Abstract:
A device ( 10 ) includes a turbine ( 22, 34 ) having an impeller ( 22 ), and an electric generator ( 12, 24 ) having a stator ( 12 ) provided with stator windings distributed around a cylindrical surface (X) coaxial to the impeller ( 22 ), and a permanent magnet ( 24 ) which is rotatable relative to the stator ( 12 ) and is drivingly connected for rotation with the impeller ( 22 ). The impeller ( 22 ) is housed inside the permanent magnet ( 24 ) and the assembly formed by the impeller ( 22 ) and by the permanent magnet ( 24 ) is housed inside the stator ( 12 ). The permanent magnet ( 24 ) is made as a single hollow cylindrical body of high magnetic density material with diametrical magnetization.

Description:
This application is a National Stage Application of PCT/IB2011/052965, filed 5 Jul. 2011, which claims benefit of Ser. No. TO2010A000578, filed 6 Jul. 2010 in Italy and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a device for generating electric power from a source of air or other gas or fluid under pressure. 
     Devices for generating low-voltage electric power (typically, at 24V) using the energy provided by a source of air under pressure are currently available on the market. Such devices basically comprise an electric generator, a radial micro-turbine coupled for rotation with the rotor of the electric generator and a nozzle through which the air under pressure provided by a source of air under pressure is directed against the blades of the micro-turbine so as to drive the micro-turbine into rotation, along with the rotor of the electric generator, thereby producing electric power from the pressure and kinetic energy of the flow of air under pressure. Such devices further comprise an electronic control unit arranged to ensure a constant output voltage independently of changes in the electric load connected to the device and in the pressure of the air under pressure supplied to the device. The arrangement of the micro-turbine in series with the electric generator makes the device rather bulky, in particular in the axial direction (i.e. in the direction of the axis of rotation of the micro-turbine and of the rotor of the electric generator). 
     An electric generator for an air tool is known from U.S.2005/0258694 and comprises a rotor provided with blades and an annular stator axially arranged between the rotor and a bearing for support of the rotor, wherein the rotor has, on its end face axially facing towards the stator, a plurality of cylindrical cavities which extend parallel to the axis of the rotor and accommodate each a respective permanent magnetic body (made for instance of neodymium-iron-boron) of cylindrical shape inserted into a respective non-magnetic body (made for instance of zinc, aluminium or brass) of cup-like shape. This known solution is however also affected by the drawback of the great axial size, since the stator is arranged axially at the side of the rotor. Moreover, this known electric generator has a high number of components. 
     A device for generating electric power from a source of air or other gas or fluid under pressure having the features set forth in the preamble of the enclosed independent claim  1  is known from U.S.2009/0224544. According to this known solution, the device comprises a plurality of permanent magnets mounted on the outer surface of a cylindrical support structure inside which the impeller of the turbine is inserted. The permanent magnets are anisotropic and have a fixed axis of magnetization, whereby they can only generate a radial magnetic field. Each pair of permanent magnets creates therefore two poles and accordingly the device will have a number of pole pairs proportional to the number of permanent magnets. Since the frequency of the electric current produced is proportional to the rotational speed and to the number of pole pairs and since a high frequency of the current may cause high hysteresis losses and high losses in the diodes of the rectifier bridge, such a known device is therefore not suitable for working at high speed. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a device for generating electric power from a source of air or other gas or fluid under pressure which is small, which has a minimum number of components and which is able to work with a high rotational speed of the impeller. 
     This and other objects are fully achieved according to the present invention by virtue of a device for generating electric power from a source of air or other gas or fluid under pressure. 
     Preferred embodiments of a device for generating electric power from a source of air or other gas or fluid under pressure according to the present invention form the subject-matter of the dependent claims, the content of which is to be intended as integral and integrating part of the present description. 
     In short, the invention is based on the idea of providing a device for generating electric power from a source of air or other gas or fluid under pressure, comprising a stator and a rotor, wherein the stator comprises in turn a winding arrangement around a cylindrical surface and wherein the rotor is mounted inside the stator coaxially thereto and comprises in turn an impeller made as an impeller of an axial turbine and a permanent magnet made as a single hollow cylindrical body of high magnetic density material with diametrical magnetization, inside which the impeller is received. Since the impeller is received inside a permanent magnet made as a hollow cylindrical body and since the assembly formed by the impeller and by the permanent magnet is in turn received in a stator having an inner cylindrical cavity, a device is provided which has at the same time a reduced axial size and a minimum number of components. Moreover, since a single permanent magnet in the shape of a hollow cylindrical body with diametrical magnetization is used, the minimum number of pole pairs (one pole pair only) is obtained and the assembly formed by the impeller and by the permanent magnet can therefore reach high rotational speeds without incurring in the above-mentioned high losses. 
