WO1993004304A1

WO1993004304A1 - Lightweight high reduction ratio planetary gear assembly

Info

Publication number: WO1993004304A1
Application number: PCT/US1992/007000
Authority: WO
Inventors: Thomas L. Sbabo
Original assignee: United Technologies Corporation
Priority date: 1991-08-21
Filing date: 1992-08-21
Publication date: 1993-03-04

Abstract

A planetary gear reduction assembly is provided with a ring gear (16) and a sun gear (12) which are each adapted to be directly driven in opposite directions by a rotary input to slowly drive pinions (14). An initial split or sharing of torque, i.e. load sharing, is provided with a rotary input consisting of an input shaft (22) and bevel gear (26) which simultaneously drives gears (28) and (30) in opposite directions. Gears (28) and (30) are supplemental driving surfaces of the sun gear (12) and the ring gear (16) respectively, and are operatively engaged by driving surfaces of bevel gear (26). Gears (28) and (30) are integral to sun gear (12) and ring gear (16) respectively. Gears (28) and (30) can also be driven by a second input shaft (36) and bevel gear (34). Gear (28) is a flanged extension of sun gear (12) which drives pinions (14). Gear (30) is a flanged extension of ring gear (16) which also drives pinions (14). The sun gear (12) and ring gear (16) are caused to rotate in opposite directions about a concentric axis (38). This configuration provides high gear reduction. It also provides a high Ds/Dr (diameter of sun gear to diameter of ring gear) ratio for accommodating a large number of planetary pinions to share in load transfer. A further embodiment of the invention replaces ring gear (16), sun gear (12), and pinion gears (14) with friction roller gears.

Description

Lightweight High Reduction Ratio Planetary

Gear Assembly

Technical Field This invention relates to planetary reduction gears, and more particularly to a lightweight high reduction planetary reduction gear assembly.

Background Art

Planetary gear configurations have traditionally been used for rpm or angular velocity reduction from an input shaft to an output or second stage shaft. Planetary reduction gears are used extensively in helicopters since large rpm reduction is required to transfer power from a high rpm turbine engine shaft to a low rpm main rotor shaft. Traditional planetary gear assemblies are comprised of a sun gear, a ring gear, and planetary pinions. The planetary pinions are located^" between the ring and sun gears and are connected to a carrier member which equally spaces the pinion gears about the sun gear. A conventional planetary reduction gear configuration used in aircraft is disclosed in U.S. Patent No. 2,150,540 and a planetary reduction gear configuration having high load sharing is disclosed in U.S. Patent No. 3,062,073.

Typically, one of the three components of a planetary gear configuration is held fixed while the two remaining components serve as the drive and driven members. In most applications, the ring gear is held stationary and the sun gear is driven, which results in the planetary pinions being driven circumferen¬ tially around the sun gear at reduced rpm or angular velocity.

The magnitude of reduction of angular velocity, as well as the degree of load sharing and associated weight reduction, is greatly influenced by a number of geometric parameters. The diameter ratio of the sun gear to the ring gear (Ds/Dr) determines the reduction in angular velocity and the space available for planetary pinions. Generally, the larger this ratio (or closer to unity) , the smaller will be the angular velocity reduction and the larger will be the number of planetary pinions. Furthermore, the larger the number of planetary pinions the lower will be the individual tooth load. Reduced tooth load in turn reduces the necessary face width of an individual tooth. The smaller the face width, the lighter will be the overall planetary system weight.

In contemporary planetary drive assemblies of this type, high reduction ratios are achieved when the sun gear is small as compared with the ring gear (small Ds/Dr ratio) . The result of this arrangement is a large ring gear, a small sun gear, and only a few planetary pinions to provide load sharing. Perhaps only three planetary pinions, having a diameter extending from the circumference of the sun gear to that of the ring gear, will be capable of physically occupying the space therebetween without interference. While the rpm or angular velocity reduction will be relatively large, the tooth load will be high since only a small number of teeth (one on each pinion at any time) will share the load of the system. The high tooth load requires that the tooth face width be large to adequately transmit the load. A large tooth face width, in turn, substantially raises the weight of the planetary system since the collective weight of ring, sun, and pinion gears all having relatively large tooth face widths is substantially greater than that of similar gears having relatively small tooth face widths. Low load sharing thus results in a relatively heavy planetary gear assembly, which represents a significant drawback in many aerospace applications such as helicopter gear assemblies where weight is a primary concern. If the sun gear is nearly as large as the ring gear (Ds/Dr ratio approaching 1) , a large number (theoretically approaching an infinite number) of planetary pinions could be utilized thereby lowering individual tooth load by enabling more pinions to share in load transfer. Unfortunately, as the diameter of the sun gear approaches that of the ring gear, little angular velocity reduction is achieved (the reduction ratio approaches 2:1). Thus, in a conventional planetary gear reduction system,- low system weight through increased load sharing must be sacrificed in order to achieve high gear reduction ratios.

