Patent Description:
More particularly, the present invention relates to an improved vacuum pumping system which is more reliable compared to prior art vacuum pumping systems, as well as lighter and more compact than such prior art vacuum pumping systems.

Vacuum pumps are used to achieve vacuum conditions, i.e. for evacuating a chamber (so-called "vacuum chamber") for establishing sub-atmospheric pressure conditions in said chamber. Many different kinds of known vacuum pumps - having different structures and operating principles - are known and each time a specific vacuum pump can be selected according to the needs of a specific application, namely according to the degree of vacuum that is to be attained in the corresponding vacuum chamber.

In general, a vacuum pump comprises a pump housing, in which one or more pump inlet(s) and one or more pump outlet(s) are provided, and pumping elements, arranged in said pump housing and configured for pumping a gas from said pump inlet(s) to said pump outlet(s): by connecting the pump inlet(s) to the vacuum chamber, the vacuum pump allows the gas in the vacuum chamber to be evacuated, thus creating vacuum conditions in said chamber.

More specifically, several different kinds of vacuum pumps are known in which the pumping elements comprise a stationary stator and a rotatable rotor, which cooperate with each other for pumping the gas from the pump inlet(s) to the pump outlet (s). In such vacuum pumps, the rotor is generally mounted to a rotating shaft which is driven by a motor, namely by an electric motor.

By way of example, a vacuum pumping system according to prior art is schematically shown in <FIG>.

In the example shown in <FIG> the vacuum pumping system <NUM> comprises a rotary vane vacuum pump <NUM>; rotary vane vacuum pumps are generally used to attain low vacuum conditions, i.e. in a pressure range from atmospheric pressure down to about <NUM>-<NUM> Pa.

As shown in <FIG>, a conventional rotary vane vacuum pump <NUM> generally comprises an outer housing <NUM>, receiving an inner housing <NUM> within which a stator surrounding and defining a cylindrical pumping chamber <NUM> is defined. The pumping chamber <NUM> accommodates a cylindrical rotor <NUM>, which is eccentrically located with respect to the axis of the pumping chamber <NUM>; one or more radially movable radial vanes <NUM> (two in the example shown in <FIG>) are mounted on said rotor <NUM> and kept against the wall of the pumping chamber <NUM> by means of springs <NUM>.

During operation of the vacuum pump <NUM>, gas is sucked from a vacuum chamber through an inlet port <NUM> of the pump and passes, through a suction duct <NUM>, into the pumping chamber <NUM>, where it is pushed and thus compressed by vanes <NUM>, and then it is exhausted through an exhaust duct <NUM> ending at a corresponding outlet port <NUM>.

A proper amount of oil is introduced from an oil tank (not shown) into the outer casing <NUM> for acting as coolant and lubricating fluid. In the example shown in <FIG>, for instance, the inner casing <NUM> is immersed in an oil bath <NUM>.

In order to drive the rotor <NUM> of the vacuum pump, the vacuum pumping system <NUM> further comprises a motor <NUM> and the pump rotor <NUM> is mounted to a rotation shaft which is driven by said motor.

The motor <NUM> generally is an electric motor comprising a stationary stator and a rotating rotor cooperating with each other and an output shaft connected to the motor rotor: according to a first possible arrangement, the output shaft of the motor rotor is connected to the rotation shaft of the pump rotor by a mechanical or magnetic coupling for driving the pump rotor in rotation; according to a second, alternative arrangement, the output shaft of the rotor motor can be integral with the rotation shaft of the pump rotor, so as to drive the pump rotor in rotation.

A vacuum pumping system as shown in <FIG> is disclosed, for instance, in <CIT> by the same Applicant.

Known vacuum pumping systems of the kind disclosed above have several drawbacks.

First of all, it has to be considered that, during operation of the vacuum pump, the motor may be at atmospheric pressure, while the pumping chamber of the vacuum pump receiving the pump rotor may be at sub-atmospheric pressure. Therefore, a dynamic seal is to be provided between the output shaft of the motor rotor and the rotation shaft of the pump rotor.

Dynamic seals are more expensive and less reliable than static seals and a failure of the dynamic seals can involve malfunctioning of the vacuum pump and damages to the vacuum pump and to the vacuum chamber connected thereto. Moreover, in the case of vacuum pumping systems comprising a rotary vane vacuum pump, these dynamic seals are the main cause of oil leaks during operation of the pump.

