuous tooth profile along the length of the pinion 34. Alternately, the pinion 34 can be formed tapering (with a decreasing diameter) toward the center of the pinion 34 from the ends, as indicated at P in
As shown in
Tests were conducted to compare the torque capability of the hybrid gear to that of a double spiroid gear (without the central worm gear) and a worm gear. This was conducted by measuring the torque at failure which was determined to be when the gear teeth fail under applied torque (referred to herein as the “maximum torque” or “maximum load”).
Testing was carried out using an ITW Intron device T as illustrated, in part, in
Three sets of test were conducted. The first set of tests was carried out on three worm gear samples. The calculated results of the test are shown in Table 1, below, which show the maximum load indicated for the worm gear.
The second set of tests was carried out on six double spiroid gear samples. The calculated results of the test are shown in Table 2, below, which show the maximum load indicated for the double spiroid gears.
The third set of tests was carried out on six hybrid enveloping spiroid and worm gear samples. The calculated results of the test are shown in Table 3, below, which show the maximum load indicated for the hybrid spiroid and worm gear.
In each case, the maximum load was calculated as the test device force multiplied by the disk radius (2.5 inches) and multiplied by the RPM ratio of 19. The RPM ratio is the ratio of rotational speed of the pinion to the tested gear. Thus, the maximum load is calculated as the test device force (in pounds) multiplied by 47.5 inches. All of the gears were made from the same material, Acetal 100.
With respect to the worm gear, the average (of three samples) maximum load at failure for the three tests was found to be 14.64 lbs, which corresponds to an average torque limit for the worm gear of 14.64×2.5×19=694.4 in-lbs.
With respect to the double spiroid gear samples, the average (of six samples) maximum load at failure was found to be 73.7 lbs. This corresponds to an average torque limit for the double spiroid gear of 73.7×2.5×19=3500.75 in-lbs.
And with respect to hybrid spiroid and worm gear samples, the average (of six samples) maximum load at failure was found to be 83.48 lbs. This corresponds to an average torque limit for the hybrid spiroid and worm gear of 83.48×2.5×19=3965.3 in-lbs.
As can be seen from the test results, the maximum load of at least one embodiment of the hybrid gear, compared to that of similar size and material gears, is considerably higher than the comparable worm gear (e.g., over 470 percent) and higher than the comparable double spiroid gear (e.g., 13.3 percent). Thus, the illustrated hybrid spiroid worm gear has been found to provide a significant increase in torque capability for gearing, without increasing the size of the gears.
It will be understood by those of ordinary skill in the art that the illustrated hybrid enveloping spiroid and worm gear assembly 10 permits a gear application in those instances where high torque handling is required and a physically small gear set is needed. The hybrid enveloping spiroid and worm gear assembly 10 can be formed from polymeric (e.g., plastic, resin) materials and still withstand high or out of the ordinary loads such as thrust loads (longitudinally along the pinion or normal to the gear assembly axis), without stripping the gear teeth 16, 18. It has also been found that higher torque loads can be accommodated since the load is distributed over both the spiroid gear surfaces 24, as well as the worm gear 26.
The opposing gear surfaces 1012, 1014 have the teeth 1016, 1018 that extend from an outer periphery 1022 of each gear surface 1012, 1014 and partially downward toward the central hub region 1020 and other gear surface 1012, 1014. In the illustrated embodiment, the opposing surfaces 1012, 1014 are formed with a spiroid gear form 1024, but the central hub region 1020 is not formed with any gear form. For example, the central hub region 1020 may not have any teeth to mesh with a worm gear, unlike the gear assembly 10 shown in
In the illustrated embodiment, in contrast to the pinion 34 (shown in
The gear assembly 1000 may operate in a manner similar to the gear assembly 10 shown in
In order to create the gear assembly 1000, a single piece body or blank may be cut with a hob device, or hobbing tool. The hob device may concurrently or simultaneously cut the teeth 1016, 1018 of the gear assembly 1000 in the opposing surfaces 1012, 1014 of the single piece blank, as described below.
The blank 1400 includes the opposing surfaces 1012, 1014 from which the teeth 1016, 1018 (shown in
In one embodiment, because the gear assembly 1000 is cut from the single piece blank 1400 and is not formed from two or more separately formed pieces that later joined together, the gear assembly 1000 may be made from a wider range of materials than the gear assembly 10. For example, the gear assembly 1000 may be formed from stronger and/or lighter materials that typically are not joined together to form a larger body, such as aluminum, aluminum bronze, and the like. Other examples of materials include ductile iron, steel, high strength heat treated alloy steels, plastics, and the like.
