GB2459110A

GB2459110A - Flywheel containment

Info

Publication number: GB2459110A
Application number: GB0806472A
Authority: GB
Inventors: Jonathan James Robert Hilton; Douglas Isaac Lascelles Cross
Original assignee: Flybrid Systems LLP
Current assignee: Flybrid Systems LLP
Priority date: 2008-04-10
Filing date: 2008-04-10
Publication date: 2009-10-14
Anticipated expiration: 2028-04-10
Also published as: GB0806472D0; GB2459110B

Abstract

Containment means for a flywheel comprises a containment cylinder 8 and, preferably, containment discs 10, 12 located between the flywheel 4 and the housing 6. Normally, a locating pin 32 maintains the cylinder 8 in a stationary position relative to the housing 6 but, if the flywheel begins to fail and break up, the pin 32 is sheared allowing the cylinder 8 to spin freely as it is struck by debris particles breaking off from the flywheel 4, thereby reducing the velocity differential between the flywheel 4 and cylinder 8, and thereby reducing the force with which the debris strikes the cylinder 8. The containment cylinder 8 may be formed of a set of layers (28, fig.4) of unidirectional fibres, interspersed with layers (30) having fibres at a relative 45 orientation.

Description

High Speed Flywheel This invention relates to flywheels, and particularly to high speed flywheels for use in vehicles.

Flywheels typically comprise a relatively heavy mass, arranged to rotate around a shaft. The flywheel is contained within a housing, and bearings are provided to rotatably locate the shaft in the housing. Flywheels can be used in vehicles, for example as an aid for acceleration or deceleration of the vehicle. It is also known to use a flywheel as a battery, whereby the kinetic energy of the flywheel is converted into electrical energy.

The kinetic energy of a flywheel is directly proportional to the rotational inertia and the square of the angular velocity. A flywheel used for energy storage in a vehicle must achieve an optimum balance of mass, inertia and rotational speed. The faster the flywheel can be made to rotate, the smaller and lighter it will be for a given energy storage capacity. A high speed flywheel for use in a vehicle typically run at 25,000 revolutions per minute or higher.

Flywheels used ln vehiclesare subject to particular limitations -Firstly, the speed at which a flywheel within a vehicle can operate is limited by susceptibility to vibration caused on operation of the vehicle, which can cause significant strain on the flywheel mounting and bearings, thereby increasing friction and wear and reducing the efficiency of the flywheel, and furthermore constituting a potential safety risk. The susceptibility of the

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flywheel to vibration can be minimised by providing a flywheel which has a high natural frequency of vibration.

For the above reasons, flywheels in vehicles must adhere to stringent safety criteria, including provision of a benign, or at least controllable, failure mode. When the primary failure mode, i.e. the mode which occurs at the lowest rotational speed, is reached, the flywheel and its housing must be designed to contain all debris generated on the breaking up of the flywheel components.

On failure of a flywheel, the large amount of kinetic energy stored in the flywheel dissipates very quickly and a large instantaneous pressure is generated within the flywheel housing. The flywheel begins to break up into small debris particles, for example in the form of dust. The debris particles are ejected with a high inertia, tangentially away from the flywheel as it continues to spin. The debris strikes the housing, which must be sufficiently strong to contain the high inertia particles. The force with which the debris particles strike the housing is dependent upon the size of the particles and the speed with which they strike the housing, and therefore the speed at which the flywheel is continuing to spin.

An aim of the present invention is to address the problems encountered on failure of a flywheel, and particularly to provide an improved containment means for a high speed flywheel for use in a vehicle, for example for energy storage.

Accordingly the present invention provides, in a first aspect, containment means for a high speed flywheel as claimed in claim 1 of the appended claims.

An advantage of the present invention is that in a failure mode of the flywheel, the containment cylinder is independent of the housing, and is free to rotate on the failure of the flywheel. After impact from debris, the containment cylinder spins in the same direction as the flywheel, therefore the velocity differential between the containment cylinder and the flywheel is less than that which would exist between a stationary housing and the flywheel. Therefore, because the force with which debris particles strikes the containment cylinder is dependent upon this velocity differential, a debris particle of a given size strikes the containment cylinder with a reduced force compared to that with which it would strike the housing if the containment cylinder was not present. The damage to the containment cylinder is therefore less than that which is caused to the housing in prior art embodiments, thus reducing the potential for failure of the housing to contain debris particles. As the debris particles strike the containment cylinder with a reduced force compared to prior art embodiments, the containment cylinder can be of a reduced thickness compared prior art flywheel housings.