Secondly, a vacuum pumping system comprising a vacuum pump and its juxtaposed motor is bulky and heavy, which represents a severe drawback during shipping of the vacuum pumping system and installation thereof, especially in those applications in which little room is available.

Moreover, if the motor is cantilevered on the vacuum pump (as shown in <FIG>), the output shaft of the motor rotor and the rotation shaft of the pump rotor are subjected to flexure stresses, which increase as the size and weight of the vacuum pump and of the motor increase.

<CIT> discloses a gear pump which sucks a fluid from a fluid reservoir or fluid source and drive it to a desired component or device. Such gear pump includes a sealed casing including a pump body and a cover, which define between them a cavity in fluid communication with a suction area and a discharge area; two meshing gear wheels are housed in the cavity for pumping the fluid from the fluid reservoir or fluid source to the desired component or device; first and second inner electromagnetic assemblies that actuate the rotation of the gear wheels are also housed in the cavity.

<CIT> discloses an electric pump unit comprising, on the one hand, an electric motor stator and an electric motor rotor, and, on the other hand, a pumping stator and a pumping rotor. The pumping stator is arranged concentrically inside the motor stator and the pumping rotor is obtained by the motor rotor, said motor rotor having an axis of rotation eccentric inside the enclosure formed by the pumping stator.

<CIT> discloses a vacuum pump designed as a mono-vane cell pump, comprising a stator ring with windings, a rotor and a vane which divides a working chamber formed between the stator and a rotor into working cells having different volumes. Inside the stator ring, a magnetic ring with a running ring, on which the vane is securely connected on one side, is rotationally mounted with respect to the rotor. A stator ring with windings surrounds the magnetic ring radially on the outside and is suitably controlled by a control device in order to drive the magnetic ring to rotate.

<CIT> discloses a vacuum-pumping device comprising a vacuum pump body, a rotary shaft, a vacuum pump rotor, a motor stator and a motor rotor, wherein the device body is equipped with a gas inlet, a gas exhaust hole, an oil storage cavity and a motor bin. The vacuum pump rotor is fixedly mounted on the rotary shaft, and defines a vacuum pump stator cavity with the inner wall of the vacuum pump body; the motor stator and the motor rotor are mounted in the motor bin; the motor stator is fixedly connected to the vacuum pump body; and the motor rotor is fixedly connected with the rotary shaft.

It is therefore an object of the present invention to overcome the above-mentioned drawbacks of prior art, by providing a more reliable vacuum pumping system, in which the need for dynamic seals is avoided.

It is a further object of the present to provide a vacuum pumping system which is lighter and more compact than vacuum pumping systems according to prior art.

The above and other objects are achieved by means of a vacuum pumping system as claimed in the appended claims.

According to embodiments of the invention, the motor stator and the motor rotor are received in the pumping chamber of the vacuum pump.

Preferably, the motor stator and the motor rotor, as well as the pump stator and the pump rotor, are entirely received in said pumping chamber.

In the context of this description, the term "pumping chamber" can be understood as the space inside the pump housing, which is defined by the pump stator and in which the pump rotor is received and carries out the pumping action by cooperating with the pump stator. During operation of the vacuum pump the pressure within the pumping chamber is typically not constant and/or equal to the atmospheric pressure; on the contrary, it varies between a minimum value lower than the atmospheric pressure and a maximum value greater than the atmospheric pressure during expansion and compression phases of the pumping action of the pump rotor and stator.

According to embodiments of the invention, during operation of the pump, the motor stator and the motor are substantially at the same pressure as the pump stator and the pump rotor. As the motor stator and the motor are substantially at the same pressure as the pump stator and the pump rotor, the vacuum pumping system according to embodiments of the invention can be made as a single, sealed unit and no dynamic seal between the vacuum pump and its motor is needed.

Even if static seals are provided in the vacuum pumping system (for instance, for electric connections), static seals are cheaper than dynamic seals and, most importantly, are no subjected to fatigue, so that there is no risk of deterioration and failure of these static seals due to fatigue.

According to a preferred embodiment of the invention, the pump rotor is at least partially made as a hollow body and the motor is received inside the pump rotor.

