Patent Description:
In particular the invention relates to a gear wheel that can be used for a gearbox or gear transmission between for example a compressor element and a drive.

It is known that compressor elements are driven at great speeds by the drive and are subject to high dynamic process forces.

Consequently, the device is prone to vibration-related problems. Vibrations generated in the compressor element and/or the drive can propagate through the transmission. These vibrations are chiefly caused by an imbalance of the drive and pulsations of the process forces of the compressor element in combination with the occurrence of resonances.

Different dynamic problems occur, both in the drive and in the compressor element.

One of said problems is a combination of torque and the bending of the shaft and compression of the bearings, a combined torque-lateral 'mode-shape' or torque and axial mode-shape or the use of gear wheel pairs with a helix gear mesh.

A solution that uses a flexible coupling between the drive and the compressor element is already a known.

The flexible coupling ensures a dynamic uncoupling between torsional dynamics of the drive and the compressor element.

Furthermore, this will also simplify the alignment between the two and result in a damping of the vibrations.

However, such flexible coupling shows a number of disadvantages:.

This is why a so-called direct coupling is preferred in modern machine design; the floating gear wheel is directly on the motor shaft.

Such direct coupling is very rigid, the result being that all mode shapes are coupled.

Moreover, such coupled modes are very undamped because the damping material of the flexible coupling is not present. Consequently, the drive is prone to dynamic excitations such as imbalance and compression pulsations.

Said combined torque-lateral mode shape i.e. a combination of torque and the bending of the shaft results in a so-called rattle in the gear wheels.

This is caused because certain mode shapes are excited or transmitted by the drive and/or the compressor element.

Gear wheels with spokes, which are used in a transmission to uncouple the dynamics between the drive and the compressor element are already known,.

By using gear wheels with spokes, the gear wheel becomes more torsionally flexible, efficiently preventing the propagation of vibrations, particularly torsional vibrations.

Such gear wheels have the consequence that the eigenfrequencies of certain mode shapes are shifted such that they are not excited.

For certain mode shapes this is not always possible because the gear wheel with spokes cannot be made too weak. Moreover, during the start-up it is still necessary to go through the lowered mode shapes.

<CIT> describes a device for torsional vibration damping in rotating components whereby use is made of rubber elements which are mounted between the rotating components and whereby the torque is transmitted via the rubber elements. This has the disadvantage that there is not only a greater risk of failure of the rubber but also that the rubber will have to be regularly replaced due to wear and tear.

The purpose of the present invention is to improve the properties of gear wheels with spokes, such that the damping value of the transmission can be increased, such that excitation of certain mode shapes can be reduced or avoided and to offer a solution to at least one of the aforementioned and other disadvantages.

To this end, the invention relates to a gear wheel according to claim <NUM>.

This provides the advantage that by filling the free spaces with a block of incompressible material and a viscoelastic material, the gear wheel will show good damping properties for the torque-lateral mode shapes and any other possibly coupled mode shapes.

Said vibrations and the bending of the shaft, will deform the gear wheel with spokes.

Said deformation will compress the viscoelastic material between the block and the gear wheel which will result in damping, whereas the block will ensure that the deformation of the gear wheel remains limited.

It is important to note that by providing the block, or 'core', from incompressible material, it will be possible to compress the viscoelastic material more efficiently between the block and the gear wheel when the gear wheel deforms due to the occurring vibrations, than when said free spaces are completely filled with a viscoelastic material.

An alternative embodiment not according to the claimed invention relates to a gear wheel that is provided with spokes which extend between a rim supporting a gear mesh and a corresponding gear hub, whereby free spaces are located between the spokes which extend between the rim and the gear hub, characterised in that at least one of said free spaces is completely filled with a block, made of a viscoelastic material.

Note that in said embodiment there is no additional viscoelastic material between the gear wheel on the one hand and the block on the other hand.

Such embodiment will also obtain the damping effect as described above.

As it is exactly the compression of the viscoelastic material that will generate the damping properties, providing the block in the free spaces will improve the damping properties of the gear wheel according to the invention.

In a practical embodiment, the viscoelastic material is mounted between the spokes and the block. This material will be loaded in tension and thus provide the damping.

Additionally or alternatively, the viscoelastic material is mounted between, on the one hand, the block and, on the other hand, the gear hub and the rim. The material is loaded on shear to then provide damping again.