Disclosure of the Invention

An object of the present invention is to reduce the weight of a planetary reduction gear assembly.

Another object of the present invention is to increase the reduction ratio of a planetary reduction gear assembly. A further object of the invention is to reduce the noise associated with a planetary reduction gear assembly. According to the invention, a planetary reduction gear assembly has a sun gear of slightly smaller diameter than a ring gear, and both the sun and ring gears are adapted to be directly driven in opposite directions by a rotary input means to slowly drive many pinions, thereby achieving significant reduction of rpm or angular velocity and weight. In a further embodiment of the invention, the reduction gear assembly may be fabricated with friction roller gears instead of toothed gears, thereby achieving a substantial reduction in noise.

The invention affords the further benefit of providing the ability to reduce the size and manufacturing cost of the reduction gear assembly.

These and other objects, features and advantages of the present invention will become more apparent in light of the detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawing.

Brief Description of Drawing FIG. 1 is a diagrammatic plan view of a prior planetary reduction gear assembly.

FIG. 1A is a sectional side view of the planetary reduction gear assembly of FIG. 1, taken at line 1A-1A thereof. FIG. 2 is a partly broken away and partly sectional plan view of the planetary reduction gear assembly of the invention.

FIG. 2A is a sectional side view of the planetary reduction gear assembly of FIG. 2 taken along line 2A-2A thereof.

FIG. 2B is a sectional side view of the planetary reduction gear assembly similar to FIG. 2A but depicting the input shafts at an acute angle to that portion of the axis of the assembly which is above the imaginary point of intersection of the shafts and the axis.

FIG. 2C is a sectional side view of the planetary reduction gear assembly similar to FIGS. 2A and 2B but depicting the input shafts at an obtuse angle to that portion of the axis of the assembly which is above the imaginary point of intersection of the shafts and the axis.

FIG. 3 is a sectional side view of the planetary reduction gear assembly of the invention as configured with friction roller gears.

Best Mode for Carrying Out the Invention

Referring to FIGS. 1 and 1A, a prior planetary reduction gear assembly 110 consists of a sun gear 112, planetary pinions 114, and a ring gear 116. The sun gear 112 is positioned concentrically with the ring gear 116, and the planetary pinions 114 are located between the ring and sun gears. The pinions 114 are equiangularly spaced about sun gear 112 and mounted for rotation on respective axles 115 which are in turn collectively supported by a common carrier member 118. The ring gear 116 is held fixed or stationary while the sun gear 112 serves as the drive member and the pinions 114 and carrier member 116 serve as the driven members. As the sun gear 112 is driven in a clockwise angular direction, the pinions 114 each rotate on their axes in a counter-clockwise angular direction. As the pinions so rotate, they in turn rotate the carrier 118 in a clockwise angular direction that is slower than that of the sun gear 112. Input and output shafts 122 and 124 respectively are illustrated in FIG 1A as they interface with the planetary reduction gear assembly 110. The sun gear 112 is driven by an input shaft 122, and the carrier 118 drives output shaft 124 which, in the instance of a helicopter, is connected directly to the main rotor (not shown) .

Referring now to FIGS. 2 and 2A, the planetary reduction gear assembly 10 of the present invention is in most respects functionally similar or identical to gear assembly 110 of FIGS. 1 and 1A. However, in contrast to most planetary systems which utilize either the ring 16 or the sun 12 to drive the planetary pinions 14, the present invention provides for directly driving both the ring and sun gears 16 and 12 respectively, in opposite directions to slowly drive the pinions 14. This arrangement proves to be advantageous over other planetary gear arrangements because torque is split or shared initially between the ring 16 and sun 12, rather than being split subsequently through the use of secondary planetary stages as is done in some systems. The invention thus provides enhanced gear reduction and load sharing with a single planetary stage without the use of additional componentry, resulting in a simplified design which may both lower production costs and reduce weight relative to multi-stage gear reduction configurations. The invention accomplishes the initial split of torque with a rotary input means consisting of an input shaft 22 which has a bevel gear 26 and which simultaneously drives gears 28 and 30 in opposite directions. Gears 28 and 30 respectively are supplemental driving surfaces of the sun gear 12 and the ring gear 16 respectively, and are operatively engaged by driving surfaces of bevel gear 26. Gears 28 and 30 respectively are each integral with the sun 12 and ring 16 respectively. Gear 28 is a flanged extension of sun gear 12 which drives pinions 14.