Preferably, said pump rotor is completely made as a hollow body, more particularly as a hollow cylinder.

According to this preferred embodiment, the motor rotor is fastened to or integral with the inner surface of the cavity provided in the pump rotor and the motor stator is located inside said cavity.

According to a particularly preferred embodiment of the invention, the motor rotor comprises one or more permanent magnets fastened to or integral with the inner surface of the cavity of the pump rotor and the motor stator is arranged inside said cavity and comprises a body made of a ferromagnetic material and carrying one or more corresponding windings. The aforesaid preferred embodiment of the invention involves several additional advantages.

The vacuum pumping system can be made compact and light, which is particularly advantageous during shipping and installation of the vacuum pumping system.

During rotation of the pump rotor, the pump rotor can be suspended inside the pumping chamber, which allows to reduce the power absorbed by the pump; moreover, due to the fact that the pump rotor can be suspended inside pumping chamber, the noise generated by the vacuum pump may be reduced and vibrations generated by the vacuum pump may be also reduced, which may increase working life and reliability of the pump itself.

According to a preferred embodiment of the invention, the pump rotor can be concentrically driven with respect to the longitudinal axis of the motor stator arranged in the cavity of said pump rotor.

According to another preferred embodiment of the invention, the pump rotor can be eccentrically driven with respect to the longitudinal axis of the motor stator arranged in the cavity of said pump rotor.

The invention can be implemented in several different vacuum pumping systems, comprising different kinds of vacuum pumps.

The invention can be implemented in a vacuum pumping system including a rotary vane vacuum pump.

Further features and advantages of the present invention will become more evident from the detailed description of a preferred embodiment of the invention, given by way of non-limiting example, with reference to the accompanying drawings, in which:.

In the following, a preferred embodiment of the invention will be described in detail with reference by way of non-limiting example to a vacuum pumping system comprising a rotary vane vacuum pump.

Referring to <FIG>, a vacuum pumping system <NUM> comprising a rotary vane pump <NUM> and its motor <NUM> is shown.

In a manner known per se, the rotary vane vacuum pump <NUM> comprises a pump housing <NUM>, in which a pump inlet <NUM> and a pump outlet <NUM> are provided and which receives pumping elements for pumping a gas from said pump inlet to said pump outlet.

In the shown embodiment, the pumping elements comprise a stationary pump stator <NUM> and a rotatable rotor <NUM>.

The pump housing <NUM> receives the stationary pump stator <NUM> which surrounds and defines a pumping chamber <NUM> (which has a cylindrical shape in the shown embodiment), which is connection with the pump inlet <NUM> and the pump outlet <NUM>. The pumping chamber <NUM> accommodates a rotatable cylindrical rotor <NUM>, which is eccentrically located with respect to the axis of said cylindrical pumping chamber. One or more radially movable radial vanes <NUM> (three in the example shown in <FIG>) are mounted on said pump rotor <NUM> and are kept against the wall of the pumping chamber <NUM> either by means of corresponding springs (not shown) or by the centrifugal force.

When the vacuum pump is running, gas is sucked from a vacuum chamber (not shown) to be evacuated through the pump inlet <NUM> of the pump and passes through an inlet duct <NUM> into the pumping chamber <NUM> where it is pushed and thus compressed by the vanes <NUM>, and then it is exhausted through an exhaust duct <NUM> ending at the pump outlet <NUM>.

Oil is introduced from an oil tank <NUM> connected to the vacuum pump <NUM>, so that the pump housing <NUM> is immersed in an oil bath, which acts as coolant and lubricating fluid.

The vacuum pumping system <NUM> further comprises a motor <NUM> for driving in rotation the pump rotor <NUM>.

According to embodiments of the invention, the motor <NUM> is located in the pumping chamber <NUM> of the vacuum pump <NUM>.

As the motor rotor <NUM> and the motor stator <NUM> are located in the pumping chamber <NUM>, said motor rotor <NUM> and said motor stator <NUM> always are at substantially the same pressure conditions as the pump stator <NUM> and the pump rotor <NUM> during operation of the pump.

In order to receive the motor in the pumping chamber <NUM>, in the disclosed preferred embodiment, the pump rotor <NUM> is made, at least in part, as a hollow body, so that a cavity <NUM> is defined within the body of said pump rotor and the motor <NUM> is at least partially, and preferably entirely, received within said cavity <NUM>.

