DESCRIPTION

Field of application

The present invention is generally applicable to the technical field of electric motors. In particular, the object of the invention is a modular electric motor kit for producing an electric motor in different versions.

State of the Art

As it is known, an electric motor is generally constituted from a motor casing that houses and supports a stator and a rotor, the rotor being rotatably associated to the motor casing through a motor shaft mounted on roll bearings. The stator and the rotor, it conveniently supplied by an electric voltage, mutually cooperate to generate a torque on the motor shaft.

The motor casing has a structural function and is generally made in metal, through molding and subsequent machining of the thereby obtained molded part. A particular used metal is aluminum, due to its lightness, small cost and ease of machining, that allow to obtain an electric motor with limited cost.

On the other hand, aluminum has the drawback of being unsuited to be used in particular circumstances, for example in chemically aggressive environments, or in food processing plants. In the latter cases, it is known making the motor casing in materials that are corrosion-resistant or suited to be used with food, among which stainless steel is particularly known, e.g. AISI 304 or AISI 316.

According to a known technique, stainless-steel motor casings are made in a similar way as aluminum casings, i.e. through molding and subsequent machining of the thereby obtained molded part. However, due to the limited machinability of stainless steel compared to aluminum, and to the higher cost of the material, the stainless-steel motor casings have the drawback to be much more expensive compared to equivalent motor casings made in aluminum. The above drawback is particularly emphasized with AISI 316.

In order to reduce the costs of the electric motor with stainless-steel housing, it is common practice to buy the housings, or the corresponding electric motors, in countries where labor cost is limited. However, such production mode has the drawback that it requires quite a long supply time, with the consequent need to create a sufficiently big stock to quickly satisfy customer requests, hence generating a correspondingly high cost due to the immobilization of capital.

Summary of the invention

The present invention aims at overcome at least partially the above mentioned drawbacks of the known art.

In particular, it is an aim of the invention to propose an electric motor equivalent to a motor of known type having a motor casing in a given material, but whose production has a substantially lower cost.

It is also an aim of the invention that at least a part of the components of the said electric motor can be used to make an electric motor of a second type, equivalent to a motor of known type having a motor casing in a material different from the previous one.

The above aims are reached by an electric motor kit according to the main claim.

Further detail features of the invention are specified in the corresponding dependent claims.

The above aims are also reached by an electric motor comprising the above kit, according to claim 16.

The above aims are also reached by a method to adapt an electric motor to the use in two different operating environments, according to claim 17.

According to a first aspect, the invention concerns a modular electric motor kit, comprising a motor cartridge provided with a motor casing having structural function to house and support a stator and a rotor. The motor casing comprises a tubular body in a first material, at whose ends two corresponding inner covers are associated to rotatably support the rotor. The electric motor kit further comprises a shell to house the said motor cartridge, the shell comprising a tubular sleeve in a second material that is different from the first material, the tubular sleeve being configured to cover the tubular body.

Advantageously, the electric motor kit of the invention allows to make a first type of electric motor that is equivalent to an electric motor of known type having a motor casing entirely made in a second material relatively expensive, but whose housing is at least partly made in a first material that is relatively less expensive.

As an example, the first material can be aluminum and the second material can be stainless steel, e.g. AISI 304 or AISI 316.

At the same time, the motor cartridge can be used to make an electric motor of a second type equivalent to electric motors of known type provided with a motor casing entirely made in the first material.

Therefore, advantageously, a manufacturer can make both types of motor as above mentioned, while reducing the overall value of the immobilized stock compared to that related to a stock of known-type electric motors equivalent to the two above mentioned types. In fact, the manufacturer can reduce the stock to a given number of the above motor cartridges, each having a cost that is comparable to that of a motor of known type having a casing entirely made in the first material, together with a given number of shells, whose cost is substantially lower than that of known- type motors having casings entirely made in the second material.

The above mentioned reduction in costs also renders economically feasible for the manufacturer to reduce the manufacturing supply chain, for example by making the shell internally, or by buying it by a supplier located at a short distance, so as to avoid the higher supply times that are typical of the long manufacturing supply chains.

Still advantageously, the possibility to use the same motor cartridge to make electric motors of both above mentioned types allows to more flexibly and rapidly fulfill the customers' orders.

Still advantageously, the provision of the above shell allows to transform an electric motor of the second type, even already installed, in an electric motor of the first type, thus bringing evident advantages from the point of view of cost and timing for both motor manufacturer and customer.

