GB2052006A - A bearing and driving assembly - Google Patents

Abstract

A cantilever structure (e.g. windmill sails 1 carried by a nacelle 3) is supported at the top of an upright structure (a tower 4) for rotation about a vertical axis by a bearing and driving assembly comprising first support means 9A/9B/10/14 acting vertically in use for supporting the cantilever structure 1/3 against dropping down the upright structure 4, second support means 16A-16D acting horizontally when operative in use to lock at a selected position the cantilever structure 1/3 against rotation about the vertical axis, and third support means 17A-17D actuable to act horizontally in use in place of the second support means and, whilst so acting, to move to rotate the cantilever structure 1/3 about the vertical axis. The second and third support means include pads 16A-16D and 17A-17D and vertical surfaces that are in frictional engagement when these support means are operative, the use of conventional rotational bearing elements in the second and third support means, which would have to be of much larger size than the pads for similar loadings, being avoided. <IMAGE>

Description

SPECIFICATION Bearing and driving assemblies This invention relates to bearing and driving assernblies for supporting large and heavy machines and structures for movement, for driving the structures to effect such movement, and for holding the structures at desired positions.

Hereinafter there will be particularly described a bearing and driving assembly supporting, at the top of a tower, a nacelle carrying the sails of a windmill but the present assemblies can have other uses, for example supporting and driving the revolving superstructure of a cantilever crane.

Large and heavy structures such as have just been mentioned are usually supported on rollers and tracks or some other form of low friction bearing assembly. In the particular case of a windmill, requirements are (a) that the sails (or turbine rotor) can be slewed to follow changes in wind direction or to be turned out of the wind; (b) that the structure that carries the sails for slewing can be locked in selected positions so that the sails can be held steady in their operational position, or held with their rotational axis at right angles to the wind direction in wind strengths too high for the windmill safely to operate; and (c) that in the locked position the structure carrying the sails should be proof against disturbing forces such as out-of-line wind loads and machinery vibration.If a cantilevered structure is used to carry the sails, and if this structure is supported for slewing by a bearing assembly incorporating wheels running on tracks, the problem arises that insufficient friction force is availahle between wheels and track either for slewing the structure by driving the wheels, or for holding ths structure in a desired position. A separate drive gear mechanism can be provided but this leads to increased construction costs which are particularly high if a mechanism of large size is required, maintenance becomes more complex and hence costly, and back--lash in the gear mechanism is a further problem. Brake mechanism is also required to hold the structure at the desired position, again increasing construction and maintenance costs.As an alternative, some form of high friction material such as rubber could be applied to the wheels and/or the track but very large bearing areas would be required to cope with the loads present in a windmill of large dimensions and brake mechanism for the wheels would still be required.

According to the present invention there is provided a bearing and driving assembly by which a cantilever structure can be supported from an upright structure and can be rotated about a vertical axis into, and held at, selected positions relative to the upright structure, the total mass of the cantilever structure acting at a point displaced horizontally from said vertical axis; the assembly comprising first support means acting vertically in use for supporting the cantilever structure against dropping down the upright structure, second support means acting horizontally when operative in use to lock the cantilever structure against rotation about said rotational axis this support means being held in its operative condition by the action of said total mass, and third support means actuable to act horizontally in use in place of said second support means and, whilst so acting, to move to rotate the cantilever structure about said vertical axis; said second and third support means including pads and vertical surfaces that are in frictional engagement when the support means are operative.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-- Figure 1 is a schematic perspective view of the upper end of a windmiii tower and of a nacelle at the top of the tower, that supports the sails of the windmill, forces acting in one position of the nacelle with respect to the tower being illustrated.

Figure 2 is a schematic sectional side view of the tower top and nacelle of Figure 1, Figures 3, 4 and 5 are sectional plan views on line Ill-Ill, staggered line IV--IV and line V-V respectively of Figure 2 except that components are shown in a difFerent operational position in Figure 4, and Figure 6 is a schematic side view illustrating operation of a part of a bearing and driving assembly by which the nacelle is supported on the tower top.