More particularly, a cylindrical cavity <NUM> is defined in the cylindrical pump rotor <NUM>, which cavity is parallel to and concentric with the body of said pump rotor, and the motor <NUM> is received within said cylindrical cavity <NUM>.

In the shown embodiment, the cavity <NUM> extends over the whole axial length of the pump rotor <NUM>, so that said pump rotor has the overall shape of a hollow cylinder. However, in alternative embodiments, the cavity <NUM> could extend over a portion only of the axial length of the pump rotor <NUM>.

In the shown embodiment, the motor is a permanent magnet motor and the motor rotor comprises a plurality of permanent magnets <NUM> which are fixed to the inner surface of the cavity <NUM> of the pump rotor <NUM>.

As the permanent magnets of the motor rotor are fixed to the inner surface of the cavity of the pump rotor, the motor rotor <NUM> and the pump rotor <NUM> together form a single rotor unit. These permanents magnets are shaped as slightly curved, rectangular slabs <NUM>, arranged substantially parallel to the longitudinal axis of the pump rotor <NUM> and extending over a substantial portion of the axial length of the cavity <NUM>, said slabs <NUM> being equally spaced along the inner wall of the cavity <NUM> in the circumferential direction.

Said slabs <NUM> preferably are even in number and they are arranged so that the polarity of each slab is opposite to the polarity of the adjacent slabs.

It will be evident to the person skilled in the art that the motor rotor <NUM> could also be made with a different shape. For instance, such motor rotor could be made as a cylindrical sleeve fitted into the cavity <NUM> of the pump rotor <NUM>. Furthermore, the motor rotor could be made integral with the inner surface of the cavity <NUM> of the pump rotor. Even in these alternative embodiments, the motor rotor <NUM> and the pump rotor <NUM> together form a single rotor unit.

The motor stator <NUM> is located inside the cavity <NUM> of the pump rotor <NUM> is fastened to or integral with the pump housing <NUM> and/or the pump stator <NUM>. Said motor stator comprises a body made of ferromagnetic material (such as, ferrite, SMC materials and the like), having substantially the same axial length as the permanent magnets <NUM> and provided with a plurality of radial arms <NUM> carrying respective windings (not shown).

In the shown embodiment, the motor stator is made as a generally cylindrical body arranged parallel to and concentric with the cylindrical cavity <NUM>. In other word, the air gap between the motor stator <NUM> and the motor rotor <NUM> has a constant width along the circumference of said motor stator and rotor <NUM>, <NUM>. Accordingly, in the shown embodiment, the motor rotor <NUM> and the pump rotor <NUM> are concentrically driven with respect to the longitudinal axis of said motor stator (i.e. to the longitudinal axis of the cavity <NUM>).

However, in alternative embodiments of the invention, it is possible that the motor stator is made as a cylindrical body arranged parallel to the cylindrical cavity <NUM> but in an eccentric position with respect to the longitudinal axis of said cavity. In other word, the air gap between the motor stator <NUM> and the motor rotor <NUM> has a width at each point along the circumference of said motor stator and rotor <NUM>, <NUM> which is variable over time. Accordingly, in such embodiments, the motor rotor <NUM> and the pump rotor <NUM> would be eccentrically driven with respect to the longitudinal axis of said motor stator (i.e. to the longitudinal axis of the cavity <NUM>) and the axis of the motor rotor <NUM> (and of the pump rotor <NUM>) moves following a circular or elliptical trajectory.

It is evident from the above, that the arrangement according to embodiments of the invention allows to avoid the need for dynamic seals between the vacuum pump and the motor, since the motor <NUM> is located in in the pumping chamber <NUM> of the vacuum pump, as the pump stator and rotor <NUM>, <NUM>.

While in vacuum pumping systems according to prior art the motor typically is at atmospheric pressure during operation of the vacuum pump, in the pumping system according to embodiments of the invention the motor stator <NUM> and the motor rotor <NUM> always are at the same pressure as the pump stator <NUM> and the pump rotor <NUM> during operation of the pump.

It is evident from the above that, due to the absence of dynamic seals, the vacuum pumping system according to embodiments of the invention is more reliable. In case of applications to vacuum pumping systems including a rotary vane vacuum pump, leaks of oil through the dynamic seals are prevented.

