WO2011064629A1

WO2011064629A1 - Means of improving gear tooth load distribution

Info

Publication number: WO2011064629A1
Application number: PCT/IB2010/001672
Authority: WO
Inventors: Robert Budny; Ehren W. Van Schmus; Carl G. Wood; Brad D. Banwarth; Jesse M. Hanson
Original assignee: Clipper Windpower, Inc.
Priority date: 2009-11-28
Filing date: 2010-07-07
Publication date: 2011-06-03

Abstract

The invention relates to a drive shaft device for a transmission unit. The drive shaft device comprises a shaft unit (12; 112) of a flexible coupling type, an end of which is equipped with a pinion (14) for engagement with a gear wheel; and a sleeve element (16) which co-axially extends over an essential length of the shaft unit (12) and is spaced radially from the shaft unit (12; 112). The pinion (14) of the shaft unit (12; 112) protrudes out of the sleeve element (16), whereas the other end of the shaft unit (12; 112) is fastened to the sleeve element (16) by means of a spline joint connection.

Description

MEANS OF IMPROVING GEAR TOOTH LOAD DISTRIBUTION

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates in general to gear systems and, more particularly, to an improved drive shaft device for a

transmission unit, for example a helical gear system.

Description of the Prior Art

When a pair of gears is in mesh, the axes of gears must be parallel within very close tolerance. If they are not, the gear tooth load will not be evenly distributed across the tooth.

Current practice is to take great care to ensure close alignment between gear axes, and to make parts very rigid to limit

deflections. Alternatively, flexible couplings are employed, which are expensive, wear out, and require large envelopes.

An epicyclic configuration or arrangement consists of a ring of planet gears mounted on a planet carrier and meshing with a sun gear on the inside and an annulus gear on the outside. The sun gear and the planet gears are external gears and the annulus is an internal gear as its teeth are on the inside. Usually either the annulus or planet carrier is held fixed, but the gear ratio is larger if the annulus is fixed.

US 7,069,802 B2 describes an epicyclic gear assembly with a first stage double helix pinions and second stage helical gears (intermediate assembly) which are mounted on axially non- locating bearings. In the second stage, single helix output pinions engage adjacent second stage helical gears and are not constrained by bearings but are free to move radially. This results in a floating system without using a coupling to equalize thrust loads. The drawback of this system is that the gear timing and alignment of the single helix output pinions must be maintained in order to maintain gear mesh. Stiffness of the flexible coupling must be within a certain range in order for the float to accommodate deflections and misalignment of the gear system.

According to an example relating to the general field of the invention, a drive shaft or input shaft comprises at least at one end a pinion and interconnects two gears. The pinion is free to pivot to a mesh position that equalizes the tooth loads on two gear meshes which are driving it from opposite (180°) sides. That pivot function creates a small angle on the pinion axis, which in turn causes mal-distribution of contact across the mesh face. For small pivot angles, the teeth are crowned and this error is within acceptable design limits. However, for large offsets, the pivot angle is too large for crown compensation causing load distribution variation that exceeds acceptable design limits. It is an object of the present invention to provide a drive shaft device having an added degree of freedom on the prior output pinion, which permits the gear tooth forces to align the pinion body in multiple planes, to thereby obtain an improved tooth load distribution in terms of improved Kf factors with varying levels of mesh displacement.

SUMMARY OF THE INVENTION

The object of the invention is solved by a drive shaft device for a transmission unit, comprising a shaft unit of a flexible coupling type, an end of which is equipped with a pinion for engagement with a gear wheel, and a sleeve element which co- axially extends over an essential length of the shaft unit and is spaced radially from the shaft unit. The pinion of the shaft unit protrudes out of the sleeve element, whereas the other end of the shaft unit is fastened to the sleeve element by means of a spline joint connection. According to a preferred embodiment of the present invention, the shaft unit comprises a shaft extension one end of which is fastened to the sleeve element, and a shaft element including the pinion. In case of such a two-piece shaft unit, it is preferred that the shaft extension and the shaft element are connected via a spline joint interface.