The windmill, parts of which are shown in the Figures, is of cantilever form, the sails 1 of which are carried for rotation about a horizontal axis 2 by the nacelle 3 which is itself supported at the top of the tower 4 for slewing about a vertical axis 5 by the bearing and driving assembly to be described below.

The tower 4 can be of reinforced concrete and in the particular windmill illustrated is 8 m in diameter and supports the nacelle 3 such that the horizontal axis 2 is 45 m above the base of the tower. The sail diameter is 60 m and its hub is at 1 5.4 m from the vertical axis 5. In Figure 1, 6 is a scale human figure.

The nacelle 3 can be of structural steel with a cladding. The windmill illustrated is for generating electricity and to this end the nacelle contains in the region indicated at 7 in Figure 1 a gearbox and a generator driven, through the gearbox, by the sails. In this use, therefore, the sails constitute a turbine rotor and will hereinafter be referred to as such. Within the tower 4 there is an access-way (not shown) from the base of the tower to the interior of the nacelle and in the base of the tower (also not shown) instrumentation and switch gear rooms are provided.

A windmill of the size illustrated can generate of the order of 3.7 Mw of electricity when operating in a 22 m/sec wind, the sails revolving at 34.1 r.p.m.

The positioning of the turbine rotor, and of the gearbox and generator at the region 7, is such that the centre of gravity of the unit formed by the nacelle and the turbine rotor is at 8 in Figure 2. In the particular embodiment being described the total mass of equipment, nacelle structure and turbine rotor is 233 tonne and the centre of gravity 8 is at 9.21 m from the axis 5 about which the nacelle slews.

There is thus a positive toppling moment created by the offset action of this total mass acting about two rollers 9A, 9B included in the bearing and driving assembly by which the nacelle 3 is supported at the top of the tower 4. These two rollers 9A, 9B are disposed, as viewed in plan (Figure 3), one on each side of the axis 2 about which the turbine rotor rotates, and the centre of gravity 8 is at 6.91 m from a line struck through these rollers.The rollers 9A, 9B are equi-distant from the axis 2 supported, by a beam 1-0, each for rotation about a horizontal axis 11 A or 11 B. For equalising the loads on the rollers the beam 10 is pivotally supported in the nacelle 3 by a horizontal pin 1 2 centrally disposed between the rollers 9A, 9B.With the beam 10 horizontal the axes 11 A, 11 B of the rollers gA,9B intersect one another at a point 1 3 on the axis 5. This point 1 3 is at the centre of a circular track 14 having a horizontal bearing surface 1 5 on which the rollers 9A, 9B run. The components 9A/9B/10/14 of the bearing and driving assembly constitute a first support mechanism of the assembly that acts vertically to support the nacelle and turbine rotor against dropping down the tower.

The bearing and driving assembly further includes an arrangement of fixed upper bearing pads 1 6A, 16E and fixed lower bearing pads 16C, 1 6D; and movable upper bearing pads 1 7A, 1 7B and movable lower bearing pads 17C, 17D. Each bearing pad has a friction surface that is upright and that co operates, in the embodiment illustrated, with an upper or lower track 1 8 or 1 9 carried by the tower 4 and having a vertical face for the pads to bear upon. Alternatively the pads could co-operate directly with the tower surface.

The fixed bearing pads are mounted on support frameworks 20 in the nacelle 2, so as to be fixed in the nacelle, such that with the axis 2 horizontal they are urged by the toppling moment created by the offset action of the total mass of the nacelle and the turbine rotor (acting at the centre of gravity 8) into frictional engagement with the tracks 1 8 and 19 thereby to lock the nacelle to the tower.This is the position illustrated in Figures 1 to 3 and 5 and it will be understood that this locking action of the second support mechanism, which is constituted by the fixed bearing pads 16A to 1 6D and the tracks 18, 1 9 and which acts horizontally, is brought about because the bearing pads 16A and 1 SB are vertically separated from the bearing pads 16C and 16D, and because it is the bearing pads 1 6A, 1 SB that are more remote from the centre of gravity 8 that are above the bearing pads 16C,16D which are nearer the centre of gravity 8.