It is also evident from the above that the arrangement according to embodiments of the invention allows to obtain a very compact design, as well as a vacuum pumping system formed by fewer components and lighter than those of prior art.

It will be further evident from the above that, thanks to the cooperation of the motor stator <NUM> and the motor rotor <NUM>, during rotation of the pump rotor <NUM>, said pump rotor <NUM> is magnetically suspended without contact inside the pumping chamber <NUM>, which involves a remarkable reduction of the noise generated by the vacuum pump as well as of the vibrations generated by the vacuum pump, thus increasing the working life and reliability of the vacuum pumping system.

The vacuum pump <NUM> is closed at both its axial ends and the pump rotor <NUM> can be provided, at both its axial ends, with bushings (not shown), interposed between said pump rotor and the pump housing <NUM>, which in turn is provided with seats for receiving said bushings. Due to the fact that the pump rotor <NUM> is suspended during operation of the pump, there is no contact on the bushings and such absence of contact advantageously involves a reduction in the power absorbed by the pump.

With reference now to <FIG> and <FIG>, a second embodiment of the invention is shown. This second embodiment of the invention is almost identical to the first embodiment disclosed above and the same numerals used in <FIG> are also used in <FIG> for denoting identical or similar parts of the vacuum pumping system.

This second embodiment differs from the first embodiment in that the motor stator is provided with one or more longitudinal through-hole(s) <NUM> (only one, centrally arranged through-hole in the example shown in <FIG>) accommodating respective pipe(s) <NUM>.

The pipe <NUM> extends through the motor stator <NUM> and projects into the adjacent oil tank <NUM>, ending with a mouth <NUM> which is always below the level of oil in the oil tank <NUM> during operation of the vacuum pumping system <NUM>.

At the cold start of a rotary vane vacuum pump, the required torque may be very high, mainly because of the oil viscosity that is strongly dependent on the temperature and is very high at low temperature.

The pipe <NUM> can be advantageously used for transferring heat from the motor stator <NUM> to the oil bath <NUM> before starting the pump, so as to increase the oil temperature and reduce its viscosity.

More in detail, at the cold start of the vacuum pumping system <NUM>, the windings of the motor stator <NUM> can be energized while keeping the motor rotor stationary. In such conditions, the power delivered to the motor stator is not used for making the motor rotor rotate, but it is dissipated as heat, thus leading to an increase of the motor stator temperature.

This heat can be transferred from the motor stator <NUM> to the oil tank <NUM> thanks to the pipe <NUM>, which to this purpose is preferably made of a material having a high thermal conductivity.

When the motor rotor is successively made to rotate, the oil viscosity will be decreased and the required torque will be correspondingly reduced.

Another advantage of this second embodiment is that the pipe <NUM> can be further exploited for cooling the vacuum pump during operation.

In fact, during operation of the vacuum pump, oil is sucked from the oil tank <NUM> through the pipe <NUM> and into the vacuum pump <NUM>. To this purpose, the pipe <NUM> is provided with radial orifices <NUM> at both axial ends of the motor stator <NUM>.

This arrangement turns out to be particularly effective, as the oil is introduced in the vacuum pump close to the longitudinal axis of the pump itself.

It is evident that the above disclosure has been given by way of non-limiting example and that several variants and modifications within the reach of the person skilled in the art are possible, without departing from the scope of the invention as defined by the appended claims.

Claim 1:
Vacuum pumping system (<NUM>) comprising:
- a rotary vane vacuum pump (<NUM>), comprising a pump housing (<NUM>) in which a pump inlet (<NUM>) and a pump outlet (<NUM>) are defined and in which a stationary pump stator (<NUM>) is received, said pump stator (<NUM>) defining a pumping chamber (<NUM>) in which a pump rotor (<NUM>) is arranged, said pump stator and said pump rotor cooperating with each other for pumping a gas from said pump inlet to said pump outlet;
- a motor (<NUM>), which comprises a motor stator (<NUM>) and a motor rotor (<NUM>), said motor stator and said motor rotor cooperating with each other for driving in rotation said pump rotor (<NUM>);
characterized in that said motor rotor (<NUM>) and said motor stator (<NUM>) are received in said pumping chamber (<NUM>) of said rotary vane vacuum pump.