The spline joint interface may be defined or constituted by a female spline formed on an inner circumferential surface of the shaft extension, and a male spline formed on an outer

circumferential surface of the shaft element. Alternatively, the spline joint interface may be defined by a male spline formed on an outer circumferential surface of the shaft extension, and a female spline formed on an inner circumferential surface of the shaft element. Such a spline joint or splined interface

comprises the benefit that it provides an equally distributed load along the sides of the spline teeth, wherein this shared load provides a longer fatigue life. According to a further embodiment of the inventive drive shaft device, the spline joint interface may be a crowned spline interface. In this respect, the end faces of the shaft extension and shaft element each comprise respective crowned or spherical thrust surfaces.

In another embodiment of the inventive drive shaft device, the sleeve element may be a gear wheel support sleeve which at one end is anchored in and cantilevered from a carrier element and which forms part of or carries a bearing device that supports a planet pinion of a planet gear stage.

According to another aspect of the present invention, the end of the shaft unit, connected to the sleeve element comprises a male spline formed on an outer surface of the shaft unit. In order to keep the existing lube delivery system of the drive shaft device, the shaft element or shaft unit may include a side-sealing piston ring seal for retaining a lubricating fluid. The inventive drive shaft device can be part of a multi-stage gearing apparatus or an electric power-generating device that converts fluid flow of wind or water to electricity. According to an embodiment of the invention, the drive shaft device may connect a torque-reducing gearbox or stage with a generator unit. Alternatively, the drive shaft unit may connect a torque- dividing gearbox or stage with a torque-reducing gearbox or stage .

The object of the invention is alternatively solved by an epicyclic gear unit. The epicyclic gear unit comprises a planet gear stage wherein at least one planet gear is rotatably

supported on a planet carrier. The planet carrier has a shaft of a flexible coupling type, and a sleeve, on which the planet gear is mounted. The shaft of the flexible coupling type has a second spline joint that allows an axis re-alignment of a short

separate pinion. The shaft of the flexible coupling type further comprises a drive shaft having a male spline at a proximate end and a female spline at a distal end for mating with the short pinion.

In accordance with an aspect of the invention, the short pinion of the epicyclic gear unit includes a side-sealing piston ring seal for retaining a lubricating fluid. The lubrication of components is designed to keep rotating components fully

lubricated by utilizing the current pressure lube system. No changes to the existing lube delivery system are contemplated. With the aid of the invention, the design does not require any significant technical changes and stresses are in the same general range as existing practices.

Summarizing the above, the invention has the advantage that the existing pivot function of a shaft, is retained, so as to retain equalized load distribution between the two meshes, but the pinion axis is allowed to counter pivot utilizing tooth forces, which strive for equilibrium. The invention employs a second crown spline joint that has the same general dimensions as the system described in the second stage of US 7,069,802 B2 but allows an axis re-alignment of a short separate pinion fixed to the end of a flexible coupling drive shaft.

The invention allows for greater initial misalignment, which allows for increased manufacturing tolerances and reduced costs. The invention also accommodates operating deflections, allowing for lighter weight construction, which is less expensive. The designs are also very compact. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to the drawings in which:

FIGURE 1 is a diagram of a drive shaft device according to a first embodiment of the invention;

FIGURE 2 is a cutaway perspective drawing of a drive shaft device according to a second embodiment of the invention; FIGURE 3 is a diagram of pinion offset in the Z axis, resulting in sideways reaction;

FIGURE 4 is a diagram of gear forces on the drive shaft device of the flexible coupling type resulting in parallel deflection;

FIGURE 5 is a diagram showing the mesh forces changed due to an external force ;

FIGURE 6 is a diagram illustrating the pinion moment due to sideway forces; FIGURE 7 is a diagram illustrating the pinion restoring moment due to tooth forces Fbl and Fb2;

FIGURE 8 is a chart showing the influence of the tooth load distribution factor Kf in respect to mesh restoring moment;

FIGURE 9 is a chart showing a close-up with the influence of 0,5mm pinion offset; FIGURE 10 is chart showing the influence of the tooth load distribution factor Kf in respect of mesh restoring moment, with reduced crowning;

FIGURE 11 is cutaway exploded diagram of the drive shaft device according to the second embodiment of the invention shown in FIGURE 2;

FIGURE 12 is a perspective view of the drive shaft device according to the second embodiment of the invention; and

FIGURE 13 is a further perspective view of the drive shaft device according to the second embodiment of the invention.