During cutting of the single piece blank 1400, the hob 1500 is placed between the surfaces 1012, 1014 of the single piece blank 1400. The hob 1500 may be oriented at a skew angle that is similar to the orientation of the pinion 34 with respect to the gear assembly 10 shown in
During the cutting of the teeth 1016, 1018 in the single piece blank 1400, the hob 1500 is positioned so that the cutting teeth 1502 in the cutting segment 1506 engage the surface 1012 of the blank 1400 while the cutting teeth 1504 in the cutting segment 1504 engage the opposing surface 1014 of the blank 1400. In one embodiment, the middle or interconnecting segment 1508 of the hob 1500 may engage the center hub region 1020 of the blank 1400. Alternatively, the middle or interconnecting segment 1508 of the hob 1500 may be spaced apart from the center hub region 1020 of the blank 1400. The hob 1500 may rotate about (e.g., around) the axis of rotation 1602 while the blank 1400 rotates about the axis of rotation 1006 to simultaneously or concurrently cut the teeth 1016, 1018 in the opposing surfaces 1012, 1014 of the blank 1400. Once the hob 1500 has cut the teeth 1016, 1018 into the blank 1400 around the axis of rotation 1006 of the blank 1400, the gear assembly 1000 is formed, as shown in FIG. 17. The hob 1500 may be moved away from the surfaces 1012, 1014 of the gear assembly 1000 and removed from between the surfaces 1012, 1014. In one embodiment, because the hob 1500 does not include cutting teeth 1502 in the middle or interconnecting segment 1508, the center hub region 1020 of the gear assembly 1000 does not include teeth, as described above.
Forming the gearing assembly 1000 using the dual thread cutting hob 1500 can allow for a wider range of materials to be used in the gearing assembly 1000. As described above, materials that typically cannot be easily welded or securely fastened to each other can be used because the teeth 1016, 1018 of the gearing assembly 1000 are formed by cutting into a single piece body 1400.
Simultaneously or concurrently cutting the teeth 1016, 1018 into the opposing surfaces 1012, 1014 of the gear assembly 1000 can improve the timing (e.g., relative spacing) of the teeth 1016 and the teeth 1018 compared to separately cutting the teeth 1016 during one cutting procedure and cutting the teeth 1018 during a separate cutting procedure. The timing (e.g., spacing) of the cutting teeth 1502 of the hob 1500 can be the same as the timing of the teeth of the pinion 1034 such that the simultaneous or concurrent cutting of the teeth 1016 and the teeth 1018 on the opposing surfaces 1012, 1014 automatically aligns the teeth 1016 and the teeth 1018 with the teeth of the pinion 1034 during a single cutting operation. The improved timing of the gear assembly 1000 can reduce backlash relative to gear assemblies having the teeth 1016 and the teeth 1018 separately cut or formed. For example, the backlash can be reduced to 0.013 millimeters or less. Alternatively, the backlash can be reduced to a smaller distance.
At 1904, a hob is positioned between the opposing surfaces of the single piece blank. For example, the hob 1500 (shown in
At 1906, the hob and blank are rotated about respective axes of rotation to cut the teeth into the opposing surfaces of the blank. For example, the hob 1500 can be rotated about the axis of rotation 1602 (shown in
It will be understood by those of ordinary skill in the art that the illustrated enveloping gear assemblies 10, 1000 permit a gear application in those instances where high torque handling is required and a physically small gear set is needed. The enveloping gear assemblies 10, 1000 can be formed from a variety of materials and still withstand high or out of the ordinary loads such as thrust loads (longitudinally along the pinion or normal to the gear assembly axis), without stripping the gear teeth 16, 18, 1016, 1018. It has also been found that higher torque loads can be accommodated since the load is distributed over both the spiroid gear surfaces 24, 1024.
Although not exhaustive nor limiting, it is anticipated that the illustrated gear systems can be used in a variety of applications, including (medical) pump and valve applications, aerospace systems and robotics applications, automobile and transportation systems, power systems, wind energy, mining systems, as well as general manufacturing uses.
All patents referred to herein, are hereby incorporated herein by reference, whether or not specifically done so within the text of this disclosure.
In the disclosures, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular.
From the foregoing it will be observed that numerous modification and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the presently described inventive subject matter. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.
It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the inventive subject matter without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the inventive subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to one of ordinary skill in the art upon reviewing the above description. The scope of the inventive subject matter should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.
This written description uses examples to disclose several embodiments of the inventive subject matter and also to enable one of ordinary skill in the art to practice the embodiments of inventive subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the inventive subject matter is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
The foregoing description of certain embodiments of the present inventive subject matter will be better understood when read in conjunction with the appended drawings. To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. Thus, for example, one or more of the functional blocks (for example, processors or memories) may be implemented in a single piece of hardware (for example, a general purpose signal processor, microcontroller, random access memory, hard disk, and the like). Similarly, the programs may be stand alone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. The various embodiments are not limited to the arrangements and instrumentality shown in the drawings.
This application is a continuation-in-part of U.S. patent application Ser. No. 13/255,655, filed 5 Jan. 2012 (the “'655 application”), which claims priority to U.S. Patent Application Ser. No. 61/158,801, filed 10 Mar. 2009 (the “'801 application”). The entire disclosures of the '655 application and the '801 application are incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13255655 | Sep 2011 | US |
| Child | 13467445 | US |
