WO2001029449A1

WO2001029449A1 - Worm/worm gear transmission

Info

Publication number: WO2001029449A1
Application number: PCT/US1999/024199
Authority: WO
Inventors: Yakov Fleytman
Original assignee: Yakov Fleytman
Priority date: 1999-10-15
Filing date: 1999-10-15
Publication date: 2001-04-26
Also published as: JP2003515064A; AU1208000A; KR20020065483A; EP1222412A1; EP1222412A4; CA2387678A1

Abstract

A worm/worm gear transmission (10, 16) includes an enveloping-type worm gear (16) having less than twenty-four teeth which are generated by an enveloping thread (12). The angle of one revolution of the thread has more than 15 degrees. Different profiles of the worm gear (16) are generated by a modified worm thread (12).

Description

TITLE: WORM/WORM GEAR TRANSMISSION

FIELD OF THE INVENTION

The present invention relates generally to speed reducers, and more particularly to those with very low ratios and a unique worm/worm gear transmission which is able ^'to transmit higher torque levels and provide more efficient motion than prior art transmission devices. This invention relates also to a combined transmission system that transmits input mechanical power into a unidirectional output. For this purpose, there are two main systems available:

(i) mechanical oscillating energy is transmitted to the input and the transmission device provides a unidirectional energy to the output; and (ii) continuous unidirectional mechanical energy is transmitted to the input and the transmission device changes the speed to the output . We can make an analogy with electrical energy, where two sources of energy, direct and alternative current, are available, but an electric motor using this energy has unidirectional motion.

BACKGROUND

Transmissions are utilized to transmit rotation for a variety of purposes. The term "transmission" as utilized in this application, does not specifically refer to a vehicle transmission, although it would extend to such transmissions. Rather, this invention extends to any system wherein a source of movement is transmitted through a driving member to move a driven member. One potential application for this transmission is a helicopter rotor drive. As is known, one of the biggest problems associated with helicopter rotor drives is noise. When compared to conventional non-parallel shaft gear transmissions, worm/worm gear type transmissions generate minimum noise. However, low efficiency and torque capacity associated with prior art worm/worm gear transmissions prevented their use in helicopter power transmission systems.

Worm/worm gear transmissions, in particular double enveloping speed reducers or cone drive worm/worm gears, are well known in the mechanical power transmission field. The worm gear is driven by the rotation of the worm with which it meshes. The rotational speed of the associated shaft of the worm gear is a function of the number of teeth on the worm gear and the number of threads on the worm. The worm may be single or multiple threaded. The prior art worm/worm gear transmission had a worm gear with twenty-four or more teeth. In particular, the American National Standard "Design of Industrial Double-Enveloping Wormgears" (ANSI/AGMA-6030-C87) recommends twenty-four as the minimum number of gear teeth. Furthermore, the enveloping angle of any known worm gear for one revolution of the thread of the worm is not more than 15 degrees.

In all standard double enveloping worm/worm gear transmissions, the enveloping worm gear has a surface that is generated by the profile of an enveloping thread of the worm. The term "generated" describes how the profile of the worm gear tooth can be defined. It could utilize mathematical calculations defining the profile from equations of the surface of the enveloping worm thread; hobbing of a gear blank by a tool having the profile of the worm thread; or via computer modeling where the profile of a three-dimensional solid worm gear is cut by the profile of a three-dimensional solid worm thread. Conventional enveloping worm/worm gear transmissions did not use worm gears with less than twenty- four enveloping type gear teeth due to the undercut on the root of the tooth. The enveloping angle of the worm is the angle of area contact between the threads on the worm and worm gear teeth. The enveloping angle is the angle between the ends of the worm thread defined with reference to the center of the worm gear. For a worm with one revolution of thread, the maximum number of engaging gear teeth is two. As is known, the enveloping thread angle can be calculated by the equation: φ = 360°/N where N is the number of worm gear teeth.

Thus, for 24 teeth, φ₂ = 15°. Likewise, for 12 teeth (pι₂ = 30°. This angle is also equal to the angular pitch for the worm gear .

If we use a two thread worm, then the enveloping angle should be twice as big as the angular pitch of the worm gear. For example, an enveloping angle of a single thread worm for a worm gear with six teeth is 60 degrees while the enveloping angle of a double thread worm for a worm gear with six teeth is 120 degrees. Thus, for multiple thread worms, the enveloping angle is calculated by the equation φ = t * 360°/N, where t equals the number of threads.

In all standard enveloping worm/worm gear transmissions, only a line contact exists between the worm thread and the worm gear teeth.

Moreover, standard double enveloping worm/worm gear transmissions have been used only for ratios of five and more. Due to such high ratios, it has been considered impractical to use the worm gear as the driven member and the worm as the driving member to transfer power from the worm gear to the worm. In transmitting continuous unidirectional energy and changing the ratio by using self-locking properties of the worm/worm gear transmission, there are many different modifications in the prior art.

In general, -the prior art uses combinations of a strait worm and worm gear with combinations of differential means.

Examples of these transmissions are in U.S. Patent Nos. 2,853,140 to Else; 2,225,957 to Korff; 3,208,305 to Butterbaugh; 4,346,728 to Harry; 4,917,200 to Lucius; 4,346,728 to Sulzer; 4,987,788 to Bausch; 4,973,295 to Lee; Re33,278 to Johnshoy; 3,220,284 to Horvath; 5,033,996 to Frey; and 5,015,898 to Frey.

In order to provide self-lock, it is better to use a worm with only one thread because it makes the lead angle smaller. In previous art with a strait worm, it was possible by making more than one revolution of the thread. This design resulted in only two worm gear teeth and threads being in mesh. When the total worm gear teeth are more than twenty-four, it makes each tooth small and limits the load capacity. The minimum ratio in previous self-locking worm systems with one thread is 24. With these systems, the worm speed is 24 times greater than the speed of the worm gear. This is why the previous art was not utilized in real life applications. Increasing the size of the worm pitch diameter to make comparable with the worm gear pitch diameter was also unpractical because it makes very small threads relative to the big body of the worm. Using standard double enveloping worm/worm gear transmissions having more than 24 worm gear teeth and an enveloping angle for one revolution of a worm thread which is less than 15 degrees has the same problem. Specifically, small and weak teeth and a high ratio of worm gear teeth to threads of more than 24.

SUMMARY OF THE INVENTION

Enveloping worm/worm gear transmissions having less than twenty-four teeth, have not been commercially used since it was universally believed that it was not possible to build such a transmission due to undercut on the root of the worm gear tooth. Up to now, those skilled in the art were skeptical that an enveloping type worm gear with less than twenty-four teeth was workable or presented an insurmountable barrier. In contrast, the enveloping worm/worm gear transmission of the present invention utilizes a worm gear without undercut gear teeth because of a greater enveloping angle for one revolution of the worm thread.