According to a second aspect of the invention, the tubular body and the tubular sleeve are mutually coupled in such a way as to obtain a configuration of mutual heat conduction.

Advantageously, the condition just mentioned, together with the possibility to make the tubular sleeve with a small thickness thanks to its non-structural function, allow to avoid using auxiliary devices for forced cooling to compensate for the smaller thermal-dissipation capacity of the electric motors of the above mentioned first type.

The above aim and advantages, together with other that will be mentioned in hereinafter, will be more apparent from the following description of some preferred embodiments of the invention, that are disclosed as non-limiting examples with the help of the attached drawings.

Brief description of the drawings

Fig. 1 shows the electric motor kit of the invention, in partially exploded axonometric view.

Fig. 2 shows the electric motor kit of Fig. 1 , in assembled configuration, in lateral sectioned view.

Figs. 3 and 4 show corresponding magnified views of details A and B of Fig. 2.

Fig. 5 shows a component of the electric motor kit of Fig. 1 , in axonometric view.

Fig. 6 shows an electric motor using the electric motor kit of the invention, in lateral sectioned view.

Figs. 7 and 8 show corresponding magnified views of details C and D of Fig. 6.

Fig. 9 partially shows a variant embodiment of the electric motor kit of the invention, in exploded view.

Detailed description of some preferred embodiments

The electric motor kit of the invention, referred to in the cross-section of Fig. 2 on the whole as 24, comprises a motor cartridge 1 , shown in Fig. 5 and that, in turn, comprises a motor casing 2 that externally delimits a first containment volume 3 to house a stator unit 21.

In particular, the motor casing 2 comprises a tubular body 4 developing according to a first longitudinal axis X, and made in a first material that might be, for example, aluminum or another material having similar properties as aluminum.

Preferably, the tubular body 4 is arranged in contact with the stator unit 21 so that the heat produced by the stator unit 21 can be dissipated, by heat conduction, towards the outside of the motor casing 2. Still preferably, the contact between tubular body 4 and tubular sleeve 11 is mediated by a fluid layer to maximize the contact surface. Preferably, the above fluid layer has lubricant properties to, advantageously, facilitate coupling the above two components when assembling the electric motor 20 by sliding the tubular sleeve 11 on the tubular body 4.

In the other hand, in variant embodiments of the invention, the two said components 4, 11 might be arranged in direct mutual contact, without the mediation of any fluid layer.

The tubular body 4 defines an outer surface 4a whose transverse cross- section, taken perpendicularly to the longitudinal axis X, is preferably uniform along the longitudinal axis X itself and, still more preferably, has a circular shape.

The motor casing 2 further comprises two inner covers 5 and 6 arranged in contact, respectively, with the ends 4b, 4c of the tubular body 4 that are mutually opposite according to the first longitudinal axis X. A first inner cover 5 comprises a corresponding through hole 7 that is coaxial to the first longitudinal axis X.

The motor cartridge 1 further comprises a motor shaft 8 arranged in the first containment volume 3, that is rotatably associated to each one of the two inner covers 5 and 6 preferably through two bearings 23 housed in two housings 5a, 6a belonging to, respectively, the two inner covers 5, 6. The motor shaft 8 supports a rotor unit 22 that electromagnetically cooperates with the above stator unit 21 to generate a torque on the motor shaft 8. Moreover, a first end 8a of the motor shaft 8 is arranged projecting through the through hole 7 of the first inner cover 5 so as to allow its connection with an external device, not shown in the drawings, to which the above torque is transmitted. Still preferably, the end of the motor shaft 8 opposite to the first end 8a is arranged projecting through a through hole of the second inner cover 6.

It is understood that the motor cartridge 1 above described, provided with motor casing 2, stator and rotor units 21, 22, and motor shaft 8, constitutes an electric motor in all respects.

The electric motor kit 24 also comprises a shell 9 that externally delimits a second containment volume 10 to house the motor cartridge 1 in an operating configuration.

In particular, the shell 9 comprises a tubular sleeve 11 made in a second material different from the first material of the tubular body 4, for example stainless steel or another material having similar properties. The tubular sleeve 11 develops according to a second longitudinal axis Y that, in the above operating configuration, coincides with the first longitudinal axis X. The tubular sleeve 11 defines an inner surface 11a and is configured so that, when the motor cartridge 1 is housed in the second containment volume 10 in the above operating configuration, the tubular sleeve 11 extends at least along the same portion of the first longitudinal axis X along which the tubular body 4 extends, so as to cover the outer surface 4a of the tubular body 4.