In these figures, the same reference numerals refer to similar elements in the drawings. It should be understood that the sizes of the different components in the figures may not be to scale, or in exact proportion, and are shown for visual clarity and for the purpose of explanation. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description relates to concepts for an added degree of freedom on a pinion which permits gear tooth forces to align a pinion body in multiple planes. The intent is to obtain improved tooth load distribution factors Kf with varying levels of mesh displacement. FIGURE 1 shows a drive shaft device 10, in particular for a gear system or transmission unit of a wind turbine, according to a first embodiment of the invention. The drive shaft device 10 comprises a long slender shaft unit 12, wherein a first end of the shaft unit 12 is equipped with a pinion 14 for engagement with a gear wheel (not shown) . The drive shaft device 10

comprises further a sleeve element 16 which co-axially extends over an essential length of the shaft unit 12 and is spaced radially from the shaft unit 12. Thus, a gap 20 is formed between the sleeve element 16 and the one-piece shaft unit 12. The pinion 14 formed at one end of the shaft unit 12 protrudes out of the sleeve element 16. The other or second end of the shaft unit 12 is fastened to the sleeve element 16 by means of a spline joint connection. For fastening purpose, a portion of the second end of the shaft unit 12 comprises a male spline 18 formed on its outer circumferential surface, whereas the sleeve element 16 comprises a female spline (not shown in FIGURE 1) formed on its inner circumferential surface and mating with the male spline 18 of the shaft unit 12.

The long slender shaft unit 12 is relatively compliant in bending. Accordingly, the compliance of the shaft unit 12 reduces the magnitude of the moment that is required to bend the shaft unit 12 for a given displacement (i.e. variance from parallelism between axes) . The reduction in moment causes a commensurate reduction in the non-uniformity of the load.

FIGURE 2 illustrates a cutaway perspective drawing of a drive shaft device 100 according to a second embodiment of the

invention. The drive shaft device 100 comprises the same

features compared with the first embodiment shown in FIGURE 1 with the exception of the feature of the one-piece shaft unit 12. Instead of that, the drive shaft device 100 comprises a two- piece shaft unit 112, wherein the same reference numerals refer to similar elements in FIGURES 1 and 2 so that a detailed description of such features is omitted. The two-piece shaft unit 112 comprises a shaft extension 114 one end of which is fastened to the sleeve element 16, and a shaft element 116 including the pinion 14. The length of the shaft element 116 is relatively short compared with the length of the shaft extension 114. In order to transmit torque via the two-piece shaft unit 112, the shaft extension 114 and the shaft element 116 are connected via a spline joint interface. As can be seen from FIGURE 2, the spline joint interface is defined by a female spline formed on an inner circumferential surface of the shaft extension 114, and a male spline formed on an outer

circumferential surface of the shaft element 116. Alternatively, the spline joint interface may be defined by a male spline formed on an outer circumferential surface of the shaft

extension 114, and a female spline formed on an inner

circumferential surface of the shaft element 116. Accordingly, dual splines are provided at the ends of each element (shaft extension 114 and shaft element 116) that is secured.

Further, with respect to FIGURE 2, a bearing device 118 is arranged around the sleeve element 16. According to such an arrangement, the bearing device 118 may support or carry the drive shaft units 10 and 100 shown in FIGURES 1 and 2 in a rotatable manner. In this case, the drive shaft unit 10 or 100 is driven from opposite (180°) sides, i.e. at both of its ends. On the other hand, the sleeve element 16 may be a gear wheel support sleeve which at one end is anchored in and cantilevered from a carrier plate of a planet gear stage (not shown) , so that the sleeve element 16 may form part of or may carry the bearing device 118 that may support a planet pinion of the planet gear stage. In this case, the sleeve element 16 is united to the carrier plate and carries the bearing device 118 which in turn supports the planet pinion. The bearing device 118 my take the form of a double row tapered roller bearing. According to the invention, a cantilevered support for a highspeed pinion 14 comprises an outer sleeve element 16 concentric with a gear-mounting pin or shaft unit 12 or 112. The mounting pin or shaft unit 12, 112 deflects in such a manner that the outside of the sleeve element 16 remains parallel to the system axis. The shaft of a flexible coupling type unit 12, 112