Depending on the application for which the gear wheel is to be used, or rather on the expected vibrations in said application and the required damping, the viscoelastic material can be mounted on the desired locations.

Not only the location, but also the amount of viscoelastic material that can be mounted, can be chosen. The nature and composition of the viscoelastic material can also be chosen, as well as the initial compression of the viscoelastic material. The latter is the compression of the viscoelastic material upon mounting the blocks in the free spaces between the spokes.

In a practical embodiment, the viscoelastic material takes on the form of one or more pads or O-rings.

Such pad can be laid between the block and the gear wheel as it were. An O-ring can be mounted around the block.

In a practical embodiment, the block is composed of different partial blocks.

In a practical embodiment extra partial spokes can be added which are only connected to the hub or only to the rim. Said blocks or partial blocks are then placed between a full spoke and a partial spoke.

Viscoelastic material can also be mounted between the different partial blocks which will provide extra damping.

In a preferred embodiment, the blocks are part of, or form one whole with the gear hub.

Grooves will be located between the gear wheel on the one hand and the block on the other hand which are filled with a fluid.

Consequently, a squeeze film damper is formed, which will dampen the torsional vibrations.

The invention further relates to a compressor device comprising:.

characterised in that the transmission comprises at least one gear wheel according to the invention.

This provides the advantage that by applying a gear wheel according to the invention with improved damping properties, the damping value of the transmission can be increased, such that excitation of certain mode shapes can be reduced or avoided.

The gear wheel can be mounted both on a shaft of the drive and on a shaft of the compressor element.

With the intention of better showing the characteristics of the invention, a few preferred embodiments of a gear wheel according to the invention are described hereinafter by way of an example, without any limiting nature, with reference to the accompanying drawings, wherein:.

<FIG> schematically shows a compressor device according to the invention, which in this case is a screw compressor device <NUM> provided with a compressor element <NUM>. It is possible that the screw compressor device <NUM> is provided with more than one such compressor element <NUM>.

The compressor element <NUM> comprises a housing <NUM> in which two rotors <NUM>, <NUM> are mounted with their shafts <NUM>, <NUM> on bearings. These rotors <NUM>, <NUM> are so-called screw rotors, i.e. a male screw rotor <NUM> and a female screw rotor <NUM>, with lobes <NUM> that can rotate cooperatively into each other.

At one end 7a of the shaft <NUM> of one of the rotors <NUM> a first driving gear wheel <NUM> is provided that can engage with a second driving gear wheel <NUM>, whereby said second gear wheel <NUM> is mounted on a shaft <NUM> of a drive <NUM>.

Said drive <NUM> is an electric motor for example.

In this case the driving gear wheel <NUM> is mounted on the male rotor <NUM>, but it can also be mounted on the female rotor <NUM>.

Further, the other end 7b of the shaft <NUM> of said rotor <NUM> and the corresponding end 6b of the shaft <NUM> of the other rotor <NUM>, are each provided with a so-called synchronisation gear wheel <NUM>, <NUM>.

Said gear wheels <NUM> and <NUM> are typically provided with a straight cut gear mesh <NUM> on their relevant rims <NUM>. Said gear wheels <NUM> and <NUM> are provided with a slanted gear mesh. Obviously it is also possible that all gear wheels <NUM>, <NUM>, <NUM> and <NUM> have a straight cut gear mesh or that they all have a slanted gear mesh or another combination.

As is clearly shown on <FIG>, there is no elastic coupling between the electric motor <NUM> and the driven rotor <NUM>.

The transmission between the electric motor <NUM> and the driven rotor <NUM> is provided completely by the driving gear wheels <NUM>, <NUM>.

One of said driving gear wheels <NUM> is provided with spokes <NUM> as shown in <FIG> and <FIG>, which are mounted between the rim <NUM> with the gear mesh <NUM> and the gear hub <NUM> of the gear wheel <NUM>, whereby between the spokes <NUM> free spaces <NUM> are located which extend between the rim <NUM> and the gear hub <NUM>.

In this case the driving gear wheel <NUM> mounted on the motor <NUM> is provided with such spokes <NUM>. Naturally it is not excluded that another or several other gear wheels <NUM>, <NUM>, <NUM> are provided with such spokes <NUM>.

<FIG> and <FIG> clearly show that the driving gear wheel <NUM> is provided with eight spokes <NUM> in this case which extend from the hub <NUM> to the rim <NUM>.