The possibility to cover the tubular body 4 with the tubular sleeve 11 prevents the outer surface 4a made in the first material from being exposed to the external environment, while exposing the tubular sleeve 11 made in the second material instead.

Therefore, it is reached the aim of making an electric motor 20 provided with a motor casing whose superficial properties are equivalent to those of a known-type electric motor with a motor casing entirely made in the above second material, but in which the second material is present only in the tubular sleeve 11 , while the tubular body 4 is made in the first material.

At the same time, in those implementations that do not require having a motor casing whose outer surface is made in the second material, it is sufficient to use the motor cartridge 1 without the tubular sleeve 11. It may thus be understood that the above kit 24 advantageously allows a motor manufacturer to limit the cost of the stock, because it allows to make two types of electric motor - i.e. whose surfaces are made in the first material and in the second material, respectively - by using the motor cartridge 1 as a base for both types and by merely adding, in one of the two types, the shell 9 in the second material. Therefore, it will be sufficient for the motor manufacturer to keep a stock of a certain number of motor cartridges 1 and shells 9, rather than keeping two different types of electric motors.

Preferably, in the above operating configuration, the inner surface 11a of the tubular sleeve 11 is in contact with the outer surface 4a of the tubular body 4 in order to obtain a condition of mutual thermal-conduction with the tubular body 4. Preferably, the inner surface 11a can be conjugated with the outer surface 4a so that, when the motor cartridge 1 is housed in the second containment volume 10, the outer surface 4a is completely, for the most part, in contact with the inner surface 11a in order to achieve a good thermal conductivity between the two components.

Preferably, the inner surface 11a is configured to be coupled to the outer surface 4a through a sliding movement of the tubular sleeve 11 with respect to the tubular body 4 according to the direction of the first longitudinal axis X, as schematically shown in the exploded view of Fig. 1 , which advantageously renders the coupling easier. Still more preferably, the cross section of the inner surface 11a transversely to the second longitudinal axis Y is uniform along the second longitudinal axis Y and, even more preferably, is cylindrical.

As anticipated above, preferably the first material is aluminum and the second material is stainless steel, e.g. AISI 304 or AISI 316. That, advantageously, allows to make an electric motor 20 whose superficial properties are equivalent to those of a known-type electric motor having a casing entirely made in stainless steel, yet noticeably cheaper than the latter, because a substantial portion of its casing - in particular, the tubular body 4 - is made in aluminum.

The tubular sleeve 11 might not necessarily have a structural function. On the contrary, it is preferable that such structural function be performed by the tubular body 4, by conferring it a suitable thickness. As a consequence, the motor cartridge 1 might be used also to make a motor having a casing entirely made in the first material, thus avoiding the need to coat the tubular body 4.

The use of a tubular sleeve 11 having reduced thickness also allows to facilitate the dissipation of heat generated by the electric motor 20 during operating conditions. As an example, the tubular sleeve 11 might have the minimum thickness allowed by the known techniques. Advantageously, a tubular sleeve 11 having reduced thickness might be obtained, for example, from a metallic sheet, in which case the tubular sleeve 11 might have a thickness equal to the minimum thickness of the commercially available sheets. In case of stainless steel, that minimum thickness is very limited, and can be even less than 0.5 mm. Still advantageously, the process to obtain the tubular sleeve 11 from metallic sheet is relatively cheap and allows to limit material scraps. In fact, the process requires simple operations such as calendering and, possibly, subsequent welding of the sheet, instead of the machining operations through which the known-type motor casings are commonly obtained, particularly for those casings made in stainless steel.

The applicant noticed that the manufacturing of the tubular body 4 and the tubular sleeve 11 as above disclosed makes it possible to obtain such a good heat conduction between the tubular body 4 and the tubular sleeve 11 that, in normal operating conditions, allows to dissipate the heat generated by the electric motor 20 to an extent that is sufficient to prevent overheating of the electric motor 20, hence avoiding the need to provide any forced cooling device, such as a fan.

Clearly, other combinations of the first material and second material are possible that, despite being different from the one above mentioned, bring similar advantages.