includes a drive shaft or shaft extension 114 that is secured to a wall or other member, thus cantilevering the inner pin or shaft unit 112 from the wall or other member. The sleeve 16 is cantilevered from the opposite end of the inner pin or shaft unit 112 and extends back over the inner pin, thus providing a double cantilever. Dual splines are provided at the ends of each element that is secured. The drive shaft spline is press-fitted into the back wall and the short pinion spline is press-fitted into the opposing end of the drive shaft. The spline is a series of ridges on the driveshaft, which mesh with and transfer torque, thereby maintaining the correspondence with the mating piece. The pinion gear mounted on the short shaft or shaft element 116 uses a male spline on the short shaft that matches a female spline on the cantilevered end of the drive shaft or shaft extension 114. Due to the upwind spherical gearing and a "pushing" load, there will be a sideways force created by any offset in the axis. The mesh forces and reactions as well as spline performance are examined in the following paragraphs. In FIGURE 3 the sideways force of concern is defined and later that function is quantified and the risk to de-stabilizing or changing load distribution in the gear meshes is examined.

With respect to mesh forces, pinion or shaft unit 12, 112 is driven from two sides at 180°, i.e. the shaft unit 12, 112 with the pinion is driven at both of its ends . The force vectors are depicted in FIGURE 4. In this arrangement the thrust loads cancel any over turning moment, thrust loads are additive and radial tooth loads also cancel . In FIGURE 4 Wt is the tangential load, Wr is the radial load and Wa is the axial (thrust) load. The sideways force Rz is determined by the degree of offset δ and length LI and thrust force Fx. Fx is determined for a given torque :

Fx = —■ tan( )

rp

where :

Rating 9549 2500 9549

Q -- = 5868,4 Nm

eff 4 · rpm 0,9

Ψ helix = 23,3976 degrees

rp pitch radius = 0,53313

5868,4

Fx 0,432689 = 47,628 N

0,053313 and:

Fx · δ _^

Rz where :

LI

δ -- offset = 0,5 mm

LI = length of link (shaft) 0,420 mm

47,628 · 0,5

Rz = = 56,7 N

420 This force is translated to the pinion via the spline extension which creates a moment on it . As seen in FIGURE , the tooth forces are balanced except for torque Mx and thrust Fx which are reacted by the generator flux (Rx) and the support structure (Ra) respectively. The side force Rz creates unbalance in the tooth force system as seen in FIGURE 5. Note that an asymmetric distribution of the tooth forces across the tooth face is created, wherein crowning is ignored here for simplicity. As can be seen from FIGURE 5, mesh forces are changed due to an

external force.

The asymmetrical tooth loads create a counter moment to balance the sideways force Rz and in so doing introducing a shift in the mesh load distribution factor Kf . The mesh restoring forces and their effect on load distribution Kf can be simulated by a software program called LVR. The program LVR provides software tools for dimensioning and

recalculation of load distributions in spur gears,, helical gears and planetary gears. By means of the software program LVR, mesh restoring forces and their effect on the load distribution Kf can be simulated. For this purpose, a model is generated

comprising a virtual bearing on each side of the pinion and external forces are introduced to have resulting reactions on each bearing cancelled to zero. When misalignment is introduced to the model, the program reports the changed bearing reactions which now represent only the forces due to non-uniform load distribution. This complex reaction is influenced by crowning and tooth deflections.

