Patent Application
20120000305
The present invention relates to an enveloping gear arrangement and more particularly, to an enveloping gear arrangement that uses a spiroid and worm 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—straight gears, angle gears, bevel gears, worm gears, combinations of these and others. Also known are SPIROID® brand gears that use a curved gear tooth. Such a configuration 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 must withstand high loads (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 must be balanced against the size requirements, or conversely the size limitations, of the gear assembly. While the spiroid gear accomplishes this, at times, even smaller size requirements must be met. One such gear tooth form is disclosed in Saari, U.S. Pat. No. 3,631,736, commonly assigned with the present application and incorporated herein by reference.
Accordingly, there is a need for a gear system that can withstand high loads/forces in a limited or small size application. Desirably, such a gear can be formed from non-metallic, e.g., polymeric materials.
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.
It has been found that the present hybrid spiroid and worm gear provides a significant increase in torque capability for gearing without increasing the size of the gears.
In a preferred embodiment, 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.
A present gear body is formed as two parts joined to one another at the hub. The two parts can be substantially identical to one another. The parts can be joined by press-fitting, welding, adhesive, fasteners or the like.
The worm gear 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.
A preferred gear is formed from a polymeric material, such as acetal material or the like.
The hybrid spiroid and worm gear is 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 and an intermediately disposed, second thread form configured to mesh with the gear worm teeth. The pinion first and third thread forms are preferably identical. The second thread form can be different from or identical to the first and third thread forms. The first, second and third thread forms can also be formed as a continuous thread form in the pinion.
One method for making the hybrid spiroid and worm gear is to form the first gear body part, form the second gear body part and join 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.
These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims.
The benefits and advantages of the present invention 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 present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated.
It should be understood that the title of this section of this specification, namely, “Detailed Description Of The Invention”, 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 a present hybrid spiroid and worm gear 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 24 and worm 26 gear forms. The spiroid gear form 24 has a curved tooth profile as indicated at 28. In the illustrated embodiment, the worm gear 26 has lower gear tooth profile. It will, however, be appreciated that the worm gear 26 tooth profile can be the same as the spiroid 24 profile insofar as the pitch, tooth height and 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 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. Alternately, the pinion can be formed tapering (with a decreasing diameter) toward the center of the pinion from the ends, as indicated at P in
As seen 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 maximum torque at failure which was determined to be when the gear teeth fail under applied torque.
Testing was carried out using an ITW Intron device T as illustrated, in part, in
The force was increased slowly until the gear teeth failed.
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 the present hybrid gear, compared to that of similar size and material gears is considerably higher than the comparable worm gear (over 470 percent) and higher than the comparable double spiroid gear (13.3 percent). Thus, the present 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 skilled in the art that the present 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. Importantly, it has been found that the present 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.
Although not exhaustive nor limiting, it is anticipated that the present hybrid enveloping spiroid and worm gear system 10 can be used in (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 present invention. 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.
This application claims the benefit of priority of Provisional U.S. Patent Application Ser. No. 61/158,801, filed Mar. 10, 2009.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US10/23896 | 2/11/2010 | WO | 00 | 9/9/2011 |
| Number | Date | Country | |
|---|---|---|---|
| 61158801 | Mar 2009 | US |