Preferably, the tubular sleeve 11 is configured in such a way that, in operating configuration, it covers also portions of the two inner covers 5, 6 possibly projecting with respect to the tubular body 4 according to the direction of the first longitudinal axis X. Generally, the above projecting portions are provided in order that the two ends 4b, 4c of the tubular body 4 can be used as references to position the inner covers 5, 6, as can be noticed from details of Figs. 3 and 4. To that end, the inner covers 5, 6 are provided with corresponding mutually faced housings 5b, 6b that receive the above ends 4b, 4c. The inner covers 5, 6 can be mutually coupled, for example through using tie-rods 25, one of which can be seen in Fig. 2, so as to also constrain the tubular body 4.

Preferably, the shell 9 further comprises two first outer covers 12, 13 made in the second material, and that can be arranged in contact with, respectively, two ends 11b, 11 c of the tubular sleeve 11, the ends 11b, 11c being opposite according to the second longitudinal axis Y and delimiting the second containment volume 10 along the direction of the second longitudinal axis Y.

The above two first outer covers 12, 13 are configured so that they cover at least partially the two inner covers 5, 6, in such a way that will be apparent hereinafter. As a consequence, the two inner covers 5, 6 can be made in the first material in order to limit, or avoiding, the use of the second material for the motor casing 2, in such a way as to enhance the above mentioned advantages.

Preferably, the two first outer covers 12, 13 comprise two corresponding reference surfaces 12a, 13a that, when the motor cartridge 1 is housed in the second containment volume 10, project with respect to the tubular body 4 and the inner covers 5, 6 in a direction that is orthogonal to the first longitudinal axis X, and that are mutually faced so as to be arranged in contact with two respective ends 11b, 11c of the tubular sleeve 11 in order to constrain the tubular sleeve 11 to the two first covers 12, 13

Preferably, and as can be noticed in Figs. 3 and 4, the above mentioned reference surfaces 12a, 13a are defined by corresponding recesses belonging to the first outer covers 12, 13.

Still preferably, the first outer covers 12, 13 and the tubular sleeve 11 are configured in such a way that, when they are mutually associated as above disclosed, they define a surface that is substantially smooth and without corners, to the advantage to facilitate cleaning the motor and avoid accumulation of dirt. What just disclosed might be obtained, for example, by making the above mentioned components so that the corresponding outer surfaces develop around the second longitudinal axis Y in circular shapes and with mutually equal diameters.

Still preferably, when the motor cartridge 1 is housed in the second containment volume 10, the shell 9 is constrained to the motor casing 2 through the two first outer covers 12, 13, each one of which is secured to a corresponding inner cover 5, 6 through connection elements 14, for example the screws 14a that are shown in particular in Figs. 1 and 2, screwed to corresponding threaded holes 14b provided on the inner covers 5, 6. Preferably, the first outer covers 12, 13 are arranged in contact, respectively, with the inner covers 5, 6, as shown in particular in Figs. 3 and 4.

Preferably, a first one of the above mentioned first outer covers, that is referred to in the drawings as 12, acts as a connection flange to connect the motor cartridge 1 to the external device receiving the torque from the motor shaft 8. To that end, the first outer cover 12 comprises threaded holes 16, one of which can be seen e.g. in Fig. 2, to securing the electric motor 20 to the external device. The above mentioned first outer cover 12 also comprises a corresponding through hole 15 to house the first end 8a of the motor shaft 8 in a position that projects outwardly from the second containment volume 10 when the motor cartridge 1 is housed in the second containment volume 10, so as to allow connecting the motor shaft 8 to a corresponding driven shaft belonging to the external device.

Clearly, it is possible to provide a plurality of first outer covers 12 having mutually different shapes, that might be chosen e.g. among those defined in the reference technical standards concerning the coupling flanges. That allows to obtain a corresponding plurality of electric motors 20, each one of which is suited to be coupled to a different external device.

With regard to the first outer cover 13, that is secured to the motor cartridge 1 , it might act as a support for auxiliary components referred to in Fig. 2 as 29, and that, purely by way of example, might comprise cable glands to house a cable for power supply, power supply connectors, and whatever else. Moreover, the first outer cover 13 might also perform a sealing function to prevent liquids from entering the motor casing 2, as it will be disclosed in greater detail hereinafter.