The spokes <NUM> in the example shown, but not necessarily for the invention, are beam-shaped and have a constant cross-section.

According to the invention, at least one of said free spaces <NUM> is filled with a block <NUM> or core made of a rigid, incompressible material.

The block <NUM> is preferably made of, for example, aluminium or polyurethane, but other metal or synthetics are also possible.

As shown in <FIG>, half of the, in total, eight free spaces <NUM> are filled with such block <NUM>, whereby the division of the four blocks <NUM> is symmetrical.

According to the invention and as visible in the crosssections of <FIG>, a viscoelastic material <NUM> is located between the gear wheel <NUM> on the one hand and the block <NUM> on the other hand.

The viscoelastic material <NUM> is in this case, but not necessarily, made of rubber. This rubber can be both natural and synthetic, but other materials can also be applied, such as neoprene.

As is shown in <FIG>, viscoelastic material <NUM> is mounted between on the one hand the block <NUM>, and, on the other hand, the rim <NUM> and the gear hub <NUM>.

Said viscoelastic material <NUM> will cause damping by shear in said material <NUM> and thus reduce the vibration in the mode shapes.

As is shown in <FIG>, viscoelastic material <NUM> is also mounted between the spokes <NUM> and the block <NUM>.

Said viscoelastic material <NUM> will cause damping by tension loads in said material <NUM>.

It is possible that only viscoelastic material <NUM> is located between the spokes <NUM> and the block <NUM>, whereby no viscoelastic material <NUM> is provided between the block <NUM> on the one hand and the rim <NUM> and the gear hub <NUM>, on the other hand.

It is also possible that only viscoelastic material <NUM> is located between the block <NUM> on the one hand and the rim <NUM> and the gear hub <NUM>, on the other hand, whereby no viscoelastic material <NUM> is provided between the spokes <NUM> and the block <NUM>.

The amount of viscoelastic material <NUM> which is provided depends on the damping which is desired or necessary for the relevant application.

in the example of <FIG>, the viscoelastic material <NUM> takes on the form of a number of O-rings <NUM>, in this case four. But this could also only be one, two, three or more than four O-rings.

Said O-rings are tensioned around the block <NUM> as it were.

To this end the block <NUM> is preferably provided with a groove <NUM> or recess provided for this purpose.

Preferably, the viscoelastic material <NUM> is at least partially compressed, this means: even without any torsional or vibrational load the viscoelastic material <NUM> is already partially compressed.

Tests have shown that said so-called pre-load will improve the operation.

Instead of a hard block <NUM> with viscoelastic material <NUM>, it is also possible to choose to make the block <NUM> in viscoelastic material.

Such embodiment will be comparable to the embodiment as shown in <FIG>, with the difference that there will be no viscoelastic material <NUM>.

The operation of the screw compressor device <NUM> and the gear wheel <NUM> is very simple and as follows.

During the operation, the drive <NUM> will drive the second driving gear wheel <NUM>. The operation of the gear wheels will also set in motion the first driving gear wheel <NUM>.

Consequently the male screw rotor <NUM> will be set in motion, whereby the operation of the synchronisation gear wheels <NUM>, <NUM> causes the female screw rotor <NUM> to follow the motion synchronously, in order to enable the gas in the compressor element <NUM> to be compressed.

During the operation, all kinds of dynamic force combinations of the different mode shapes will occur, including for example the combined torsional-lateral bending mode or torsional lateral mode.

Under the influence of the excited mode shape, the second driving gear wheel <NUM> will deform somewhat.

Consequently, the space <NUM> between the spokes <NUM> and the block <NUM> will deform, such that the viscoelastic material <NUM> located there, will be compressed. Consequently, the relevant mode shape is damped.

The extent to which said mode shape is damped depends on the relative deformation of the second driving gear wheel <NUM>, the used damping materials and the pre-load.

<FIG> show a variant according to <FIG>, whereby in this case the block <NUM> is divided into or composed of different partial blocks 20a, 20b.

In this case two partial blocks 20a, 20b are provided.

In two free spaces <NUM> the block <NUM> is divided parallel with the spokes <NUM>, in two other free spaces <NUM> the block <NUM> is divided perpendicular to the spokes <NUM>.