With less than twenty- four gear teeth and a greater enveloping angle for one revolution of the thread, as compared to prior enveloping worm/worm gear transmissions, the minimum ratio for one thread could be reduced to two, with an achieved efficiency for this invention of up to 99 percent. In contrast, prior enveloping worm/worm gear transmissions had a minimum ratio of twenty- four for one thread of the worm and a ratio of five for five threads of the worm. The efficiency of the new worm/worm gear transmission is even greater than in well-known hypoid gearing, which is used in low ratio right angle drives. Thus, the present invention can replace hypoid or bevel gearing in many applications by reason of the low ratio. In addition, this new worm/worm gear transmission is able to back drive by transmitting torque from the worm gear to the worm. For the same size, this invention has more than twice the capacity of traditional hypoid gearing.

In this application, it is possible to have "surface to surface" contact between the worm gear teeth and the worm thread, thereby increasing the torque capacity of the enveloping worm/worm gear transmission. This became feasible when the enveloping angle for one revolution of worm thread is more than 15 degrees. In all standard enveloping worm/worm gear transmissions (Faydor Litvin 1994, Gear Geometry and Applied Theory, PTR Prentice Hall, Englewood Cliffs, New Jersey) , only line contact is obtained between the thread and worm gear teeth or thread followers. This physical distinction has realized new and unexpected results.

In the present invention, the worm can be half or less than half of a split worm, which can have only one supporting shaft. Further, the worm gear can be half or less than half of a split worm gear, which can have only one supporting shaft. Using only half or less than a half of the split worm gear or worm enables easier assembling of the worm with the worm gear. The present invention describes the effect of "self- lock" between a worm and worm gear which is used for designing a one way clutch. The term "self-locking" as is utilized in this application to describe the inventive worm and worm gear combination, requires that the teeth of the worm gear when in contact with the thread of the worm, are incapable of rotating the worm about its axis. The teeth do not slip on the thread causing the thread to rotate about its own axis. By carefully selecting the material of the respective teeth and threads, and the respective angles, a worker of ordinary skill in the art would be able to achieve this goal. Typically, in previous art, free motion of a worm has been provided by an electric motor. This is important for the purpose of reversing the direction of transferring torque, but the worm has to rotate effectively at a rate which is equal to the ratio of the gear teeth and thread of the worm gear and worm. New in this invention are a gear train or pulley drive (flexible shaft is optional) comprising an on/off clutch and input of the train (drive) being driven by said worm gear and the worm being driven from the output of the train (drive) . The worm and worm gear combination is incorporated into a system wherein the worm is mounted for rotation in a rotor. The rotor surrounds a driving worm gear. A rotational input is applied to the worm gear. The worm gear teeth engage the thread on the worm, the worm and the rotor rotate about the axis of the worm gear. This rotation is without relative movement between the engaged teeth of the worm and worm gear.

An auxiliary motor (or an on/off clutch) is preferably mounted on the rotor, and rotates the worm relative to the worm gear to either return the worm gear to its original position, or allow the worm gear to move relative to the worm when an oscillating input is utilized. When subjected to an oscillating input, the worm and rotor act as a mechanical diode, resulting in a single direction output. When we use the motor instead of the gear train comprising an on/off clutch, we need to synchronize on/off action of the clutch according to oscillation of the worm gear.

In describing different versions of transmissions, the base of the design is a grounded rotor which is holding the worm. Due to this, there is no problem connecting the electrical connections to the operative members even when the operative members freely rotate more than 360 degrees. Balancing of the rotor also becomes easy. Versions of designs with a worm gear attached to the different members of the spider differential and bevel differential are the foundations of the invention. Transmissions with different ratios are provided as combinations of these designs. Examples, shown in this patent application are not described in the parent patent application. The usage of this invention not only transmits the rotation utilizing an oscillating input but also transmits the torque for the conventional power transmission. For example, this system can be utilized as part of a vehicle transmission or a gear box with changeable ratio.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: Figure 1 is a cross-sectional view of a worm/worm gear transmission with the worm gear having three teeth according to the principles of the present invention;

Figure 2 is a side view of a worm/worm gear transmission with the worm gear having six teeth according to the principles of the present invention;

Figure 3 is a side view of the worm/worm gear transmission with the worm gear being shown in cross- sectional view;

Figure 4 is a side view of an enveloping worm with two threads for generation of a profile of a worm gear;

Figure 5 illustrates the use of an enveloping thread for the generation of the profile of the teeth of the worm gear;

Figure 6 is a view of a shortened thread for the generation of a profile of the teeth of the worm gear;

Figure 7 is a side view of an enveloping worm gear according to the principles of the present invention;

Figure 8 is a side view of a modified worm gear with driving shaft having support from one side of the worm gear;

Figure 9 shows a side view of a worm/worm gear transmission with modified worm;

Figure 10 is a side view of a worm/worm gear transmission with a driving shaft having support from one side of the worm; Figure 11 shows a side view of a worm/ orm gear transmission with a modified worm in an off-center position;

Figure 12 shows a side view of a worm/worm gear transmission with two modified worms in off-center position;

Figure 13 shows a side view of a worm/worm gear transmission with two modified worms placed on the same axis of rotation and connected to the same drive shaft; Figure 14 shows a side view of a worm/worm gear transmission with two modified worms placed on different axes of rotation;

Figure 15 shows an enveloping worm gear with a different profile of teeth; Figure 16 shows a side view of a worm/worm gear transmission with two enveloping worms placed on different axes of rotation;

Figure 17 is a perspective view of the worm/worm gear transmission shown in Figure 1 with three worm gear teeth; Figure 18 is a perspective view of the worm/worm gear transmission shown in Figure 2 with six worm gear teeth and two threads on the worm;

Figure 19 is a perspective view of a worm/worm gear transmission with ten worm gear teeth and with a single thread worm;

Figure 20 is a perspective view of a worm/worm gear transmission with nine worm gear teeth and a modified worm having three threads on the worm;

Figure 21 is a perspective view of a worm gear with six teeth with darkened spots illustrated on the surface of the teeth to illustrate the contact surface with the worm in mesh;

Figure 22 is a perspective view of a worm with two threads with darkened spots illustrated on the surface of the thread to illustrate the contact surface with the worm gear in mesh;

Figure 23 illustrates the size difference of the worm/worm gear transmission of Figure 20 in comparison to the size of a typical hypoid type gear; Figure 24 is a cross-sectional view of a worm/worm gear transmission of the present invention with a gear train comprising an on/off clutch;

Figure 25 is a cross-sectional view of a worm/worm gear transmission of the present invention with a gear train comprising the on/off clutch and a flexible shaft;