Preferably and as can be seen in Fig. 6, kit 24 further comprises two second outer covers 26, 27 that can be secured to the motor casing 2 in place of, respectively, the two above mentioned first outer covers 12, 13, but that are made in the first material. Preferably, each one of the above two second outer covers 26, 27 is secured to a corresponding inner cover 5, 6, preferably through connection elements 14 similar to those used to secure the first outer covers 12, 13, so as to be interchangeable with them.

Preferably, the second outer covers 26, 27 perform the same functions of the first outer covers 12, 13.

In particular, a first one of the second outer covers, which replaces the corresponding first outer cover 12 and which is referred to in the drawing as 26, might perform the function of connection flange to connect with the external device. In the latter case, cover 26 is provided with threaded holes 16 and through hole 15 similar to the respective holes in the first outer cover 12. Clearly, the second outer cover 26 might be made in a plurality of mutually different shapes, each one of which is intended to replace a corresponding shape of the first outer cover 12.

Similarly, the other second outer cover 27 might perform the same support functions of the auxiliary components 29, as well as liquid-tight functions performed by the corresponding first outer cover 13.

Advantageously, the provision of the above mentioned second outer covers 26, 27 allows to make a second electric motor 28 that is dimensionally interchangeable with the above disclosed first electric motor 20, yet having a different outer surface's material, which is made in the first material instead of in the second material. In particular, since the tubular body 4 has a structural function and is made in the first material, it might as well perform the function of an outer shell, similar to that of the shell 9 of the first electric motor 20. Advantageously, the configuration just disclosed avoids the need to use a tubular sleeve 11 of the kind used in the first electric motor 20.

In that case, differently from the first electric motor 20, the portion of the motor casing 2 corresponding to the outer surface 4a of the tubular body 4 remains exposed to the outside during the use of the second electric motor 28.

In the lacking of a tubular sleeve, the two second outer covers 26, 27 may have dimensions in a direction orthogonal to the first longitudinal axis X smaller than those of the first outer covers 12, 13, because in this case there is no need to provide projecting reference surfaces similar to those previously disclosed to constrain the tubular sleeve 11.

Preferably, and as can be seen in detail in Figs. 7 and 8, the said dimensions correspond to those of the tubular body 4 and of the first inner covers 5, 6, so that the outer surface of the second electric motor 28 be substantially smooth and without corners, in order to facilitate cleaning the motor.

In other respects, the second outer covers 26, 27 might have geometries that are substantially identical, or different, to those of the corresponding first outer covers 12, 13, as long as they are capable to perform similar functions and replace them.

Preferably, the electric motor kit 24 further comprises a sealing assembly 17 to prevent liquids from entering the motor casing 2 from the outside.

Preferably, the above mentioned sealing assembly 17 comprises first liquid- tight elements 18, that can be seen e.g. in Figs. 2, 4, 6 and 8, that are interposed between the tubular body 4 and each inner cover 5, 6 as well as, preferably, between the through hole 7 of the inner cover 5 and the motor shaft 8. Advantageously, the first liquid-tight elements 18 belong to the motor cartridge 1 , hence preventing, or limiting, the need for providing further liquid-tight elements outside of the motor cartridge, in order to facilitate assembling the electric motors 20 and 28. Preferably, the first liquid-tight elements 18 comprise gaskets, e.g. O-ring, V-ring, and whatever else.

Still preferably, the sealing assembly 17 comprises second liquid-tight elements arranged between the tubular sleeve 11 and the tubular body 4 to, advantageously, prevent liquid from coming into contact with the tubular body 4. The above mentioned second liquid-tight elements preferably comprise the previously mentioned fluid layer, interposed between the tubular sleeve 11 and the tubular body 4. However, in a variant embodiment, the second liquid-tight elements might comprise a direct contact between the above elements and/or gaskets.

Still preferably, and as can be seen in the Figures from 2 to 8, the sealing assembly 17 comprises third liquid-tight elements 19 that can be interposed between each inner cover 5, 6 and a corresponding first outer cover 12, 13, or second outer cover 26, 27. Advantageously, the third liquid-tight elements 19 prevent liquid from coming into contact with the inner covers 5, 6 and, more generally, entering gaps that might be present between the inner covers 5, 6 and the outer covers 12, 13, 26, 27, in which there might be some components that must be prevented from coming into contact with liquids. Third liquid-tight elements 19 can as well prevent liquids from entering the motor cartridge 1 through a through hole of the inner cover 6 that might possibly house the shaft 8, as seen in Figs. 2 and 6. Third liquid-tight elements 19 might be of a kind similar to the first liquid-tight elements 18.

