GB2172687A - Flywheels - Google Patents

Abstract

A flywheel includes laminar elements 3 arranged parallel to one another on a shaft 1 which passes through the centres of the elements, an end clamp 2 on the shaft at each end of the arrangement of laminar elements for applying a load to the arrangement across the thickness of the elements, means 5,6 for holding each end clamp in position on the shaft and maintaining the load on the laminar elements, and keying means 18,19 for locating the elements on the shaft, the keying means allowing a limited radial movement of the laminar elements to occur with respect to the shaft. Resilient layers 4 are positioned between each end clamp 2 and the elements 3. <IMAGE>

Description

SPECIFICATION Flywheels This invention relates to flywheels.

Flywheels in the shape of large discs, which may measure many feet in diameter, are known and an application for such flywheels is in the storage of energy.

This invention may be applied to such flywheels, although its application is not limited to flywheels which are of any particular size or shape, or which are employed in any particular use.

A number of different aspects of the invention will be described by way of example with reference to the accompanying drawings in which Figure 1 illustrates diagrammatically a longitudinal section through a flywheel assembly, Figure 2 is a diagrammatic end view of the arrangement shown in Fig. 1, Figure 3 is an enlarged diagrammatic crosssectional view through a part of the arrangement shown in Figs. 1 and 2, Figure 4 is a diagrammatic vertical section through a bearing arrangement for flywheel, and Figure 5 is a vertical cross section through a flywheel within an enclosure.

Referring to Fig. 1, there is shown a flywheel having a central shaft 1, upon which there are mounted, between a pair of end clamps 2, a series of laminar discs 3. A layer of resilient material 4 is positioned between each end clamp 2 and the respective end of the series of laminar discs 3. Nuts or retainers 5 and 6 are arranged within recessed portions of shaft 1 at opposite ends of the assembly.

The shaft 1 is supported at its opposite ends by means of journal bearings 7 and 8.

Flywheels which are made up of a number of laminar discs have the disadvantage that the moments of inertia for bending and torsion of the assembly are not, as in the case with flywheels made of a single piece of material, related to the overall dimensions of the assembly, but are related substantially to the moments of inertia for bending and torsion of the central shaft.

This effect can adversely affect vibrational stability with regard to both bending and torsion, resulting in limitations which would not be present in an equivalent single piece flywheel, although a single piece flywheel has other disadvantages.

The vibrational stability of the flywheel shown in Fig. 1 and made up of a number of laminar discs is improved by applying a load from each end of the assembly via the end clamps 2 and the layers of resilient material 4 to a region of the series of laminar discs 3 surrounding the central shaft 1, as indicated by arrows 9. In this example, these loads are applied between the shaft 1 and the series of discs 3 by preloading the end clamps 2 on to the discs 3 and maintaining the preload by the retainers or nuts 5 and 6. Hydraulic or other means may alternatively be used to produce the effective load.

The layers of resilient material 4 interposed between the respective end discs of the series of discs 3 and the adjacent end clamp pieces 2 are such that relative radial movements between the discs and the end clamps caused by virtue of the different diameters of discs and clamp pieces assuming these are made from similar materials are translated into shear within the material, which is capable of substaining the axial load at the same time.

The interposition of the material 4 reduces the possibility of out of balance loads being generated during acceleration and deceleration due to differences in growth and contraction rates between the discs 3 and the end clamps 2. The thickness of the material 4, and thus the shear angle, selected represents a circumferentially uniform and very small restriction upon the relative radial movements of the discs 3 and end clamps 2.

A high speed laminated fly-wheel, such as that shown in Fig. 1 with laminar disc 3 mounted on a central shaft 1, is also liable to be affected by the development of out-of-balance loads as a result of variations in the size of the bores of the discs as the discs increase and decrease in diameter with the acceleration and deceleration of the flywheel.

An arrangement which minimises the risk of such an out of balance condition will now be described with reference to Figs. 1-3.

An arrow 15 on Figs. 1 and 2 indicates a key station providing a linkage between the shaft 1 and the discs 3. Two further key stations 16 and 17 provide a linkage between the shaft 1 and the discs 3. The key stations 15-17 are similar and only the station indicated by arrow 15 will be described in detail.

The key station indicated by the arrow 15 will now be described with reference to Figs.

1 and 3. As may best be seen in Fig. 3 the key station at 15 comprises a pair of parallel keys 18 and 19 extending along and fixed to the shaft 1 symmetrically about a radial line 20. The discs 3 are each formed with corresponding slots 22 and 23, which provide a radial tongue 24 along the bore of the series of discs 3. The tongue 24 is closely fitted upon one side of each of the keys 18 and 19 so that it has a sliding contact with respect to the keys 18 and 19. There is adequate clearance between the other two exposed faces of each of the keys 18 and 19 and the respective slots 22 and 23 to allow radially symmet ricai movement of the discs with respect to the keys 18 and 19.

By means of this arrangement, it is possible to minimise the effect of changes in clearance, indicated at 25, between the shaft 1 and the discs 3 with variations in rotational speed.

Although, in the embodiment described, the use of three key stations 15-17 has been described in order to maintain the symmetrical location of the discs 3 about the axis of the shaft 1, it will be appreciated that more than three such stations could be employed and that, as an alternative, it could be arranged that elements on the discs 3 could project into longitudinal grooves on the shaft 1 in order to provide a similar effect.

There will now be described with reference to Fig. 4 a composite hydrodynamic/hydrostatic bearing arrangement constituting a low-loss system with safety back-up for use with a flywheel.