Figure 26 is a cross-sectional view of a worm/worm gear transmission of the present invention with a pulley drive comprising the on/off clutch and the flexible shaft; Figure 27 is a cross-sectional view of a spider differential with a sun gear being connected to a worm/worm gear transmission incorporating the principles of the present invention;

Figure 28 is a cross-sectional view of a spider differential comprising a ring gear and with a sun gear being connected to the worm gear of a worm/worm gear transmission according to the principles of the present invention;

Figure 29 is a cross-sectional view of a spider differential with the ring gear being connected to the worm gear of a worm/worm gear transmission according to the principles of- the present invention; Figure 30 is a cross-sectional view of a spider differential with the carrier being connected to the worm gear of a worm/worm gear transmission according to the principles of the present invention; Figure 31 is a cross-sectional view of a spider differential comprising a ring gear with the carrier being connected to the worm gear of a worm/worm gear transmission according to the principles of the present invention; Figure 32 is a cross-sectional view of a bevel differential with a bevel gear connected to the worm gear of a worm/worm gear transmission according to the principles of the present invention;

Figure 33 is a cross-sectional view of a bevel differential with a carrier being connected to the worm gear of a worm/worm gear transmission according to the principles of the present invention;

Figure 34 is a cross-sectional view of a bevel differential with the carrier being connected to a first worm gear and the bevel gear being connected to a second worm gear of a pair of worm/worm gear transmissions according to the principles of the present invention;

Figure 35 is a cross-sectional view of a spider differential with the carrier being connected to the first worm gear and the sun gear being connected to the second worm gear of a pair of worm/worm gear transmissions according to the principles of the present invention;

Figure 36 is a cross-sectional view of a spider differential with the sun gear being connected to the first worm gear and the ring gear being connected to the second worm gear of a pair of worm/worm gear transmissions according to the principles of the present invention;

Figure 37 is a cross-sectional view of a spider differential with the carrier being connected to the first worm gear and the ring gear being connected to the second worm gear of a pair of worm/worm gear transmissions according to the principles of the present invention;

Figure 38 is a cross-sectional view of a spider differential with the carrier being connected to the first worm gear and the sun gear being connected to the second worm gear of a pair of worm/worm gear transmissions according to the principles of the present invention with a gear train comprising an on/off clutch; Figure 39 is a cross-sectional view of a spider differential with the carrier being connected to the first worm gear and the sun gear being connected to the second worm gear of a pair of worm/worm gear transmissions according to the principles of the present invention with means, comprising a gear train with an on/off clutch and an auxiliary motor;

Figure 40 is a cross-sectional view of the bevel differential with the sun gear being connected to the first worm gear and the ring gear being connected to the second worm gear of a pair of worm/worm gear transmissions according to the principles of the present invention;

Figure 41 is a cross-sectional view of a bevel differential being connected to the first worm gear and the second worm gear of a pair of worm/ orm gear transmissions according to the principles of the present invention with one fixed rotor; Figure 42 is a cross-sectional view of the spider differential and bevel differential being connected to the first worm gear and the second worm gear of a pair of worm/worm gear transmissions according to the principles of the present invention with two fixed rotors;

Figure 43 is a cross-sectional view of the worm gear with the teeth engaging the thread on a part of split worm of a worm/worm gear transmission according to the principles of the present invention; Figure 44 is a cross-sectional view of congruent surfaces of the lands on the half of the worm and the teeth of the worm gear;

Figure 45 is a cross-sectional view of a split worm and worm gear with a train of a torsion spring with a friction clutch;

Figure 46 is a cross-sectional view of two split worms and a worm gear with two trains of the torsion spring with the friction clutch;

Figure 47 is a side view of a worm/worm gear transmission with the worm being bodiless;

Figure 48 is a side view of a bodiless enveloping worm as shown in Figure 47;

Figure 49 is a side view of a bodiless enveloping worm with a support member being provided to support the worm threads;

Figure 50 is a side view for a bodiless part of split worm having a support member to support the ends of the worm threads ; and

Figure 51 is a perspective view of a double enveloping worm/worm gear transmission illustrating the orientation of the worm and worm gear for engagement with one another. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of a worm/worm gear transmission 8 of the present invention is illustrated in Figure 1. The transmission has an enveloping type worm 10 with at least one screw thread 12. The enveloping type worm 10 is supported on a shaft 13. Thread 12 is engaged by at least one tooth 14 of an enveloping type worm gear 16 having three teeth 14. As shown in Figure 1, the enveloping worm 10 has a single thread 12 in a preferred embodiment and the worm gear 16 has three teeth 14 spaced about its circumference. As shown, a gap "G" exists between any tooth on worm gear 16 and threads on enveloping worm 10. Enveloping worm 10 wraps around enveloping worm gear 16, and enveloping worm gear 16 also wraps around enveloping worm 10.

According to the principles of the present invention, the minimum ratio between the number of teeth on the worm gear and the one thread on the worm is two. Accordingly, by rotation of the worm gear, the worm rotates with higher speed. Worm gear 16 and worm 10 are preferably enclosed in a housing (not shown) in Figure 1. Typically, the housing is made from metal and forms a reservoir for a lubricant to both lubricate and cool the gears, bearings, and seals for the unit. The housing forms a rigid support to mount the gears, bearings, seals and their associated parts (not shown) .

Figure 17 is a perspective view which corresponds with the worm/worm gear transmission 8 shown in Figure 1 which includes an enveloping worm 10 having a single thread 12 and a worm gear 16 having three gear teeth 14.

As can be understood, as the worm 10 rotates in the direction of Arrow A, the thread 12 which is engaged with tooth 14a presses downward on the tooth 14a to cause rotation of worm gear 16 in the direction of Arrow "B" . As the worm gear 16 rotates, gear tooth 14b then comes into engagement with the thread 12 and is acted on to cause further rotation of the worm gear 16 as the gear tooth 14a disengages from the thread 12.