Each fixed bearing pad 1 6A, 1 SB,.1 60, 1 6D has disposed near it one of the movable bearing pads 1 7A, 17B, 17C, 17D. Each movable bearing pad is pivotally mounted, for movement with respect to the nacelle, at one end of a horizontal arm 21 the other end of which is pivotably secured to a wheel 22 eccentrically of the vertical axis about which the wheel 22 is rotatable. Near the pivotal connection of the pad to the arm 21 one end of a horizontal lever 23 is pivotally connected to the arm 21, the other end of this lever 23 being pivotably connected to a wheel 24 eccentrically of the vertical axis about which this wheel 24 is rotatable. Each lever 23 extends transversely to one side of the arm 21 to which it is connected.Rotation of each wheel 24 imparts reciprocating motion to the lever 23 connected thereto, which lever in turn imparts reciprocating motion to the arm 21 to which it is connected.

In the nacelle-locked position (illustrated in Figures 1 to 3 and 5 and 6) in which the fixed bearing pads 1 SA, 1 SB, 1 60, 1 6D bear on the tracks 1 8, 1 9 the driving crank mechanisms constituted by the arms 23 and their wheels 24 are positioned such that the driven crank mechanisms constituted by-the arms 21 and their wheels 22 hold the movable bearing pads 17A, 17B, 17D, l7Eclearofthetracks 18, 1 9 (see in particular Figure 6).The nacelle is thus held against slewing by the frictional contact between the pads 1 6A, 1 6B, 1 6C, 1 6D and the tracks 18, 19 the vertical weight of the turbine rotor and of the nacelle and the equipment therein being carried by the rollers 9A and 9B, and the movable bearing pads 17A, 17B, 17C, 17D are inoperative. Back-lash is minimised by making the pads resistant to distortion and the support framework 20 therefor resistant to deflections.

When it is desired to slew the nacelle all the wheels 24 are rotated'in unison, the wheels 22 therefore also rotating but these wheels also can be positively driven to rotate if this is necessary, so that the movable bearing pads 17A, 17B, 17C, 17D are moved by the driving and driven crank mechanisms 23/24, 21/22 each to follow the locus indicated by dotted lines 25A and chain dot ines 25B in Figure 6.The path 25A/'25B is such that in one rotation of each wheel 24 and 22 together the pads 1 7A, 1 7B, 1 70, 1 7D first move into frictional engagement with the tracks 1 8 and 19, then pivot the nacelle relative to the tower about a horizontal axis in opposition to the toppling- moment discussed above so that the fixed bearing pads 16A, 1 6B, 16C, 1 6D are moved clear of the tracks 18 and 19 then permit the nacelle to pivot back to be again supported by the fixed bearing pads, and finally themselves move clear of the tracks again. Referring to Figure 6, the movable bearing pads are clear of the tracks 18, 19 whilst moving along the dotted line path portions 25A, and are in frictional engage ment with the tracks 1 8, 1 9 whilst moving along the chain-dot line path portions 25B. Whilst the fixed bearing pads are clear of the track 1 8 and 1 9, and the movable bearing pads are in frictional engage ment with the tracks 1 8 and 19 and are moving along the path portions 25B, the movable bearing pads not only act to bring about the clearance between the fixed bearing pads and the tracks 18, 1 9, they also cause the nacelle 3 to slew about the vertical axis 5.It will be appreciated, therefore, that the third support means of the assembly which is constituted by the movable bearing pads 1 7A to 1 7D and the tracks 18,19, is actuable to.acthorizontally in place of the second support means constituted by the fixed bearing pads 16A to 16D and the tracks 18, 19 and, when so acting, to move to rotate the-nacelle about the vertical axis 5.

By repeated rotation of the wheels 24, step wise slewing motion of the nacelle:3 is brought about The direction in which the nacelle 3 is slewed- is selected by selecting an appropriate direction of rotation of the wheels 24.

It will be appreciated that in the Figures the driving and driven crank mechanism 23/24,21/22, are only shown in schematic--form but the basic principles of practical forms of these mechanisms would be as described herein. It is to be understood however, that mechanism utilising these principles:will be of relatively simple form. Mechanisms incorporating jacks in place of some or all of the components of the crank mechanisms described could be utilised for moving the movable bearing pads, whilst retaining a simple form of construction and drive.