Just as in the previous embodiment, half of the free spaces <NUM> are filled. Of course it is also possible that less or more, or all, free spaces <NUM> are filled.

<FIG> shows a cross-section of the blocks <NUM> which are divided perpendicular to the spokes <NUM>.

<FIG> shows a cross-section of a block <NUM> that is divided parallel with the spokes <NUM>.

Viscoelastic material <NUM> is mounted between the different partial blocks 20a, 20b.

In this case the viscoelastic material <NUM> takes on the form of one or more pads <NUM>, slices, plates or sheets.

The pads <NUM> can be mounted between the blocks <NUM> or between a block <NUM> and the gear wheel <NUM>, whereby they are mounted around the relevant block <NUM> or partial block 20a, 20b.

The pads <NUM> are, as in the previous embodiment, mounted in recesses <NUM> provided for this purpose, but this is not necessarily the case.

It is also possible that the pads <NUM> are constructed of different separate strips.

In this case too the viscoelastic material <NUM> in the form of the pads <NUM> is at least partially compressed.

Although in the example of <FIG> there are always only two partial blocks 20a, 20b per filled free space, it is not excluded that there are several partial blocks 20a, 20b.

By providing many partial blocks 20a, 20b, a sort of lamella-shaped partial blocks 20a, 20b with O-rings <NUM> or pads <NUM> of viscoelastic material <NUM> in between is obtained.

<FIG> shows a variant embodiment of <FIG>, whereby the blocks <NUM> are mounted on a disk <NUM> or plate.

It is also possible that said blocks <NUM> together with said disk <NUM> form one whole, this means: that they are made of one piece of material.

Such structure can also be applied with the variant of <FIG>.

The use of such disk <NUM> is handy in the manufacture of the gear wheel <NUM>, i.e. when mounting or placing the blocks <NUM> in the free spaces <NUM> between the spokes <NUM> of the gear wheel <NUM>.

As can be deduced from <FIG>, the disk <NUM> is located next to the gear wheel <NUM>. It is also possible that the disk <NUM> is located against the gear wheel <NUM>.

<FIG> and <FIG> show another two variants of <FIG>.

In the case of <FIG>, the blocks <NUM> are in direct contact with the gear hub <NUM>. This means that no viscoelastic material <NUM> is located between a block <NUM> and the gear hub <NUM>.

In this case the blocks <NUM> are even part of the gear hub <NUM> or, in other words, they form one whole with it.

Between the blocks <NUM>, on the one hand, and the spokes <NUM> and rim <NUM>, on the other hand, viscoelastic material <NUM> is mounted.

<FIG> shows a same embodiment, but here the form of the blocks <NUM> is different. In this case there is a protrusion <NUM> on the rim <NUM> and an associated recess <NUM> in the blocks <NUM>. Consequently, the blocks <NUM> have a sort of V-shaped cross-section.

<FIG> shows a variant embodiment of <FIG>, whereby the second driving gear wheel <NUM> is in this case provided with a number of partial spokes <NUM>, which are only connected to the gear hub <NUM>. In other words, they do not extend from the gear hub <NUM> up to the rim <NUM> in the same way as the spokes <NUM>.

It is not excluded that the partial spokes <NUM> are only connected to the rim <NUM>.

In this case there are four such partial spokes <NUM>.

The blocks <NUM> are placed in the space between a partial spoke <NUM> and a spoke <NUM>.

The viscoelastic material <NUM> is mounted between the blocks <NUM> on the one hand and the rim <NUM>, the gear hub <NUM>, the spokes <NUM> and/or the partial spokes <NUM> on the other hand.

<FIG> and <FIG> show a last variant of a gear wheel <NUM> according to the invention.

Here, grooves <NUM> are located between the gear wheel <NUM> on the one hand and the block <NUM> on the other hand.

The width, or thickness, of the grooves is preferably less than <NUM> millimetre.

Said grooves are practically realised by for instance EDM or wire electrical discharge machining, and as a result of this possess a bulge <NUM> on their end.

The grooves <NUM> are filled with a fluid.

This fluid possesses viscous properties and is for example, but not necessarily, oil.

In this way squeeze film dampers are formed in the grooves <NUM>.

To ensure the oil in the grooves <NUM> effectively remains in the grooves <NUM> during rotation of the gear wheel <NUM>, the gear wheel <NUM> is provided with two cover plates <NUM> in this case, one on each side of the gear wheel <NUM>, to close the grooves <NUM>.