     Preferably, the impeller is made as an impeller of an axial impulse turbine although other kinds of turbines might be envisaged depending of the specific applications. 
     Preferably, the device can be provided with suitably shaped discs so as to open or close air inlet channels and to allow to adjust the air flow rate, and hence the power generated by the device. 
     A device for generating electric power according to the present invention allows to provide electric power with no need of supply cables and is therefore suitable for being used for instance to supply sensors or other devices in remote areas or areas which are difficult to be reached, such as areas under risk of explosion (for instance refineries), to supply wireless receiving/transmitting nodes, to supply programmable logic controllers of portable automatic unities, or again to supply low-power pneumatic valves. A further possible field of application is for instance emergency lighting: a reservoir of air under pressure with a normally-open discharge valve, which is kept closed by a supplied solenoid, in case of black-out ensures supply of air under pressure to the generator device, which can thus supply a light source (for instance high-intensity LEDs). A device for generating electric power according to the present invention can also be used to activate a display or auxiliary lights on small pneumatic or manual tools or again to supply acoustic or optical alarms for pneumatic devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will become apparent from the following detailed description, given purely by way of non-limiting example with reference to the appended drawings, in which: 
         FIG. 1  is an axial section view of a device for generating electric power from a source of air under pressure according to a preferred embodiment of the present invention; 
         FIG. 2  is a perspective view of the impeller of the rotor of the device of  FIG. 1 ; 
         FIG. 3  is a perspective view of the distributor of the device of  FIG. 1 ; and 
         FIGS. 4 and 5  are a front elevation view and an axial section view, respectively, of the outlet disc of the device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description and claims, the terms “axial” and “radial” are used to indicate a direction parallel and a direction perpendicular to the axis of rotation of the rotor of the electric power generator device, respectively. 
     With reference to  FIG. 1 , a device for generating electric power (hereinafter referred to simply as “device”) according to a preferred embodiment of the present invention is generally indicated  10  and basically comprises:
         a stator  12  of per-se-known type, consisting of a stator winding arrangement around a hollow cylindrical surface of axis X;   a rotor  14  rotatably mounted inside the stator  12  coaxially thereto;   an inlet body  16  which is arranged upstream of the assembly formed by the stator  12  and by the rotor  14  and is provided with an inlet fitting  18  (only partially shown) for connection to a source of air or other gas or fluid under pressure (not shown); and   an outlet body  20  arranged downstream of the assembly formed by the stator  12  and by the rotor  14 .       

     The rotor  14  comprises in turn an impeller  22 , which in the illustrated embodiment is made as an impeller of an axial turbine, and a permanent magnet  24 , which is made as a single hollow cylindrical body inside which the impeller  22  is received. The impeller  22  and the permanent magnet  24  are rigidly connected to each other, advantageously by interference-fit, so as to rotate as a single body. The impeller  22  is made for instance of magnetic material, of non-magnetic metals or alloys or again of plastic material. The impeller  22  can be better observed in the perspective view of  FIG. 2 , from which in particular the shape of the blades  26  and of the channels  28  defined between them can be noticed. The impeller  22  is also provided with a shaft  30  by means of which it is rotatably mounted in the stator  12  about the axis X. The permanent magnet  24 , which forms with the stator  12  an electric generator, is advantageously made of a magnetic material with high magnetic density, such as neodymium-iron-boron, samarium-cobalt or the like. The material of the permanent magnet  24  will be chosen case by case depending also on other parameters, such as for instance the temperature of use and the mechanical strength. The permanent magnet  24  is diametrically magnetized. Preferably, the rotor  14  further comprises a sleeve  32  of composite material, in particular of carbon fibre, which encloses the permanent magnet  24  and serves to increase the mechanical strength of this latter, which in use is subject both to stresses due to the centrifugal forces and to stresses due to the difference between the thermal expansion of the material of the impeller  22  and that of the material of the permanent magnet  24 . 