The reason for using an enveloping-type of worm gear is that this type of worm gear has a natural profile of tooth surface which is distinct from other types of thread followers. The configuration of the worm gear teeth is generated by the profile of the thread or threads of the worm. A computer model simulation can be utilized to generate the configuration of the worm gear teeth of the worm gear. The worm gears can then be formed using known techniques such as hobbing or casting. When the worm gear teeth are generated by the profile of the threads of the worm having different lengths for the same enveloping angle (shortened) , the profiles of the worm teeth is different . The main advantage for using the enveloping-type of worm gears is more torque capacity. The worm thread has a rolling action contact relationship with the teeth of the worm gear which provides an increased efficiency. Furthermore, it is beneficial to have the pitch diameter in the center portion of the worm on the same order as the pitch diameter in the center of the worm gear. With standard worm designs, having more than one thread and a large enveloping angle, the inability to assemble the worm and worm gear was considered a major obstacle. With the worm and worm gear of the present invention, the worm and worm gear are easily assembled by properly orienting the worm thread and worm teeth as illustrated in Figure 51. Specifically, the worm 160 having two threads 162 is shown oriented so that a worm gear tooth 164 is brought directly into engagement with the worm threads 162 from a radial direction so that the two adjacent worm gear teeth 166, 168 are brought only into partial engagement with the threads 162 from one side (166A, 168A) of the gear teeth 166, 168 of the worm gear 170. The distance between the threads 162 is large enough to receive the teeth of the worm gear 170 when brought directly into engagement. Another embodiment of the worm/worm gear transmission 20 of the present invention is illustrated in Figure 2. This transmission has an enveloping worm 22 with two identical screw threads 24. These threads 24 are engaged by at least one tooth of an enveloping-type worm gear 26 having six teeth 28. Worm gear 26 is connected to a shaft 30 while worm 22 is connected to a shaft 32. In Figure 3, the worm gear 26 is shown in cross-section. Figure 4 is a side view of the enveloping worm 22 with two identical threads 24 and supporting shaft 32. Figure 18 is a perspective view which corresponds with the worm/worm gear transmission shown in Figure 2 which includes an enveloping worm gear 26 having six teeth 28 meshing with an enveloping worm 22 having two threads 24. Figure 5 shows an enveloping angle of 120 degrees for the enveloping worm thread 24 that is used for generation of the six teeth 28 on worm gear 26. This enveloping worm thread 24 has one revolution of thread or 360 degrees of revolution around its axis of rotation. For illustration of one revolution for the enveloping worm thread, we could use this example: the worm thread's ends have the same cross-sections but could be placed from one position to another position, which is a distinct 120 degrees. This is possible by movement of the cross-section of the worm from one end along the worm thread 24 to another end. In this case, the cross-section will rotate 360 degrees around the axis of rotation for shaft 32.

The enveloping worm/worm gear transmission of the present invention provides for a worm gear having fewer than twenty-four teeth and also provides surface contact between the thread of the worm and the teeth of the worm gear as illustrated in Figures 21 and 22. Figure 21 illustrates two surface contact spots 100a, 100b for a worm gear 26 having six teeth 28. Figure 22 illustrates two corresponding surface contact spots 102a, 102b for a worm 22 with two threads 24. Figure 6 shows a worm thread 38 for generation of worm gear teeth which is a shortened portion of a thread having an enveloping angle of 120 degrees.

Figures 7 shows a side view of the enveloping worm gear 26 with six teeth 28. Figure 8 shows an enveloping worm gear 44 having six teeth 34 which is modified from the worm gear 26 shown in Figure 7 by shortening the gear along its axis of rotation around drive shaft 46. Practically, the worm gear 44 could be longitudinally split into two halves and using only one shortened part or generated worm gear from blank, which is already shortened. Modified worm gear 44 is easy to assemble in a single reduction unit. This is very important for gears with a small pressure angle when it is difficult to assemble an enveloping worm with an enveloping type of worm gear. For many applications, only the modified worm gear 44 is enough. The enveloping worm gear 44 could connect to a drive shaft 46 for supporting the worm gear 44 from only one side or could be supported on both sides .

The bodies of the enveloping worm gears 26 and 44 have axially extending end flanges that hook underneath flanges of adjacent collars to hold the worms in place. One or both of the worm and worm gear bodies are keyed or otherwise fastened to the shaft for driving or being driven. Relatively slight longitudinal movement of one or both the worm or worm gear allows for disassembling the entire worm gear - collars - shaft assembly.

In the present invention, it is preferred that the ratio of the number of teeth 14 on the worm gear 16 relative to the number of threads 12 on the worm 10 is 11 to 1 and less. Most preferably, the ratio is three or even less, as shown. It is possible that only two teeth 14 need to be utilized on worm gear 16. The worm/worm gear transmission used in the present application could also self lock.

The term "self-locking" as it is utilized in this application to describe the inventive worm and worm gear combinations, means that the teeth of the worm gear, when in contact with the thread of the worm, are not capable of rotating the worm about the axis of the worm. The teeth 14 do not slip on the thread 12 causing the thread 12 to rotate about its own axis. By carefully selecting the material of the respective teeth 14 and threads 12, and the respective angles, a worker of ordinary skill in the art would be able to achieve this goal . The worm/worm gear transmission of the present invention particularly lends itself to a geometric as opposed to a purely frictional type self-locking device. Figure 9 shows a shortened enveloping worm 50 with an enveloping type of worm gear 52, which has a different profile of the teeth 53, compared to the teeth 28 of the worm gear 26 (shown in Figures 2 and 7) even for the same number of worm gear teeth. It is because this profile was generated by a shortened enveloping thread 54 for the shortened enveloping worm 50.

In Figure 10, enveloping worm 50 is connected to a drive shaft 56 which supports the worm 50 from one side. Figure 11 shows a view of a worm/worm gear transmission with the modified enveloping split worm 60 having two threads 61 in an off-center position relative to the enveloping-type worm gear 62 having six teeth 63.

Figure 12 shows a side view of a worm/worm gear transmission with two modified worms 60 having two threads 61 in off-center positions and respectively connected to different drive shafts 62 and 64 and each meshingly engaged with the worm gear 62.

Figure 13 shows a view of a worm/worm gear transmission with two modified worms 60 in off-center positions placed on the same axis of rotation and connected to the same drive shaft 32.

When the modified worms are connected to a common shaft with a different angular phase of the threads, it means that in motion, the threads of one worm are going in mesh with the worm gear teeth and the thread of the other worm are going out from mesh at different times. The purpose of the phase difference is to increase the contact ratio and to provide smooth mesh. Figure 14 shows a view of a worm/worm gear transmission with two modified worms 60 having worm threads 68 each placed on different axes of rotation and connected to different drive shafts 70 and 72. Each of the worms 60 meshingly engage the worm gear 62 having teeth 64.

Figure 15 shows a side view of an enveloping worm gear 62 with a different profile of teeth 64 generated by the enveloping thread 68 of worm 60 as shown in Figure 14. Figure 16 shows a view of a worm/worm gear transmission with two enveloping worms 22 having corresponding worm threads 24 placed on different axes of rotation and which are connected to drive shafts 32. Each of the worms 22 meshingly engage the enveloping worm gear

26.

Figure 19 is a perspective view of a worm/worm gear transmission including worm gear 80 having ten teeth 82 meshing with an enveloping split worm 84 including a thread 86.

Figure 20 is a perspective view of a worm gear 90 having nine teeth 92 meshing with a modified enveloping split worm 94 with three threads 96. Figure 23 illustrates the size difference of a worm/worm gear transmission as shown in Figure 20 in comparison with the size of a typical hypoid gear 106.