With the aid of the software program LVR, the interaction of gear tooth misalignment, resulting Kf factor and the resulting bearing reactions can be investigated. The software program LVR calculates new bearing reactions created as a result of

asymmetrical tooth loads when a tooth distribution error is introduced. In the mesh, if the pinion is free, these are the restoring forces that cause the pinion to want to. return to the position where all forces are balanced. Converting - the sideways force Rz to a moment to the pinion, the sideways force Rz is applied at a spline center and multiplied by the short pinion length L2. This yields the moment My (in Nm) on the short pinion axis. Likewise, the bearing reaction forces determined by the software program LVR can be changed to get the counter moment due to asymmetrical tooth forces. This exercise is seen in FIGURE 6 showing the pinion moment My due to the sideways force Rz . From the above it follows that:

My = Rz · L2 = 0,105 -56,7 = 8,51 Nm

The pinion restoring moment Mry due to tooth forces Fbl and Fb2 is depicted in FIGURE 7. From the above it follows that: Mry = Fbl · 1 / 2 Lw + Fb2 · 1/2 Lw

The reaction moment from the teeth is quite large and varies with tooth misalignment. These relationships based on current pinion design (crown level) are illustrated in the graph of FIGURE 8, which is a chart of the influence of Kf in respect of mesh restoring moment.

In the close-up shown in FIGURE 9, the influence of a 0,5 mm pinion offset together with the forcing or pinion moment My of 8,51 Nm is plotted to see what change in Kf is needed to

generate that counter moment.

As seen in FIGURE 9, the thrust force created sideways force Rz will not significantly influence the mesh, changing Kf from 1,36% to 1,38% or about 1,5%. This indicates a very effective solution where the sideways force Rz created by the pinion offset is very small compared to the tooth forces seeking uniform mesh load distribution. This implies that less crowning is needed whereas even stronger restoring moments are generated and the overall tooth stresses are reduced to levels of the current or basis design (i.e., a design with out spline joint connection or interface) even when there is no pinion offset. This is seen in the graph of FIGURE 10, which shows the

influence of Kf in respect to mesh restoring moment, with reduced crown.

The results of this case is to lower best case stress by about 14% and increase the restoring moment by the same amount. As expected, the best result is improved but with the price that the design is more sensitive to misalignment and that the design peaks out at a higher Kf factor for the maximum mesh

misalignment. Considering the extra degree of freedom, this misalignment is unlikely to occur, thus the design has the option to increase design margin and thus the life of the gear set. Splines are rated based on the work of Dale W. Dudley (Handbook of Practical Gear Design) for flexible spline application. Based on continuous offset of 0,5m, and including the combined load share and dynamic factor of 1,12 plus a design margin of 1,25 (application factor) the spline life for both ends- is adequate.

The drive shaft device 10, 100, to equal the current conditions, requires a surface hardness of 58 Rc minimum. Applied to the pinion 14 of the shaft unit 12, 112, there is an increased life in that joint due to both surfaces being at 58 Rc or greater vs. the downwind spline which has the spindle surface at 53 Rc minimum. A general view of the drive shaft device 100 according to the second embodiment of the invention is shown in FIGURE 11, FIGURE 12 and FIGURE 13. FIGURE 11 shows an exploded perspective view of the drive shaft device 100 comprising the two-piece shaft unit 112 and the sleeve element 16. The sleeve element 16 extends over an essential length of the shaft unit 112 and is spaced radially therefrom. The two-piece shaft unit 112 includes the shaft extension 114 and the shaft element 116 with the pinion 14. A first end of the shaft extension 114 is connected to the sleeve element 16 via a male spline 18 formed on an outer surface of the shaft extension 114. A second end of the shaft extension, opposite to the first end of the shaft extension 114, comprises a sleeve-type opening or receiving section 124. The receiving section 124 comprises a female spline 126 formed on the inner surface of the receiving section 124. The shaft element 116 with the pinion 14 comprises a male spline 128 formed on the outer surface of the shaft element 116 and mating with the female spline 126 of the shaft extension 114. The female spline 126 and the male spline 128 constitute a splint joint interface fastening the shaft extension 114 to the shaft element 116, wherein the pinion 14 formed at one end of the shaft unit 112 protrudes out of the sleeve element 16. Thus, dual splines are provided at the ends of each element shaft extension 114 and shaft element 116, respectively. As can be seen from FIGURE 11 and 13, the spline joint interface is a crowned spline interface defined in that the end faces of the shaft extension 114 and shaft element 116 comprise respective crowned or spherical thrust surfaces 130 and 132. Accordingly, the drive shaft unit 100 according to the second embodiment of the invention comprises a short shaft element 116 with a crowned spline interface to the shaft extension 114, allowing the drive shaft unit 100 to maintain parallelism. Further, as can be seen from FIGURES 11, 12 and 13, the drive shaft unit 100 includes a split steel reverse thrust retainer 120 and a snap or retaining ring 134 for engagement with the sleeve element 16.