As so far described the slewing motion of the nacelle is a step-wise ane. If desired, there can be more than one set-of movable bearing pads, two or three sets being envisaged as preferable, the action o.f each set being arranged to overlap that of another so that more nearly continuous slewing motion can be imparted to the nacelle. It can be arranged that the movable bearing pads are retractable at any point along their paths 25A/25B so that the fixed bearing pads can be re-engaged with the tracks at any point in a cycle of movement of the movable bearing pads.

Maintenance is facilitated since work can be carried out on the fixed bearing pads with the movable bearing pads held: locked in a position in which the fixed bearing pads are held clear of the tracks 1 8, 1 9. Similarly, the movable bearing pads can be worked upon when they are clear of the tracks 18 and T9.

All pads can be of a size very much- smaller than would be required of a roller carrying similar loadings. No separate braking mechanism for locking the nacelle against slewing motion is required as this function is performed by the fixed bearing pads.

It is to be noted that the top of the tower can be left open for inspection purposes. As the load on the rollers carrying the vertical-weight is equalised by supporting them on the free-to-pivot beam (or some equivalent form a load-equalising suspension) the bearing assembly as whole is equivalent to a five point suspension of the nacelle against the tower side wall and top face with all suspension points tending to load share without redundancy. The contact surfaces of the rollers have to be of good form but the tracks can undulate to some extent without undue ill effects and no great precision is required in the motion of the bearing pads with respect to the tracks.Subject to the shear stiffness of the fixed bearing pads the nacelle is rigidly connected with the tower by a self-locking arrangement except when it is moving to a new position, and this self-locking arrangement can be made fail safe. No power is used to hold the nacelle at a desired orientation.

It has been mentioned above that it should be possible, at wind strengths too high for the windmill to operate, to move the turbine rotor into a position such that its axis of rotation is at right angles to the wind direction. In the case of a two-bladed rotor (as illustrated) the rotor will be held locked against rotation, at this position, with one end of one blade facing into the wind. In the particular embodiment - described above the following conditions pertain when the nacelle is parked at right angles to a 60 m/sec wind.

Total weight of nacelle structure, equipment therein and turbine rotor = 233 tonne acting, at 6.91 m from the rollers 9A, 98 (arrow X in Figure 1).

Wind force (SO m/sec wind) acting on side of nacelle 61 6 kN acting at 7.96 m from the axis 5 about which the nacelle slews (arrow Y in Figure 1) giving a moment tending to cause the nacelle to slew = 4904 kNm.

In Figure 1 arrows X and Y indicate the weight and wind force just discussed, and the-reaction loads on the rollers 9A and 9B and the fixed bearing pads 16A, 16, 16C; 16D are indicated by the arrows 16a, 1 Sb, 1 S'c, and 1 sod. These loads are as follows: 9a = 1143 kN 9b = 1143 kin 16a = 2833kN 16b = 1229kN 16c = 356kN 16d = 3706 kN The total load on the fixed bearing pads when resisting skidding = 8-124 kN x ,u4 m acting at 4 m radius.

The friction torque available to resist skidding = 8124 kN x u4 m.

Torque causing skidding (60 m/sec wind) = 4904 kN.

Coefficient of friction required to resist skidding, 4904 y= =0.15 8124 x 4 The required coefficient of friction can be reduced, but only marginally, if provision is made for driving and breaking the rollers 9A and 9B, as follows:- Total load on rollers = 2286 kN acting at 3.5 m radius.

The coefficient of friction to resist skidding, 4909 81 = =0.12 (8124-x 4) + (2286 x 3.5) Approximate generally accepted values for the coefficient of friction for various materials are as follows: MATERIAL CONDITIONS OF USE jEt Steel on steel frosty weather 0.09 dry 0.26 dry with sanding fear 0.15 Timber on metal dry - depending on quality 0.2 to 0.6 Rubber on concrete wet 0.4 to 0.75 dry 0.6 to 0.85 Rubber on metal dry 0.4 Leathern metal dry 0.5 wet 0.36 greased 0.2 Brake lining on steel dry 0.4 to 0.5 It will be seen that the friction available from steel rollers running on steel tracks would be insufficient to provide any safety factor against skidding, particularly in inclement weather conditions.