For the inventions described in the present patent application, there could be two different types of operations. When the worm/worm gear transmission does not have self-lock, the motion could be provided from the drive shaft through enveloping worm 12 and enveloping-type worm gear 16 to an output shaft or back from the output shafts to the drive shaft 32. The same operation is applicable for motion from the drive shaft to the driven shafts or from the driven shafts to drive shaft of the other embodiments shown. Alternatively, when the worm/worm gear transmission does have self-lock, motion can be provided only from the drive shaft through the enveloping worm and to the enveloping type worm gear and to the output shaft. Thus, the worm/worm gear transmissions shown in Figures 12, 14 and 16, with independent drive shafts connected to the worms, could be used in a split-power transmission of a helicopter drive to transmit energy from a high-speed engine to a rotor drive shaft. In this case, the worm gear could be connected directly (or by gear train) to the helicopter rotor drive shaft, and worms could be connected to the output of the helicopter engine directly (or by gear train) . In some designs of helicopter power train, the worm/worm gear transmission of the present invention could replace bevel gears.

According to the present invention, the greater enveloping angle for one revolution of the worm thread permits the use of worm gear teeth without undercut portions . In one feature of the present invention, a worm and worm gear combination are utilized to transmit rotation with the smallest ratio between the worm gear teeth and one worm thread. In the past, it has been believed that at least 24 teeth were required for a worm gear to be used with a double enveloping worm/worm gear combination.

However, in the present invention, the big difference from the traditional worm/worm gear is not only in the number of teeth, but also in the enveloping angle of the worm thread, which is used for generation of the profile for the worm gear teeth. This enveloping angle can be as large as 180 degrees for one revolution of the thread when the number of worm gear teeth is only 2 but is preferably larger than 15 degrees.

In the present invention, a self-locking worm/worm gear combination can have a worm gear to worm thread ratio that is preferably 10 and less.

Such a system is desirable so that each one of the worm and worm gear combinations described above can transmit very high torque loads when compared to prior systems . In the past, the worm and worm gears have been formed of materials having low coefficients of friction; worm gears typically were made only from bronze. With the present invention however, the worm and worm gear could be made from a strong material such as steel . The preferable shape of the teeth and threads for the worm gear and the worm is shown in the drawings, but could be different. Even so, a worker of ordinary skill in the art would recognize that other shapes would come within the scope of this invention. In the present application, it is surface-to-surface rolling contact between the worm gear teeth and the worm thread that increases the torque capacity of the enveloping worm/worm gear transmission. This became possible when the enveloping angle of the worm thread for generation of the worm gear teeth is more than 15 degrees, or even 30 degrees. The efficiency of the new worm/worm gear transmission is equal or even greater than in well- known hypoid gearing, which are used in right angle drives with low ratio. For back drive, when the worm gear is a driven member and the worm is a driving member, this worm/worm gear transmission also has high efficiency compared to a hypoid gear set . It was confirmed by dyno testing of a steel worm/worm gear transmission according to the present invention that the present invention can replace hypoid or bevel gearing in many applications. The lower noise of the worm/worm gear transmission compared with hypoid and bevel gear transmissions make using the worm/worm gear transmission of the present invention more beneficial, in particular, in helicopter or car power train applications. For the same size, this invention has more than twice the capacity of hypoid gearing, where the hypoid gear also has more than 24 teeth. The smaller number of teeth of the present invention than in a hypoid gear of the same circumference makes each tooth thicker and therefore stronger. In the illustration shown in Figure 23, we can see a modified worm 94 with three threads 96 which has a shape and size similar to a pinion of a hypoid transmission. For the same size of the modified worm 94 and the pinion of the hypoid gear 106 the diameter of the hypoid gear 106 is twice the diameter of the worm gear 90. Up to now, those skilled in the art were skeptical that an enveloping type worm gear with less than twenty-four teeth would work and/or present an insurmountable barrier in commercial applications .

With reference to Figures 47-50, a bodiless enveloping worm 200 is shown having threads 202 in meshing engagement with an enveloping worm gear 204. The threads 202 of the enveloping worm 200 are supported at opposite ends (202A, 202B) thereof by support members 206. The threads 202 can be integrally formed with the support members 206 by casting or machining, or can be welded to the support members 206 or attached by other known techniques. In the embodiment shown in Figures 47 and 48, a full enveloping worm is provided with threads 202 connected to support members 206. Figure 49 illustrates an additional support disk 208 used for connecting between the threads 202 at an intermediate position between the two ends (202A, 202B) of the threads 202. The support disk 208 adds additional strength and rigidity to the threads 202.

Figure 50 illustrates a bodiless split enveloping worm 212 having threads 214 connected to a base support member 216 and to an end support member 218. The bodiless split enveloping worm 212 is supported for rotation by the base support member 216. The bodiless enveloping worm designs as described above provide a flexible worm which is capable of absorbing torsional spikes to the worm/worm gear transmission. In addition, the bodiless enveloping worm designs lend themselves to improved lubrication along the entire length of the threads.

The basic inventive system of the present invention can be reconfigured into many different mechanical transmissions. For example, it can be used in a front axle drive and differential drive rear axle of a car, power windows, escalator drive and more.

The enveloping worm and worm gear as described above can be utilized in an apparatus for transmitting rotation utilizing an oscillating input as shown in Figure 24. The apparatus includes a worm 111 which is enclosed in a rotor 112. The rotor 112 forms a rigid support to mount bearings. For best results, the worm 111 is enveloping and wraps around worm gear 113. The worm gear 113 is also enveloping and wraps around the worm 111. During the rotation of the worm 111, the worm gear 113 rotates with low speed. The minimum ratio between the number of worm gear teeth and one worm thread provided on the worm 111 is two (2) . On the other hand, by rotation of the worm gear 113, worm 111 rotates with higher speed. This invention comprises means for rotating the worm 111 about its axis of rotation relative to the worm gear 113. Said means can be the auxiliary motor or in a gear train comprising a hypoid-gear set, spiroid-gear set, bevel- gear set or helicon-gear set, may consist of gears 116, 117 with the on/off clutch 118. Input of the train is driven by the worm gear 113 from the input shaft 114 and the worm 111 is driven by the output (on/off clutch) of the train. The rotor 112 is connected to the output shaft 115. On/off clutch 118 can be a friction electromechanical clutch with natural conditions like "on" or "off" . The ratio of the train is more or equal to the ratio between the number of teeth on the worm gear 113 relative to the threads on worm 111. The worm 111 and worm gear 113 have the property of self-lock.