It is also possible that only one cover plate <NUM> is provided.

It is possible that the cover plates <NUM> completely cover the grooves <NUM>, this means that the fluid in the grooves <NUM> cannot leak out. This has the advantage that as soon as the oil or fluid is injected or inserted in the grooves <NUM>, no more oil is needed.

However, it is possible that the cover plate <NUM> or cover plates <NUM> are provided with drain channels or drain openings for the fluid. <FIG> schematically shows such drain channel <NUM>.

As shown in <FIG> the drain channel <NUM> extends perpendicularly through the cover plate <NUM>, from the side of the cover plate <NUM> oriented to the gear wheel <NUM> in a location located near the grooves <NUM> to the other side of the cover plate <NUM>, i.e. the side of the cover plate <NUM> facing away from the gear wheel <NUM>.

It is important hereby that the drain channel <NUM> is in connection with the groove <NUM> such that a fluid, such as for example oil, can flow from the groove <NUM> to the drain channel <NUM>.

Preferably, such drain channel <NUM> will be provided for every groove <NUM>.

Although the drain channel <NUM> is drawn as a straight channel, which extends in a direction perpendicular to the plane of the cover plate <NUM>, it is not excluded that the drain channel <NUM> is oriented differently.

It is also not excluded that the different drain channels <NUM> provided in the cover plate <NUM> convene in a certain point, whereby from this point one joint channel continues to said other side of the cover plate <NUM>.

Such gear wheel from <FIG> and <FIG> will be applied in a compressor device which is provided with an oil-injection circuit with a nozzle <NUM> or the like which can inject oil in the grooves <NUM> of the gear wheel <NUM>.

The nozzle <NUM> will be placed hereby on the level of the bulges <NUM> of the grooves <NUM>. This is schematically shown in <FIG>.

During the rotation of the gear wheel <NUM> the oil will be injected in the bulges <NUM> and the centrifugal force will force the oil in the grooves <NUM>, such that a squeeze film damper is created in the grooves <NUM>.

The cover plates <NUM> will ensure that the oil remains in the grooves <NUM>, whereby the oil can flow out via the drain channel <NUM>. The oil that flows out is then quickly refilled by injecting new oil with the nozzle <NUM>.

The heat which is inevitably generated during the operation of the compressor device <NUM> will ensure that the viscosity of the oil reduces, such that the damping will decrease.

By injecting fresh oil, and draining oil via the drain channel <NUM>, it is ensured that fresh, cold oil will always be in the grooves <NUM> such that the damping is always optimal.

Furthermore, it is also possible to check the flow of the oil which is injected such that oil is only injected when vibrations and/or resonances occur.

The advantage of this is that oil will only be injected in the gear wheel <NUM> when damping is needed, such that no oil is injected unnecessarily.

The speeds of the compressor device <NUM> for which such vibrations or resonances occur can be pre-defined and the flow of the oil-injection can be regulated to inject oil when the compressor device <NUM> runs at said speeds, but it is also possible to perform real time measurements of the vibrations or resonances during the operation of the compressor device <NUM> and regulate the oil injection based on such measurement.

Although in the example shown a gear wheel according to the invention is applied in a transmission of a screw compressor, it is not excluded that the gear wheel is applied in other machines. The invention is not restricted either to application of a gear wheel according to the invention as a second driving gear wheel, but another gear wheel or a combination of gear wheels of the compressor device can also be executed in this way.

Claim 1:
Gear wheel that can be used for a gearbox or a gear transmission and that is provided with spokes (<NUM>) which extend from a rim (<NUM>) supporting a gear mesh (<NUM>) toa corresponding gear hub (<NUM>), whereby the spokes (<NUM>) are with one end undisplaceably connected to the gear hub (<NUM>) at its outward directed surface and with the other end undisplaceably connected to the rim (<NUM>) at its inward directed curved surface, and whereby free spaces (<NUM>) are located between the spokes (<NUM>) which extend between the rim (<NUM>) and the gear hub (<NUM>), characterised in that at least one of said free spaces (<NUM>) is filled with a block (<NUM>) made of a rigid, incompressible material, whereby between the gear wheel (<NUM>) on the one hand and the block (<NUM>) on the other hand a viscoelastic material (<NUM>) or a viscous fluid is located.