Preferably the containment cylinder is formed of a plurality of composite fibre layers. The layers may include a first set of layers having fibres in a first orientation, and a second set of layers having fibres in an orientation different to that of the first set of layers. The first set of layers may be interspersed with the second set.

The type of fibres and combination of layers can be selected to provide a required balance of strength and toughness.

In a preferred embodiment, the first set of layers has fibres orientated unidirectionally and circumferentially around the containment cylinder, and the second set has fibres orientated at 45° to the first set.

The containment means may further comprise containment discs, located axially between the flywheel and the housing. The containment cylinder and containment discs may be manufactured separately, thereby reducing manufacturing costs by enabling mass production. For example, the containment means may comprise a containment cylinder and two containment discs. The containment cylinder and containment discs could each be manufactured from long tubes of material sliced into sections.

Furthermore, the separate parts allow a much closer fit of the containment means within the housing than would be possible if the parts were integral.

The retaining means may comprise a locating pin, positioned in a first recess provided in the containment means and in a second recess provided in the housing, wherein the locating pin is sheared on failure of the flywheel.

The present invention comprises, in a further aspect, a high speed flywheel arrangement including the containment means of the first aspect of the invention.

An embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a side elevation of a flywheel apparatus in accordance with the present invention; Figure 2 is a cross sectional view of the flywheel apparatus of Figure 1 along the lines 11-11.

Figure 3 is a detailed view of the section III indicated in Figure 2.

Figure 4 is a partial isometric view of the inner containment means of the flywheel apparatus of Figure 1.

Referring to Figures 1 and 2, the flywheel apparatus 2 comprises a flywheel 4 having a rim 14. The flywheel 4 is located in an aluminium housing 6 which includes a cylindrical section 6. Inner containment means are located between the flywheel 4 and the housing 6. The inner containment means comprises a composite containment cylinder 8 and two composite containment discs 10, 12. The containment cylinder 8 is located radially between the flywheel rim 14 and the cylindrical section 16 of housing 6, at a small clearance of 3mm from the flywheel rim 14.

The composite containment discs 10, 12 are located axially between the flywheel 4 and side sections 18, 20 of the housing 6. The discs 18, 20 are maintained in position by compression by the side sections 18, 20 of the housing 6, and are restrained from radial movement by annular shoulders 22, 24 provided on the internal profile of the housing 6.

As illustrated in Figure 3, the containment cylinder 8 comprises a plurality of fibre layers 26 arranged circumferentially around the containment cylinder 8, and held together with a resin matrix. The layers 26 comprise a first set 28, having uni-directional fibres, interspersed with a second set 30, having fibres at a +1-45 orientation relative to the first set 28. The layered composition of the containment cylinder 8 is such that highly anisotropic properties result, i.e. the cylinder has a much higher circumferential strength than axial strength.

In normal use of the flywheel apparatus 2, i.e. when the flywheel 4 is in operational use and rotating within the housing 6, the containment cylinder 8 is retained in position in relation to the housing 6 by retaining means comprising a locating pin 32, located in a first recess 34 in the containment cylinder 8 and in a corresponding second recess 36 in the cylindrical section 16 of the housing 8. During normal operation of the flywheel 4, the containment cylinder 6 is prevented from rotating by the locating pin 32. The velocity differential between the rotating flywheel 6 and the stationary containment cylinder 8 is at a first level.

In a failure mode, i.e. when the flywheel 6 begins to fail and break up, debris particles from the flywheel strike the containment cylinder 8, thereby dissipating the kinetic energy of the failing flywheel. In the failure mode, the minimal clearance between the flywheel rim 14 and the containment cylinder 8 provides that the impact of the debris particles of the outer parts of the flywheel rim 14 is substantially in a circumferential direction. The effect of this impact is to shear the locating pin 32 and thus allowing the containment cylinder 8 to spin. A low coefficient of friction between the outer layer 38 of the containment cylinder and the internal face 40 of the cylinder part 16 of the housing 6 minimises resistance to the spinning of the containment cylinder 8.

Because the containment cylinder 8 is spinning, the velocity differential between the flywheel 6 and the containment cylinder 8 is reduced to a second level, which is lower that the first level, thus minimising damage caused to the containment cylinder, whilst protecting the housing.

It has been found that up to 5% of the energy of the particles being ejected from a failing flywheel 6 is deflected axially. The containment discs 10, 12 therefore act to contain the axially deflected force. The housing 6 is sufficiently strong to maintain the containment discs 10, 12 in position, however, the containment discs are also free to rotate on failure of the flywheel 6.