In case that the invention is embodied in a planetary gear stage, a cantilevered support for high-speed pinion 14 contains an outer sleeve element 16 concentric with a gear-mounting pin 112. The mounting pin 112 deflects in a manner that the outside of the sleeve 16 remains parallel to the system axis. Such a shaft of the flexible coupling type 112 includes drive shaft 114 that is secured to a wall or other member by a spline 18, thus cantilevering the inner pin 116 from a wall or other member. The sleeve 16 is cantilevered from the opposite end of the inner pin 116 and extends back over the inner pin 116 , thus providing a double cantilever. Dual splines are provided at the ends of each element that is secured. The drive shaft spline 18 is press- fitted into the back wall and the short pinion spline 116 is press-fitted into the female end 126 of the drive shaft 114. The spline 18 is a series of ridges on the driveshaft 112, which mesh with and transfer torque, thereby maintaining the

correspondence with the mating piece. The pinion gear 14 mounted on the short shaft 116 uses a male spline on the short shaft that matches a female spline 15 on the cantilevered end of the drive shaft 16. According to the invention, the described drive shaft device 10 or 100 may be part of a drivetrain disclosed in US 7,069,802 B2. With respect to the drivetrain disclosed in US 7,069,802 B2 , the drive shaft device is a high speed pinion and connects intermediate gear(s) being a or torque-reducing stage with a generator unit. The lubrication system is designed to keep the spline joint connection and spline joint interface fully lubricated and flush out wear debris to prevent secondary abrasive wear. Current field experience with the lubrication system is favourable. A lubrication fluid is supplied through an opening in the shell of the sleeve element 16 within the gap between the sleeve element 16 and the drive shaft unit 10, 100 and flows around the one- piece or two-piece shaft unit 12 or 112. A bore is formed centrally within the shaft unit 12 or shaft extension 114 and shaft element 116 of the shaft unit 112 and serves for discharge of the lubrication fluid. To retain this system, a side-sealing piston ring seal 136 is used. This is a hook-type iron piston ring 136, a commercially available product. The side-sealing piston ring seal 136 replaces a polymer seal currently used, which is probably not as wear-resistant as the iron piston ring seal. These polymer seals have long been used in power-shift applications with excellent success. The hook-type side-sealing piston ring seal 136 has the advantage of simple installation without a requirement to compress it during installation, and is held in place by a flexible retainer 22.

The double spline high-speed pinion 14 will substantially alleviate the current variation in Kf factor due to pinion offset. It can be designed with substantial range and will fully respond to any offset within the design range. Load distribution variation is influenced by the degree of pinion offset and also by friction and dynamic factors, but these are predicted to be of a low order. A design starting point of +/- 1.0 mm of offset range built in to the internal clearance is recommended. A lubrication will keep rotating components fully lubricated by utilizing a pressure lube system. The extra degree of freedom permits a reduced crown resulting in an improved design margin compared to the PCT/IB2009/000041 design. Summarizing the above, the present invention discloses three means for reducing the sensitivity of the gears in mesh to poor load distribution due to axis misalignment. These three means of improving gear tooth load distribution are as follows:

1. A gear with a long slender shaft that is relatively compliant in bending. The compliance of the shaft reduces the magnitude of the moment that is required to bend the shaft for a given displacement (i.e. variance from

parallelism between axes) . The reduction in moment causes a commensurate reduction in the non-uniformity of the load.

2. A gear with a crowned internal spline connection to a shaft. The splined connection allows the axis of the gear to maintain parallelism.

3. A gear with short shaft with a crowned spline interface to a shaft extension, allowing the gear to maintain

parallelism.

These means according to the present invention allow for greater initial misalignment, which allows for increased manufacturing tolerances and reduced costs. They also accommodate operating deflections, allowing for lighter weight construction, which is less expensive. The designs are also very compact.