All the other materials listed provide a sufficiently high coefficient of friction but it will be appreciated that rollers covered with high friction material would be very large.

The movable bearing pads are shod in the same material as the fixed bearing pads to provide the traction necessary to follow changes of wind direction in storm conditions.

Although a windmill has been described in detail, a bearing and driving assembly such as described can be utilised to support other large structures for slewing motion, for example the revolving superstructure of a cantilever crane.

Claims (11)

1. A bearing and driving assembly by which a cantilever structure can be supported from an upright structure and can be rotated about a vertical axis into, and held at, selected positions relative to the upright structure, the total mass of the cantilever structure acting at a point displaced horizontally from said vertical axis; the assembly comprising first support means acting vertically in use for supporting the cantilever structure against dropping down the upright structure, second support means acting horizontally when operative in use to lock the cantilever structure against rotation about said vertical axis this support means being held in its operative condition by the action of said total mass, and third support means actuable to act horizontally in use in place of said second support means and, whilst so acting, to move to rotate the cantilever structure about said vertical axis; said second and third support means including pads and vertical surfaces that are in frictional engagement when these support means are operative.

2. A bearing and driving assembly as claimed in claim 1, wherein said first support means comprises two rollers on a common support that is carried by one of the two structures, and a circular horizontal bearing surface for these rollers that is carried by the other of the two structures and that is centered on said vertical axis, the rollers being one on each side of, and equidistant from, a horizontal axis that intercepts said vertical axis and about which said common support can pivot; the rotational axes of the rollers intersecting one another at a point on said vertical axis when said common support is horizontal.

3. A bearing and driving assembly as claimed in claim 1 or 2, wherein said second support means comprises upper and lower bearing pads carried by one of the two structures fast therewith to constitute fixed bearing pads, and upper and lower vertical bearing surfaces for the upper and lower pads respectively carried by the other of the two structures, the relative dispositions of the fixed bearing pads and the vertical bearing surfaces being such that with the cantilever structure in a horizontal disposition this second support means is operative with these pads and bearing surfaces urged into frictional engagement with each other by a toppling movement created by the cantilever structure.

4. A bearing and driving assembly as claimed in claim 3, wherein said third support means comprises upper and lower movable bearing pads carried by one of the two structures for engagement with said upper and lower vertical bearing surfaces carried by the other of the two structures; the movable bearing pads being actuable to bear on the vertical bearing surfaces to pivot the cantilever structure relative to the upright structure about a horizontal axis in opposition to said toppling moment, thereby to disengage the fixed bearing pads from the vertical bearing surfaces, and thereafter being movable whilst frictionally engaged with the vertical bearing surfaces to rotate the cantilever structure about said vertical axis.

5. A bearing and driving assembly as claimed in claim 4, wherein each movable bearing pad is operated by an associated crank mechanism.

6. A bearing and driving assembly as claimed in claim 4, wherein each movable bearing pad is operated by an associated jack mechanism.

7. A bearing and driving assembly as claimed in claim 4, 5 or 6, wherein in their inoperative positions the movable bearing pads are clear of their associated vertical bearing surfaces, each movable pad when moved moving in one direction only around a locus from this inoperative position to engage its associated bearing surface, disengage the fixed bearing pads from the vertical bearing surfaces, rotate the cantilever structure, disengage from its associated bearing surface and return to its inoperative position.

8. A bearing assembly as claimed in claim 7, wherein each pad can be retracted directly to its inoperative position from any point on said locus.

9. A bearing assembly as claimed in any one of claims 4 to 8, wherein the movable bearing pads constitute a first set of such pads, and wherein the second support means comprises one or more further sets of such pads, corresponding pads of each set being associated with one another with the action of associated pads overlapping one another when the pads are moved.

10. A bearing and driving assembly as claimed in any one of the preceding claims, wherein the upright structure is a tower and the cantilever structure supported therefrom by the bearing and driving assembly is a nacelle carrying the sails of a windmill.

11. A bearing and driving assembly substantially as hereinbefore described with reference to the accompanying drawings.