Examples of drive means for rotating the worm 111 about its axis of rotation relative to the worm gear 113 are shown in Figure 25 and Figure 26. The means as disclosed in Figure 25 is a gear train comprising spur gears 119, 120, flexible shaft 121 and the on/off clutch 118. The drive means as disclosed in Figure 26 is a pulley drive comprising pulleys 160, 161 with belt 162, the flexible shaft 161 and the on/off clutch 118. The drive means with flexible shaft 121 is easy to assemble in a single reduction unit. To provide a preload in a direction around an axis of the worm 111 and to eliminate a backlash between the teeth of the worm gear 113 and the thread of the worm 111, it is better to use an auxiliary motor. When the rotor 112 is grounded, the worm gear 113 is connected to one of the members of the differential gear set. As illustrated in Figure 27, the differential gear set is a spider differential comprising sun gears 122, 123 with a spider gear 124, a housing 125 and a carrier 126 wherein the sun gear 122 is connected to the worm gear 113. For simplicity of illustration, the drive means is the auxiliary motor 127.

As illustrated in Figure 28, the differential gear set is a spider differential comprising a sun gear 123, a ring gear 128 with a spider gear 130, a housing 125, and a carrier 126 wherein the sun gear 123 is connected to the worm gear 113.

As illustrated in Figure 29, the differential gear set is a spider differential comprising a sun gear 123, a ring gear 128 with a spider gear 130, a housing 125, and a carrier 126 wherein the ring gear 128 is connected to the worm gear 113.

As illustrated in Figure 30, the differential gear set is a spider differential comprising sun gears 122,

123 with a double spider gear 124, a housing 125, and a carrier 126 wherein the carrier 126 is connected to the worm gear 113.

In an example illustrated in Figure 31, the differential gear set is a spider differential comprising a sun gear 123, a ring gear 128 with a spider gear 130, a housing 125, and a carrier 126 wherein the carrier 126 is connected to the worm gear 113.

As illustrated in Figure 32, the differential gear set is a bevel differential comprising bevel gears 129,

134 with an idler bevel gear 131, a housing 132 and a carrier 133 wherein the bevel gear 134 is connected to the worm gear 113.

As illustrated in Figure 33, the differential gear set is a bevel differential comprising bevel gears 129, 134 with an idler bevel gear 131, a housing 132 and a carrier 133 wherein carrier 133 is connected to the worm gear 113.

As illustrated in Figure 34, the differential gear set is a bevel differential comprising bevel gears 129, 134 with a spider bevel gear 131, a housing 132 and a carrier 133 wherein the carrier 133 is connected to the worm gear 136. Bevel gear 134 is connected to the worm gear 113. An extra shaft 138 can provide an opposite direction of rotation. For simplicity, the drive means are auxiliary motors 127 and 137.

To change the ratio of the transmission or to reverse the direction of rotation, a pair of worms 111 and 135 with the rotors 112 and 127, with each of the worm gears 113, 136 can be driven by independent shafts 114 and 115 and have a differential for connecting the worm gears with members of the differential .

As illustrated in Figure 35, the differential gear set is a spider differential comprising sun gears 122,. 123, 128, with a spider gear 139, a housing 125 and a carrier 126 wherein the sun gear 128 is connected to the second worm gear 136, and the carrier 126 is connected to the first worm gear 113. For simplicity, the drive means are auxiliary motors 127 and 137.

As illustrated in Figure 36, the differential gear set is a spider differential comprising sun gears 122, 123, and a ring gear 128, a housing 125, a spider gear 124 and a carrier 126 wherein the sun gear 123 is connected to the first worm gear 113 and the ring gear 128 is connected to the second worm gear 136. For simplicity the drive means are auxiliary motors 127 and 137. As illustrated in Figure 37, the differential gear set is a spider differential comprising sun gears 122, 123, and a ring gear 128, a housing 125, a spider gear 124 and a carrier 126 wherein the carrier 126 is connected to the first worm gear 113 and the ring gear 128 is connected to the second worm gear 136. For simplicity the drive means are auxiliary motors 127 and 137.

As illustrated in Figure 38, the differential gear set is a spider differential comprising sun gears 122, 123, 128, with a spider gear 139, a housing 125 and a carrier 126 wherein the sun gear 128 is connected to the second worm gear 136 and the carrier 126 is connected to the first worm gear 113. The first drive means are gears 116 and 117 with on/off clutch 118 and the second drive means is auxiliary motor 127.

As illustrated in Figure 39 the differential gear set is a spider differential comprising sun gears 122, 123, and a ring gear 128, a housing 125, a spider gear 124 and a carrier 126 wherein the carrier 126 is connected to the first worm gear 113 and the ring gear 128 is connected to the second worm gear 136. The first drive means are gears 116 and 117 with on/off clutch 118 and the second drive means is auxiliary motor 127.

As illustrated in Figure 40, the differential gear set is a spider differential comprising sun gears 122, 123, and a ring gear 128, a housing 125, a spider gear 124 and a carrier 126 wherein the sun gear 123 is connected to the first worm gear 113 and the ring gear 128 is connected to the second worm gear 136. The first drive means are gears 116 and 117 with an on/off clutch 118 and the second drive means are gears 140, 141 with an on/off clutch 142.

Figure 41 is a combination of Figure 24 and Figure 33. As illustrated in Figure 41, the differential gear set is a bevel differential comprising bevel gears 129 and 134 with an idler bevel gear 131, a housing 132 and a carrier 133 wherein the carrier 133 is connected to the worm gear 113 and to the worm gear 136. The rotor 112 is grounded .

As illustrated in Figure 42, the differential gear set is a spider differential comprising sun gears 122, 123, a housing 125 with a carrier 126 and a bevel differential comprising bevel gears 129, 134 and an idler bevel gear 131, wherein the carrier 126 is connected to the first worm gear 113 and the sun gear 122 is connected to the second worm gear 136 and the carrier 133. The first drive means are gears 116 and 117 with an on/off clutch 118 and the second drive means is drive motor 127.

Figure 43 discloses a split worm 143 enclosed in a rotor 144 and an auxiliary motor 145. For balancing, the body of the rotor 144 holds removable balancing elements 146. Half or less than half of the worm 143 is easy to assemble with a worm gear 147.

Figure 44 is a cross-sectional view of congruent surfaces of the lands on the half of the worm 143 and the teeth of the worm gear 147. Figure 45 is a cross-sectional view of the half worm 143 and the worm gear 147 with a train of a torsion spring 148 and with a friction clutch 149. Figure 46 is a cross-sectional view of two halves of worms 143 and 150 and the worm gear 147 with two trains including the torsion spring 148 with the friction clutch 149 and a torsion spring 151 with a friction clutch 152. As shown in Figure 24, the input shaft 114 drives worm gear 113. Output shaft 115 rotates with the rotor 112. Electrical power is supplied to the on/off clutch 118 or alternatively to an auxiliary motor. A brush commutation connection could be utilized for the inventive purposes described in this application. A control system (not shown) interrupts power between the source of electricity and the auxiliary motor or the on/off clutch. For the on/off clutch application with normal condition "on", the appearance of power changes the condition to "off".