     A distributor  34  is received in the inlet body  16 , at the end axially facing towards the impeller  22 , and forms with the impeller  22  an axial turbine, preferably an axial impulse turbine. The distributor  34  can be better observed in the perspective view of  FIG. 3 , from which in particular the shape of the blades  36  and of the channels  38  defined between them can be noticed. In the face of the distributor  34  axially facing towards the impeller  22  a cylindrical cavity  40  is provided, which receives a rolling bearing  42  (made for instance as a radial ball bearing) supporting the inlet-side end of the shaft  30  of the impeller  22 . Alternatively, in case of particular conditions of use, such as very high rotational speeds, long no-stop operating times etc., other types of bearings, for instance gas bearings or magnetic bearings, may be used. A pressure balancing chamber  44  is defined by the inlet body  16  between the inlet fitting  18  and the distributor  34 . 
     An outlet disc  46  is received in the outlet body  20  at the end axially facing towards the impeller  22  and has a plurality of openings  48  through which the air coming from the impeller  22  is discharged in the atmosphere. The outlet disc  46  is illustrated, both in axial section and in front elevation, in  FIGS. 4 and 5 . A cylindrical cavity  50  is provided in the face of the outlet disc  46  axially facing towards the impeller  22  and receives a rolling bearing  52  (in particular a bearing capable of withstanding both radial and axial loads, such as for instance an oblique ball bearing or one of the other types of bearings mentioned above) supporting the outlet-side end of the shaft  30  of the impeller  22 . Special suitably shaped discs (not shown) can be inserted upstream of the distributor  34  to adjust the flow rate of the intake air (or other gas or fluid). 
     In the illustrated embodiment, the inlet body  16  and the outlet body  20  are made as separate pieces which are arranged on axially opposite sides of the stator  12  and are attached to each other (for instance by screws). 
     The operation of the device  10  will be briefly illustrated here below. The air under pressure produced by the source of air under pressure at a pressure comprised for instance between 2 and 4 bar, enters the pressure balancing chamber  44  of the inlet body  16  of the device  10  through the inlet fitting  18 . In this connection, the pressure balancing chamber  44  serves to ensure a constant pressure upstream of the axial turbine. The air is then accelerated through the channels  38  of the distributor  34  until it reaches the sound speed at the inlet of the channels  28  of the impeller  22 , enters then the impeller  22  accelerating it up to a rotational speed of 100.000÷200.000 rpm, and is finally discharged in the atmosphere through the openings  48  of the outlet disc  46 . The permanent magnet  24 , which is drivingly connected for rotation with the impeller  22 , is thus also set into rotation and generates a rotary magnetic flux which induces electromotive forces in the stator windings of the stator  12 . 
     The electromotive forces so induced will be rectified by a diode bridge and suitably stabilized by means of a DC-DC converter independently of changes in the supply pressure and in the load. The converter is housed in a printed circuit board, which can preferably provide auxiliary functions, such as for instance protection against overspeed or overvoltage, analog inputs for reading sensor signals, storage of the detected data, low-consumption integrated wireless module for sending the data to a remote unit etc. The converter is suitable designed to accept in input a wide range of voltages (for instance from 0 to 30 V), as the voltage which is produced changes depending on the rotational speed of the turbine, which changes in turn depending on the input pressure and on the load. This converter also serves to supply the internal electronic components. A second DC-DC converter produces an industrial voltage of 24 V from the stabilized voltage of the first converter to supply the user load (for instance a sensor). 
     An adjusting valve, preferably a passive valve, may be provided upstream of the device to adjust the pressure of the intake air to the optimal value for the turbine yield. 
     As results from the previous description, the device according to the invention has a minimum number of components, compact sizes and a high yield. In connection with this last aspect, the integration of the impeller of the turbine and of the rotor of the electric generator in a single component allows to eliminate the losses due to the mechanical coupling of these components. 
     Moreover, as already stated above, the use of special holed discs acting as restrictor members allows to adjust the electric power produced by the device. The device can thus be designed for applications requiring high power for a short time (for instance alarms, failure signals etc.) or for applications requiring low power for a long time (for instance sensors, monitoring devices etc.). 
     Naturally, the principle of the invention remaining unchanged, the embodiments and the constructional details may vary widely from those described and illustrated purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the appended claims. 
     For instance, although the invention has been described and illustrated with reference to a turbine made as an axial impulse turbine, the turbine might be of different type depending on the specific applications.