Gear 30 is a flanged extension of ring gear 16 which also drives pinions 14. The sun gear 12 and ring gear 16 are caused to rotate in opposite directions about a concentric axis 38. Splitting the load of the system between the two gears 28 and 30 allows the bevel gear 26 to be sized smaller than if it were driving a single one of those gears. Thus, by simultaneously driving both gears 28 and 30, the bevel gear 26 accomplishes initial load sharing which serves to reduce system weight. The input shaft 22 may conveniently be an output shaft of a turbine engine (not shown) . Gears 28 and 30 can also be driven by a second input shaft 36 and bevel gear 34, which bevel gear also provides initial load sharing. The input shaft 36 may conveniently be an output shaft of a second turbine engine (not shown) which typically operates in synchronization with the first turbine engine which drives input shaft 22. It will be understood that input shafts 22 and 36 are normally mounted for rotation only about their own axes.

Referring now to FIG. 2A, the angle of each drive shaft 22 and 36 respectively, relative to the concentric axis 38, is 90 degrees. This has the effect of rotating both the sun gear 12 and the ring gear 16 at the same angular velocity, or rpm (revolutions per minute) because the effective pitch diameters of the gears 28 and 30 are the same.

However, because of the difference in pitch diameters of the sun and ring gears 12 and 16 respectively, the tangential velocities of those gears where they engage and drive the pinions 14, or pitch-line velocities, are not equivalent. The ring gear 16 having a greater diameter, has a higher pitch-line velocity and thereby drives the pinions 14 faster than does the sun gear 12.

In theory, if the angular velocity or rpm of the sun gear 12 were increased sufficiently to compensate for its reduced diameter, each planetary pinion 14 would rotate on its axis without advancing in its orbit about the sun gear 12. However, since the ring gear 16 drives the planetary pinions 14 somewhat faster (higher pitch-line velocity) than does the sun gear 12, the pinions 14 do traverse orbitally around the sun gear 12. The opposite angular rotation of the ring 16 and sun 12 causes the pinions 14 to rotate on their axes at a high angular velocity or rpm, yet the difference in tangential or pitch-line velocities generated by the difference in diameters of the two gears 12 and 16 results in rotation of carrier 18 at an angular velocity that is substantially less than that of the input drive shafts 22 and 36. The output shaft 24 is fixed to the slowly rotating carrier 18, which results in a large reduction in angular velocity from the high rpm input shaft 22 to the low rpm output shaft 24.

Alternatively, as depicted in FIGS. 2B and 2C, the angle of the input shafts 22 and 36 relative to the concentric axis 38 of the ring gear 16 and sun gear 12, can be altered to further adjust the reduction ratio, while maintaining load sharing of the bevel gears 26 and 36 with the ring gear 16 and sun gear 12. Referring first to FIG. 2B, the angle of each drive shaft 22 and 36, relative to that portion of the concentric axis 38 which is above the imaginary point of intersection of each respective shaft and the axis 38, is less than 90 degrees. Thus, in this configuration, the ring gear 16 is rotated at a slightly higher angular velocity than that of the sun gear 12 because the effective pitch diameter of gear 30' which drives ring gear 16 is less than the effective pitch diameter of gear 28' which drives sun gear 12. This has the effect of slightly decreasing the effective reduction of the planetary reduction system.

In FIG. 2C, the angle of each drive shaft 22 and 36 respectively, relative to that portion of the concentric axis 38 which is above the imaginary point of intersection of each respective shaft and the axis 38, is greater than 90 degrees. Thus, in this configuration, the sun gear 12 is rotated at a slightly higher angular velocity than that of the ring gear 16 because the effective pitch diameter of gear 28' ' which drives sun gear 12 is less than the effective pitch diameter of gear 30" which drives ring gear 12. This has the effect of increasing the effective reduction of the planetary reduction system. Referring back to FIG. 2, the invention, in addition to providing high gear reduction, provides a high (approaching unity) Ds/Dr (diameter of sun gear to diameter of ring gear) ratio, thereby accommodating a large number of planetary pinions (only eight are shown, but considerably more are possible) . Hence, a large number of planetary pinions 14 share in load transfer. Because the portion of the load on each pinion tooth is relatively reduced, the gear tooth face width may be reduced, thereby reducing the weight of the pinion 14. Similar reductions in gear tooth face widths are thus also afforded to the sun gear 12 and ring gear 16 such that their weights are also reduced. This permits the weight of the system to be reduced since the collective weight of the gear components of a high load sharing planetary gear reduction assembly is substantially less than that of an assembly with low load sharing.

As a result, the invention achieves a substantial increase in gear reduction while maintaining high load sharing for weight reduction. In a typical applica¬ tion such as a small helicopter, the invention, utilizing essentially the same size planetary gear componentry as is in current use, could achieve a reduction ratio of from 6:1 to 9:1 which represents a 28% to 290% improvement in reduction ratio as compared to reduction ratios achieved with conventional planetary gear configurations in similar applications which range from approximately 2.3:1 to 4.7:1.