For positive rotation of the input shaft 114, the clutch 118 has an "off" condition. Rotation of the shaft 114 in a positive direction with worm gear 113 rotating about its axis causes the worm 111 to rotate about the axis of worm gear 113 with rotor 112. This rotation is without relative movement between the worm 111 and worm gear 113. That is, the teeth of the worm gear 113 directly engage the thread on the worm 111, and there is no relative movement during this transmission. This rotation is provided by a normal force from the worm gear teeth against the thread on the worm. There is no relative movement, and thus the efficiency is maximum. This way, rotation of the output shaft 115 is achieved. This rotation is achieved if the teeth and threads are designed to be "self-locking" as described above. A worker of ordinary skill in the art would recognize how to design a self-locking gear set. For negative rotation of input shaft 114, clutch 118 has an "on" condition. Rotation of the shaft 114 also rotates gears 116, 117 and the worm 111. This rotation is provided such that the thread on the worm 111 avoids any forces from the teeth on worm gear 113, thus avoiding any transmission of rotation to the worm 111, and rotor 112. Even when the ratio of the gear train is more than the ratio of worm gear/worm, the clutch 118 permits sliding to prevent the gear train from crushing. Rotation from the input shaft 114 is not transferred to the output shaft 115.

It is also desirable to have some gap between the teeth on the worm gear 113 and the worm 111. The gap is taken up prior to any transmission of rotation, and it is desirable that the contact be initially taken up as a low torque load. These features are explained in more detail in the above parent application.

As an example, worm 111 as shown in Figures 25 and 26, rotates by transmission of rotation through flexible shaft 121. This design takes less space. The ratio between the worm 111 and worm gear 113 would require an auxiliary motor or gear train, turning the worm 111 to avoid interaction with the teeth on worm gear 113 that would be impractical when the input speed is very high. Most preferably, the ratio between worm and worm gear is less than 12. It is possible that only 2 teeth need to be utilized on the worm gear 113. As explained above, the transmission of power from the worm gear 113 to the worm 111 occurs without relative movement and is typically the case with the worm and worm gear combination. Rather, the teeth of the worm gear 113 are brought into contact with the thread on the worm 111, and the worm gear 113 is prevented from rotation about its own axis. A force is applied to the worm gear 113 which drives the worm 111 about the axis of the worm gear 113, thus imparting rotation to the rotor 112.

Since the worm and worm gears are not utilized as in standard gears to have interengaging teeth and threads, the material selected for the members is different than that which has been utilized in the past. In the past, the worm and worm gears have been formed of materials having low coefficients of friction and a lubricant is typically utilized. In this invention, lubricant would not be needed. Moreover, the worm and worm gear are made from a strong material such as steel . The shape of the teeth and threads and the worm and worm gears are designed to achieve a self-lock feature. In addition, a material that actually increases the friction may be placed on the teeth and threads. Again, it is a goal to achieve the self-locking property, rather than any smooth movement between the worm and the worm gear. The reduction of the number of teeth on the worm gear also reduces the inertia of the worm gear, thus increasing the speed at which the worm gear can shift between its oscillating inputs. Finally, rather than simply reducing the number of worm gear teeth, the thickness of the worm thread could be reduced to result in an acceptable gap. The gear train or pulley drive with on/off clutch or auxiliary motor will be of a relatively low torque. Its function is to turn the worm without any interaction relative to the teeth of the worm gear and to stop under overload even when the worm is fixed by the worm gear. Thus, a high torque motor or on/off clutch need not be utilized. For that reason, only a low amount of electrical energy is required to operate the on/off clutch or auxiliary motor.

The supply of electric energy to rotate the on/off clutch or the auxiliary motor leads to additional inconvenience. Besides, for many applications there is a need to change transferring torque or speed of rotation and change direction of the output shaft. For this purpose we use a differential which has 2 degrees of freedom. By taking off (freezing) one degree of freedom, it transforms the differential into a planetary transmission. Different examples of such designs are shown in Figure 27-Figure 33.

Figure 27 and Figure 30 describe transmissions for transferring positive/negative rotation of the input shaft 114 with different torque or disconnecting the output shaft 115 from the input shaft 114. The ratio depends on the number of teeth in gears 122 and 123.

Figures 28, 29 and 31 describe transmissions for changing the direction of rotation from the input shaft 114 with a different torque or disconnecting the output shaft 115 from the input shaft 114. The ratio depends on the number of teeth in gears 128 and 123.

Figures 32 and 33 describe transmissions for changing the direction of rotation with the same torque or disconnecting the output shaft 115 from the input shaft 114.

When adding the pair of worms 111 and 135, rotors

112 and 133 with the means (auxiliary motor 127 and auxiliary motor 137 or gear train with gear 116, gear 117, on/off clutch 118 and gear train with gear 140, gear 141, on/off clutch 142) and the worm gear 113 and the worm gear 136 with each of the worm gears being driven by an independent input shaft to a differential for connecting the worm gears with the members of the differential, we are able to change the ratio from the first number to the second number or to change the direction of rotation.

Figure 34 discloses a transmission for changing the direction of rotation from the shaft 114 to shafts 115 or 138 or disconnecting the output shaft 115 from the input shaft 114. When the worm gear 113 is held by the worm 111, then the shaft 138 has the direction of rotation of the input shaft 114. When worm gear 136 is held by worm 135, the shaft 115 has an opposite direction of rotation from the input shaft 114.

Figures 35-40 disclose the designs of a transmission with a ratio of 1 (one) for connecting the input shaft

114 with the output shaft 115, when the worm gear 136 is held by the worm 135. Also, these designs are used for changing the ratio between the input 114 and the output

115 when the worm gear 113 is held by the worm 111 or disconnecting the input shaft 114 from the output shaft

115 when the worm gear 113 and the worm gear 136 are free. Figures 35-37 are different from Figures 38-40 in the drive means used for rotating the worms 111 and 135.

By combination of the transmission devices described in Figures 24-40 we can make many different designs of transmissions. Examples of such kinds of designs are Figure 41 and Figure 42. Figure 41 is a combination of the device of Figure 24 with the device of Figure 33. Only rotor 113 is grounded. In Figure 42 the rotors 113 and 133 are grounded. But this combination has other properties. When the worm 135 holds the worm gear 136, the ratio between the input 114 and the output shaft 115 is 1 (one) . When the worm 111 holds the worm gear 113, the ratio between the input 114 and the output shaft 115 is -1 (minus one) .