In a flywheel arranged with its axis vertical the most critical bearing is the thrust unit normally positioned at the base ofthe shaft. This bearing carries the entire weight of the rotating components and in the event of failure, the assembly risks total destruction. Hydrodynamic bearings exist but the running losses are high-a matter of concern in an efficient flywheel installation. Hydrostatic bearing units also exist in which the entire weight is carried by oil pressure within the bearing.

However, since hydrostatic bearings depend entirely upon a high pressure oil supply being maintained for the successful operation of the flywheel any failure of this supply could be disastrous.

A comparatively economic arrangement, which minimises these problems, is shown in Fig. 4 and includes a central shaft 30 carrying a flywheel body 31 and having a hydrostatic bearing face 32 arranged at its end. A housing 33, which is closed by an end plate 34 carrying a piston 35 which is spring loaded, as indicated at 36, also carries a hydrodynamic bearing 37. The bearing 37 cooperates with a thrust collar 38 on the shaft 30 and the bearing face 32 cooperates with the spring loaded piston 35. The chamber 38 contains oil under pressure.

The arrangement is such that the mass of the rotating body is normally "floated" on the hydrostatic bearing assembly, so that a clearance 42 exists between the surface of the hydrodynamic bearing constituted by the bearing 37 and the collar 38. With this arrangement the high efficiency of the hydrostatic bearing, avoiding high oil shear losses, is normally achieved.

In the event of the failure of the hydrostatic bearing arrangement, the rotation mass is lowered on to the faces of the hydrodynamic bearing 37, 38, which provides a back-up. Rotation of the fly-wheel is thus allowed to continue, although the efficiency of the unit due to the increased running losses will have decreased.

There will now be described with reference to Fig. 5 an arrangement for controlling the temperature rise due to loss of vacuum in an evacuated enclosure containing a rotating flywheel.

A flywheel rotating at high peripheral speeds sustains substantial windage losses when operating at atmospheric pressure. In order to reduce these losses, the flywheel may be closely surrounded by an enclosure from which most of the air is evacuated.

However, any sudden loss of vacuum results in the enclosure being filled with air at atmospheric pressure.

With the flywheel running under loss of vacuum conditions, i.e. at atmospheric pressure with the relatively small volume of air within the enclosure, the flywheel and the air would sustain a rapid and substantial rise in temperature, since the heat produced by the windage losses, at atmospheric pressure, would largely be contained within the enclosure. The temperature rise, depending on the dimensions and speed of the flywheel, could produce a catastrophic failure of the fly-wheel system and enclosure.

In order to restrict the temperature rise to a level predictable and manageable, a sufficient quantity of water is injected into the enclosure so that steam at atmospheric pressure may be produced. This steam is vented in a controlled manner during the time in which the flywheel is brought to rest.

Referring now to Fig. 5, there is shown a flywheel 45 supported on a shaft 46 by bearing assemblies 47 and 48 within an enclosure 49 which is supported at 50. A temperature detector (not shown) is arranged to detect a rise in temperature above a safe value and to inject an appropriate amount of water into the enclosure 49 via water injection points 51 when a critical temperature is reached.

The heat generated by the windage losses and the quantity of water are such that the water is vapourised and is removed via a steam vent 52 in a controlled manner. As a result of this arrangement for removing the excess heat in a controlled manner, the flywheel can be brought to rest in a controlled manner and protection of the flywheel and of personnel in the vicinity are unsured.

Although the invention has been described, by way of example, with reference to particular embodiments, it will be appreciated that variations and modifications may be made within the scope of the invention. For example, although the keys 18 and 19 shown in Fig. 3. are independent of one another, they could be joined together by means of a web and combined into one unit fitting into a single channel in the surface of the shaft 1.

Claims (11)

1. A flywheel including a plurality of laminar elements arranged parallel to one another on a shaft which passes through the centres of the elements, an end clamp on the shaft at each end of the arrangement of laminar elements for applying a load to the arrangement across the thickness of the elements, means for holding each end clamp in position on the shaft and maintaining the load on the laminar elements, and keying means for locating the elements on the shaft, the keying means allowing a limited radial movement of the laminar elements to occur with respect to the shaft.

2. A flywheel as claimed in claim 1 including a respective element of resilient material positioned between each end clamp and the respective end of the arrangement of laminar elements.

3. A flywheel as claimed in claim 1 or claim 2 including a pair of keys projecting from the surface of the shaft and extending longitudinally of the shaft, the adjacent faces of the respective keys being in sliding contact with the opposite faces of a tongue extending from each of the laminar elements, the other faces of the keys extending into the elements with clearance.

4. A flywheel as claimed in claim 3 in which the pair of keys forms a single unit.

5. A flywheel bearing arrangement including a hydrostatic bearing and a hydrodynamic bearing, the arrangement being such that in normal operation the hydrostatic bearing carries the load of the flywheel and that upon failure of the hydrostatic bearing the load is transferred to the hydrodynamic bearing.

6. A flywheel assembly including an evacuated enclosure containing a flywheel, and means which is operative upon loss of the vacuum in the enclosure beyond a given level, to inject water into the enclosure and thereby minimise damage to the flywheel.

7. A flywheel as claimed in any one of chalims 1 to 4 including a bearing arrangement as claimed in claim 5.

8. A flywheel as claimed in any one of claims 1 to 4 forming a part of an assembly as claimed in claim 6.

9. A flywheel as claimed in claim 1 substantially as described herein with reference to Figs. 1 to 3 of the accompanying drawings.

10. A flywheel bearing arrangement as claimed in claim 5 substantially as described herein with reference to Fig. 4 of the accompanying drawings.

11. A flywheel assembly as claimed in claim 6 substantially as described herein with reference to Fig. 5 of the accompanying drawings.