Theoretically, the improvement could be even greater. In helicopter applications, the invention has the potential to provide substantially greater angular velocity reduction as well as greater load sharing, with the major limitation being the angular velocity at which conventional pinion bearings can reliably operate, since the greater the reduction ratio, the greater the angular velocity of pinions 14 on their axes. Improvements in bearing technology could significantly increase the reduction ratio available with the invention since the reduction ratio theoretically approaches infinity as the Ds/Dr ratio approaches 1. Current bearing technology however may still permit significantly higher gear reductions in other applications which utilize slower input speeds for even slower output speeds.

Referring now to FIG. 3, a further embodiment of the invention replaces the toothed ring gear 16, the toothed sun gear 12, and the toothed pinion gears 14 with friction roller gears. Sun 12', pinions 14', and ring 16' all have frictional surfaces in lieu of gear teeth which transfer system load between them. Friction rollers have several potential advantages, including the further reduction of weight through enhanced load sharing, the reduction of expense due to the simplification of the manufacture of components, and the substantial reduction of gearbox noise which is a major source of noise generated by a helicopter. Friction rollers could not be used in conventional helicopter applications due to the large face widths (and consequently the large size and weight) that would be required of the pinion rollers in order to adequately transfer the load generated by a conventional planetary gear reduction system with a conventional Ds/Dr ratio. However, since the invention provides high reduction ratios at relatively large Ds/Dr ratios, a large number of friction roller pinions each having a very small diameter could be used in conjunction with the invention so that the load transferred by each roller would be low enough to allow the use of rollers each having relatively small roller face widths. Again, as with the first embodiment of the invention, a limiting factor is the capacity of the pinion bearings. It should be understood that the sun and ring could each be driven by separate input means and still remain within the scope of the invention.

It should also be understood that the invention may be configured in other manners which serve to increase or decrease the rpm of either the sun gear or the ring gear relative to the other, and still remain within the scope of the invention.

Although the invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. A planetary reduction gear assembly for transferring torque from a rotary input means to a rotary output means comprising: a sun gear; a ring gear operatively disposed about said sun gear in concentric relation therewith; a plurality of pinions each disposed between and in mutual engagement with said sun gear and said ring gear, each said pinion being disposed to rotate on its respective axis; and a pinion carrier disposed to rotate concentrically with said sun gear and said ring gear, said pinions being rotatably mounted to and carried by said carrier; characterized by: said sun gear and said ring gear being adapted to be directly engaged by and driven in respectively opposite directions by said rotary input means.

2. The planetary reduction gear assembly of claim 1 further characterized by: said sun gear and said ring gear each including supplemental drive surfaces adapted to directly engage said rotary input means.

3. The planetary reduction gear assembly of claim 2 further characterized in that: each said supplemental drive surface has a respective pitch diameter relative to the input means for driving said sun gear and said ring gear at equivalent angular velocities.

4. The planetary reduction gear assembly of claim 2 further characterized in that: said supplemental drive surface of said sun gear has a smaller pitch diameter than said supplemental drive surface of said ring gear, each relative to said input means, to drive said sun gear at a higher angular velocity than that of said ring gear to increase the reduction ratio of said gear reduction assembly relative to an assembly in which both said sun and said ring gear supplemental drive surfaces have equivalent pitch diameters.

5. The planetary reduction gear assembly of claim 2 further characterized in that: said supplemental drive surface of said sun gear has a larger pitch diameter than said supplemental drive surface of said ring gear,- each relative to said input means, to drive said sun gear at a lower angular velocity than that of said ring gear to decrease the reduction ratio of said gear reduction assembly relative to an assembly in which both said sun and said ring gear supplemental drive surfaces have equivalent pitch diameters.

6. The planetary reduction gear assembly of claim 2 as further characterized by: said sun, pinion, and ring gears consisting of friction roller gears.

7. The planetary reduction gear assembly of claim 2 further characterized in that: said supplemental drive surfaces are tapered for direct engagement by bevel gear rotary input means.

8. The planetary reduction gear assembly of claim 7 further characterized by: said sun, pinion, and ring gears consisting of friction roller gears.

9. The planetary reduction gear assembly of claim 1 further characterized by: said sun, pinion, and ring gears consisting of friction roller gears.

10. A method for transferring torque from a rotary input means to a rotary output means via a planetary reduction gear assembly which comprises: a sun gear; a ring gear operatively disposed about said sun gear in concentric relation therewith; a plurality of pinions each disposed between and in mutual engagement with said sun gear and said ring gear, each said pinion being disposed to rotate on its respective axis; and a pinion carrier disposed to rotate concentrically with said sun gear and said ring gear, said pinions being rotatably mounted to and carried by said carrier; characterized by the steps of: mounting said sun gear and said ring gear for rota¬ tion on their respective axes; and directly engag- ing and driving said ring gear and said sun gear in opposite directions via said rotary input means.