A variant embodiment of the electric motor kit 24 is shown in Fig. 9 where, for the sake of simplicity, the same numerals are used for elements that are equivalent to those of the kit of Fig. 1.

The above mentioned variant embodiment differs from that of Fig. 1 for the addition of an angular position sensor 30 suited to determine the angular position of the motor shaft 8. The first inner cover 5 is provided with a recess 31 to house the sensor 30. Consequently, advantageously, it is possible to insert the sensor 30 only when required, in a simple way and without the need to change kit 24. In fact, it is sufficient to insert the sensor 30 in recess 31 prior to assemble the first outer cover 12 to the motor cartridge 1.

The detection of the angular position of the motor shaft 8 occurs, preferably, through a series of magnets integral with the motor shaft 8, and thereby arranged at regular angular intervals according to a circumference having as its center the first longitudinal axis X. Sensor 30 is configured to detect the change in magnetic field due to the passage of the above magnets near the sensor 30 following rotation of the motor shaft 8.

Sensor 30 might be operatively connected to a control device, not shown in the drawings but in itself known. Preferably, the connection is made through cables that, still preferably, are housed in a channel made in the first inner cover 5 and/or in the first outer cover 12, whereby the channel has a first end communicating with the recess 31.

If the control device is arranged outside of the first electric motor 20, the channel is configured so as to guide the cables towards the outside of the first electric motor 20. If, on the other hand, the control device is integrated in the first electric motor 20, the channel is provided with a second end facing the control device.

Operatively, the assembly of the first electric motor kit 24 in order to obtain the first electric motor 20 shown in the Figures from 1 to 4 is accomplished through coupling the tubular sleeve 11 to the motor cartridge 1. The above mentioned coupling is made preferably through sliding the tubular sleeve 11 on the motor cartridge 1 , possibly after interposition of a lubricant layer.

Preferably, the tubular sleeve 11 exhibit a cross-section having a closed- annular shape, obtained e.g. by welding the two opposite edges of a calendared metal sheet. That, advantageously, reduces the number of operations required to obtain the coupling, limiting them to the sliding between the above mentioned two components.

In the other hand, in a variant embodiment of the invention, the tubular sleeve 11 might exhibit a cross-section having an open-annular shape. That configuration eases the insertion of the tubular sleeve 11 on the motor cartridge 1. In that case, the opposite edges of the tubular sleeve 11 might be mutually secured after coupling with the motor cartridge 1 , e.g. through welding or using per-se known connection elements.

The assembling of kit 24 might also possibly envisage securing the two first outer covers 12, 13 to the motor cartridge 1. The above mentioned securing might occur, for example, by connecting the above outer covers to the inner covers 5, 6 through the connection elements 14 previously disclosed, possibly after interposition of one or more elements of the sealing assembly 17. As an alternative to what above said, the electric motor kit 24 might be used to obtain the second electric motor 28 shown in the Figures from 6 to 8. In that case, the two second outer covers 26, 27 are secured to the motor cartridge 1 instead of the first outer covers 12, 13.

From what has been disclosed beforehand, it is understood that the electric motor kit of the invention reaches the prefixed aims.

In particular, covering a motor cartridge provided with a casing in a first material whose cost is relatively lower, with a tubular sleeve in a second material whose cost is relatively higher, allows to make an electric motor equivalent to a known-type motor whose casing is entirely made in the second material, yet having a substantially lower cost.

Moreover, the motor cartridge can be used to make an electric motor equivalent to a known-type motor whose casing casing is made in the first material, without the need to stock further high-value components.

The invention is susceptible of changes and variants, all of which are comprised in the inventive concept specified in the attached claims. In particular, the elements of the invention might be replaced by other technically equivalent elements.

Moreover, the materials might be chosen according to the needs, yet without departing from the scope of the invention.

Moreover, one or more elements of a specific embodiment of the invention that are technically equivalent to another specific embodiment of the invention might be introduced in the latter embodiment, in addition or to replace elements of the latter embodiment.

Where technical elements specified in the claims are followed by reference signs, those reference signs are included at the sole aim to enhance the intelligibility of the invention, hence they do not imply any limitation in the scope of protection claimed.