When the enveloping worm has a large angle of envelop, assembling the worm with a gear becomes complicated. Using only half or less than half of a split enveloping worm along the axis of its rotation makes assembling more simple (Figure 43) . When congruent surfaces of the lands on the half worm and the teeth of the worm gear are sloped (Figure 44) so that there is normal free-wheeling of the worm upon rotation of the worm gear in one direction but there is locking action upon rotation of the worm gear in the other direction, it is not necessary to use complicated means with the gear train or auxiliary motor. In this case (Figure 45) half or less than half of a split worm 143 can be provided with means which include a train of a torsion spring 148 with a friction clutch 149 where the worm 143 is attached to the torsion spring 148 and the friction clutch 149 is attached to a rotor 144. Torsion spring 148 helps to remove clearance between the thread of the worm 143 and the tooth of a worm gear 147 after each change in direction of rotation of the input shaft 114. Figure 46 shows that each of the worms 143 and 150 and the worm gear 147 combinations described above can transmit very high torque loads.

All of the above described designs show that a transmission may be utilized to transmit the oscillating input on the shaft 114 into a single directional rotation on the output shaft 115 but also have more functions to compare with the prior art. It should be understood that in the embodiments of Figures 24-46, which generally illustrate an enveloping worm and enveloping worm gear, the worm and worm gear are preferably of the types disclosed with reference to Figures 1-23 including full and split enveloping worm and worm gear designs. All of the above-described designs show that a transmission device may be utilized to transmit the oscillating input on the shaft 114 into a unidirectional rotation on the output shaft 115 but also have more functions to compare with the prior art . For using the invention to regulate speed in a transmission, the present invention is based on the principal of differential systems. These systems have three members: an input, an output, and a control member. Various combinations of connecting these members with the worm gear results in different performances and characteristics. Input power goes from the input to the output of the differential. The control member is normally stationary under internal reactions. When the input of the differential is connected to a constant speed source of unidirectional mechanical energy, the output speed depends upon a speed of the control member of the differential. To provide motion to the control member, an auxiliary motor unlocks the worm gear by rotating the worm in a direction with the internal reactions on the worm (not against the direction of the internal reactions) . Unlocking motion of the worm gear under load does not require much power, compared to power transmitted from the input to the output of the differential. The low ratio of the enveloping worm and worm gear do not require much power from the auxiliary motor.

The new invention described above has some advantages. For transmitting oscillation motion, it provides the fast reverse of a movement of the output shaft by changing the direction of rotation by an auxiliary motor. It requires little or no lubrication between the working parts because a worm and a worm gear have relative motion only when the worm is unloaded and eliminated of backlash between the worm gear and the worm. For speed regulation in a variable speed transmission it allows lubrication between the working parts without losing self-locking (due to the self-locking geometry of the worm/worm gear transmission) that increases efficiency by reducing power to provide unlocking motion of the worm.

Several embodiments of the present invention have been disclosed. A worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention.

The invention being thus described, it will be obvious that the same may be varied in many ways . Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

CLAIMSWhat is claimed is:

1. A worm/worm gear transmission, comprising: an enveloping-type worm gear (16) with less than 24 teeth (14) ; and an enveloping worm (10) having at least one thread (12) that is engaged by at least one tooth (14) of said enveloping worm gear (16) .

2. The worm/worm gear transmission as recited in Claim 1, wherein said enveloping-type worm gear (16) has less than 12 teeth.

3. The worm/worm gear transmission as recited in Claim 1, wherein a tooth surface of said enveloping-type worm gear (16) generated by a profile of said enveloping thread (12) has an enveloping angle that is greater than 15 degrees for one revolution of said at least one thread.

4. The worm/worm gear transmission as recited in Claim 2, wherein a tooth surface of said enveloping-type worm gear (16) generated by a profile of said enveloping thread (12) has an enveloping angle greater than 30 degrees for one revolution of said at least one thread.

5. The worm/worm gear transmission as recited in Claim 1, wherein said enveloping-type worm gear (16) is engaged by at least one thread of a second enveloping worm

(10) located on an axis of rotation that is different from an axis of rotation for said enveloping worm (10) .

6. The worm/worm gear transmission as recited in Claim 3, wherein said enveloping worm is part of a split worm (50) .

7. The worm/worm gear transmission as recited in Claim 1, wherein said enveloping worm is connected to a drive shaft (56) supporting said worm only from one side.

8. The worm/worm gear transmission as recited in Claim 1, wherein said enveloping-type worm gear is connected to a drive shaft (46) supporting said enveloping-type worm gear only from one side.

9. The worm/worm gear transmission as recited in Claim 1, wherein said enveloping worm (84) is located in an off-center position with respect to said enveloping- type worm gear (80) .

10. A transmission device, comprising: a differential gear set having a first input member, a second input member (114) and an output member (115) ; an enveloping-type worm gear (113) connected to said first input member of said differential gear set, said enveloping-type worm gear (113) having less than 24 teeth; an enveloping worm (111) in meshing engagement with said enveloping-type worm gear (113) , said enveloping worm (111) and said enveloping-type worm gear (113) being self-locking against driving from said enveloping-type worm gear (113) ; and means (127) for rotating said enveloping worm (111) relative to said enveloping-type worm gear (113) to provide unlocking motion.

11. The transmission device according to Claim 10, wherein said differential gear set includes two sun gears

(122, 123) and a planetary carrier (126) for supporting at least one planet pinion (124) in meshing engagement with said sun gears (122, 123) .

12. The transmission device according to Claim 10, wherein said differential gear set includes a sun gear

(123), a planetary carrier (126) supporting at least one planet pinion (130) in meshing engagement with said sun gear (123), and a ring gear (128) in meshing engagement with said at least one planet pinion (130) .

13. The transmission device according to Claim 10, wherein said differential gear set is a bevel gear differential including a carrier (133) rotatably supporting a pair of pinion gears (131) in meshing engagement with said two side gears (129, 134) .

14. The transmission device according to Claim 10, wherein said enveloping worm is part of a split worm

(143) .

15. A worm/worm gear transmission, comprising: a worm gear (204) ; and a bodiless enveloping worm (200) having at least one thread (202) that is engaged by at least one tooth of said worm gear (204) .

16. The worm/worm gear transmission according to Claim 15, wherein said at least one thread (202) of said bodiless enveloping worm is connected at end portions thereof to a first and a second support member (206) .

17. The worm/worm gear transmission according to Claim 15, wherein said bodiless enveloping worm (200) includes at least two threads (202) which are each connected at opposite end portions thereof to a pair of support members (206) and further comprising an intermediate support member (208) extending between said at least two threads (202) intermediate said end portions.

18. The worm/ worm gear transmission according to Claim 15, wherein said bodiless enveloping worm (212) is part of a split worm.