A flywheel apparatus 2 as described above, having a containment cylinder weighing approximately 700g, is sufficiently strong to contain an internal pressure within the housing of up to 1150 bar with a 30% safety margin. In the unlikely event of failure of the containment cylinder 8, failure by cracking would begin in the innermost fibre layer 42. The multitude of layers would prevent fast propagation of the crack throughout the containment cylinder 8, therefore allowing the failing containment cylinder 8 to contain flywheel debris particles, thus protecting the housing 6, for longer.

In alternative embodiments, the properties of the layers of the containment cylinder 8 can be varied. For example, the type of fibre, and the relative orientation of the fibre layers, can be selected according to required strength.

Claims

Claims 1. Containment means for a high speed flywheel contained in a housing, comprising a containment cylinder located radially between the housing and the flywheel, and retaining means, wherein the retaining means maintains the containment cylinder in a stationary position relative to the housing, and wherein in a failure mode, flywheel particles strike the containment cylinder thereby dissipating kinetic energy of the flywheel, and wherein in the failure mode the retaining means is overcome, thereby allowing the containment cylinder to rotate within the housing.
2. Containment means as claimed in Claim 1, wherein the containment cylinder comprises multiple fibre layers.
3. Containment means as claimed in Claim 2, wherein the containment cylinder multiple fibre layers comprise a first set of layers having fibres in a first orientation, and a second set of layers having fibres in an orientaUon different to that of the first set of layer 4. Containment means as claimed in Claim 3, wherein the first set of layers is interspersed with the second set.5. Containment means as claimed in Claim 2 or Claim 3, wherein the first set of layers has fibres orientated unidirectionally and circumferentially around the containment cylinder, and the second set has fibres orientated at 45° to the first set.6. Containment means as claimed in any of the preceding claim wherein the containment cylinder weighs up to 700g.7. Containment means as claimed in any of the preceding claims, wherein the containment means further comprise at least one containment disc, located axially between the flywheel and the housing.8. Containment means as claimed in claim 7, having a containment cylinder and two containment discs.9. Containment means as claimed in claim 7 wherein the at least one containment disc is free to spin on failure of the flywheel.10. Containment means as claimed in any of claims 7 to claim 9 -capable of maintaining an internal pressure within the housing of at least 1150 bar.11. Containment means as claimed in any of the preceding claims wherein the retaining means comprises a locating pin, positioned in a first recess provided in the containment means and in a second recess provided in the housing, wherein on the locating pin is shearable on failure of the flywheel.12. A high speed flywheel arrangement including the containment means of any of claims ito 10.13. Containment means for a high speed flywheel arrangement substantially as hereinbefore described and with reference to the accompanying figures.14. A high speed flywheel arrangement substantia!ly as hereinbefore described and with reference to the accompanying figures.Amendments to the c'aims have been fi'ed as follows Claims 1. Containment means for a high speed flywheel contained in a housing, comprising a containment cylinder located radially between the housing and the flywheel, and retaining means, wherein the retaining means maintains the containment cylinder in a stationary position relative to the housing, and wherein in a failure mode, flywheel particles strike the containment cylinder thereby dissipating kinetic energy of the flywheel, and wherein in the failure mode the retaining means is overcome, thereby allowing the containment cylinder to rotate within the housing, wherein the containment cylinder comprises multiple fibre layers.2. Containment means as claimed in Claim 1, wherein the containment cylinder multiple fibre layers comprise a first set of layers having fibres in a first orientation, and a second set of layers having fibres in an orientation different to that of the first set of layers.3. Containment means as claimed in Claim 2, wherein the first set of layers is interspersed with the second set.
4. Containment means as claimed in Claim 2, wherein the first set of layers has fibres orientated unidirectionally and circumferentially around the containment cylinder, and the second set has fibres orientated at 45 to the first set.
5. Containment means as claimed in any of the preceding claims wherein the containment cylinder weighs up to 700g.
6. Containment means as claimed in any of the preceding claims, wherein the containment means further comprise at least one containment disc, located axially between the flywheel and the housing.
7. Containment means as claimed in claim 6, having a containment cylinder and two containment discs.
8. Containment means as claimed in claim 6 wherein the at least one containment disc is free to spin on failure of the flywheel.
9. Containment means as claimed in any of claims 6 to claim 8 capable of maintaining an internal pressure within the housing of at least 1150 bar.
10. Containment means as claimed in any of the preceding claims wherein the retaining means comprises a locating pin, positioned in a first recess provided in the containment means and in a second recess provided in the housing, wherein the locating pin is shearable on failure of the flywheel.
11. A high speed flywheel arrangement including the containment means of any of claims 1 to 9.
12. Containment means for a high speed flywheel arrangement substantially as hereinbefore described and with reference to the accompanying figures.
13. A high speed flywheel arrangement substantially as hereinbefore described and with reference to the accompanying figures.