According to a further aspect of the present invention, in an epicyclical gear unit, said gear unit comprises a planet gear stage wherein at least one planet gear is supported on a planet carrier. Said planet carrier has a shaft, and a sleeve, on which the planet gear is mounted. Said shaft has a second spline joint that allows an axis re-alignment of a short separate pinion. According to the further aspect of the present invention, said shaft comprises a drive shaft having a male spline at a proximate end and a female spline at a distal end for mating with said short pinion.

Furthermore, according to the further aspect of the present invention, said short pinion includes a side-sealing piston ring seal for retaining a lubricating fluid.

The principles, preferred embodiments and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive.

Variations and changes may be made by others, and equivalents employed, without departing from thee spirit and scope of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.

Claims

1. A drive shaft device for a transmission unit,

comprising:

a shaft unit (12; 112) of a flexible coupling type, an end of which is equipped with a pinion (14) for engagement with a gear wheel; and

a sleeve element (16) which co-axially extends over an essential length of the shaft unit (12) and is spaced radially from the shaft unit (12; 112);

wherein the pinion (14) of the shaft unit (12; 112) protrudes out of the sleeve element (16) , whereas the other end of the shaft unit (12; 112) is fastened to the sleeve element (16) by means of a spline joint connection.

2. The drive shaft device according to claim 1, wherein the shaft unit (112) comprises a shaft extension (114) one end of which is fastened to the sleeve element (16) , and a shaft element (116) including the pinion (14) .

3. The drive shaft device according to claim 2, wherein the shaft extension (114) and the shaft element (116) are connected via a spline joint interface.

4. The drive shaft device according to claim 3, wherein the spline joint interface is defined by a female spline (126) formed on an inner circumferential surface of the shaft extension (114) , and a male spline (128) formed on an outer circumferential surface of the shaft element (116) .

5. The drive shaft device according to claim 3, wherein the spline joint interface is defined by a male spline formed on an outer circumferential surface of the shaft extension (114), and a female spline formed on an inner circumferential surface of the shaft element (116) .

6. The drive shaft device according to one of the claims 3 to 5, wherein the spline joint interface is a crowned spline interface .

7. The drive shaft device according to any of the

preceding claims, wherein the sleeve element (16) is a gear wheel support sleeve which at one end is anchored in and cantilevered from a carrier element and which forms part of or carries a bearing device (118) that supports a planet pinion of a planet gear stage.

8. The drive shaft device according to any of the

preceding claims, wherein the end of the shaft unit (12; 112), connected to the sleeve element (16) comprises a male spline (18) formed on an outer surface of the shaft unit (12; 112) .

9. The drive shaft device according to any of the

preceding claims, wherein the shaft unit (12; 112) includes a side-sealing piston ring seal (136) for retaining a

lubricating fluid.

10. The drive shaft device according to any of the

preceding claims, wherein the drive shaft device connects a torque-reducing gearbox with a generator unit.

11. The drive shaft device according to any of the claims 1 to 9, wherein the drive shaft device connects a torque- dividing gearbox with a torque-reducing gearbox.

12. An electric power-generating device that converts fluid flow of wind or water to electricity comprising:

a rotor having blades that rotate in response to fluid flow;

a main power input shaft coupled to said rotor;

a torque-dividing gearbox consisting of a gear coupled to said main power input shaft and at least one pinion, teeth of said at least one pinion directly engaging teeth of said gear; and

one or more torque-reducing gearboxes, having an input shaft connected to said at least one pinion, said one or more torque-reducing gearboxes being located around a perimeter of said main power input shaft ;

a shaft unit (12; 112) of a flexible coupling type, an end of which is equipped with said pinion (14) for engagement with said gear of the torque-dividing gear box; and

13. The device of claim 12, wherein the sum of the torques at said at least one pinion is substantially equal to the torque delivered to said torque-dividing gearbox by said main power input shaft .

14. The device of claim 12 or 13, wherein said gearboxes are included in powertrains including generators driven by said torque-reducing gearboxes such that the sum of the power producing capacities of said generators is substantially equal to the maximum power delivered by said power input shaft.