TECHNICAL FIELD OF THE INVENTION

The present invention concerns the technical field of devices for the production of compressed gas, preferably compressed air.

In particular, the present invention concerns the technical field of volumetric compressors.

In greater detail, the present invention concerns a volumetric screw compressor with oil injection.

DESCRIPTION OF THE STATE OF THE ART

The use of devices for the generation of compressed gas is known in several sectors, typically but not exclusively in the industrial field.

Said devices for the generation of compressed gas, here below simply referred to as compressors, are suitable for the intake of a gas, typically air, and for treating the same in order to increase its pressure while it flows towards an outlet way. Among the compressors of known type, the so-called volumetric screw compressors with lubricating fluid (oil) injection offer several advantages such as, for example, high efficiency and reliability, sturdiness, limited overall dimensions etc..

Said compressors typically comprise a casing that defines a compression chamber and is provided with two suction ducts, one for the air or gas and the other for the lubricating oil or fluid, as well as with a delivery (outlet) duct for the compressed air-oil mixture. Inside the compression chamber there are two helical rotors, a male rotor (generally the driving rotor) and a female rotor (generally the driven rotor), meshing with each other.

The compression of the air-oil mixture takes place in the volume included between the teeth of the two rotors and the casing, in particular between the contact area between the two rotors and the outlet duct. In particular, during the rotation of the two rotors the contact cross section included between the outline of the male rotor and that of the female rotor is displaced, in particular it moves towards the delivery duct. In this way, the air-oil mixture included between the contact cross section and the delivery duct is compressed.

The air-oil mixture flowing out of the compression chamber is then subjected to a treatment intended to separate the oil from the compressed mixture.

The oil that has been removed from the compressed mixture is then re-introduced in the compression chamber and furthermore, through suitable channels, it can be used to lubricate the bearings or other moving members, for example the mechanical transmission members that transmit the rotary motion of the driving rotor.

The rotary motion, in fact, is transmitted to the driving rotor starting from a motive power provided by a motor through a transmission system that, in particular, can be direct (if necessary with transmission coupling) or indirect (driving belt or gearcase). In the first case the transmission ratio between the motor and the compressor is 1. In the second case the transmission ratio is multiplied or demultiplied.

Figure 1 schematically shows the operating principle of a screw compressor 1 with lubricating fluid injection according to the known art.

The compressor 1 substantially carries out a compression treatment on an incoming gas flow Fi, typically an air flow, with a compression and/or lubricating fluid, typically oil, in order to obtain a compressed gas flow Fu directed towards the outside.

The screw compressor 1 with oil injection is a machine of the rotary volumetric type. It comprises a compression chamber 2 inside which the gas and the compression fluid are compressed.

The compressor 1 comprises a suction valve 3 suited to draw the gas (typically air) and provided with an apposite suction filter 4 for conveying the air into the compression chamber 2. The compressor 1 furthermore comprises an oil supply inlet 5 for conveying the oil into the compression chamber 2.

Power means 6 (for example an electric motor or even an internal combustion engine or a similar power source) allow the activation and/or movement (in particular, the rotation) of the real compression means housed inside the compression chamber 2. The compressor 1 comprises also a separation portion (or tank) 7 arranged downstream of the compression chamber 2, in which the compressed oil/air mixture is conveyed through a delivery duct or channel (hereinafter also simply referred to as outlet) so that it can be separated and so as to obtain the outflow of compressed air 8 on one side and oil 9 on the other side. The separated oil 9 is recovered so that it can be re-introduced in the compression chamber 2 through said supply inlet 5. The reintroduction of said oil 9 in the compression chamber 2 is conditioned on its previous passage through a thermostatic valve 10, which allows the oil 9 to flow through it and towards the supply inlet 5 only if its temperature is lower than a pre-established limit temperature. In fact, inside the compression chamber 2 the oil is subjected to an increase in temperature. The thermostatic valve 10, therefore, allows the passage of oil only if its temperature is below the pre-established limit, while if the oil temperature exceeds the pre-established limit the same is conveyed into an oil cooler 1 1 that lowers its temperature before it is re-introduced in the recirculation circuit.

A filter 12 for the elimination of any impurities is preferably positioned upstream of the oil supply inlet 5.

As far as the separated compressed air 8 is concerned, it is first conveyed to an oil removal filter 13 that separates any oil residues that are present in the compressed air.

Also the residual oil recovered in this way is thus re-introduced in the compression chamber 2, in particular along a further circuit for the reintroduction of the recovered oil, along which a display 14 for monitoring oil recovery is preferably positioned.

When leaving the oil removal filter 13, the purified compressed air flows through a minimum pressure valve 15. Said valve 15 allows the air to flow through it only once the pre-established rated pressure has been reached.

The air flowing out of the minimum pressure valve 15 is preferably conveyed towards a cooler 16 where it is cooled. The cooled air is then conveyed to a usage tank 17, or as an alternative directly to the system with which it is associated. Part of the purified compressed air flowing out of the oil removal filter 13 is conveyed to the suction valve 3 through an apposite channel 58. The air conveyed through said channel 58 represents the feedback signal that signals to the suction valve 3 when the air passage needs to be closed or opened. In particular, if the air pressure in said channel 58 is lower than the pre-established rated pressure of the compressor 1 , the suction valve 3 is opened.

If, on the other hand, the air pressure in said channel 58 is higher than or equal to the pre-established rated pressure of the compressor, the suction valve 3 is closed.

Further elements, not expressly specified herein, are preferably provided for the compressor 1 , for example valves for discharging oil, if necessary, from the separation portion 7, or safety valves, or valves for discharging condensation into the air tank 17, etc.

According to an embodiment known in the art, the compression chamber is substantially tight sealed and one of its bottom sides is provided with a through hole for the through insertion of an end of the driving rotor. The end of the driving rotor protrudes externally towards the transmission unit. At the level of the through hole provided in the bottom side there are means suited to support and roll the driving rotor, typically constituted by roller bearings.

The transmission unit is in turn arranged inside a housing casing that defines an independent chamber with respect to the body of the compressor. For this purpose, the casing comprises two substantially flat walls opposite each other, the first one of which is positioned in front of the motor, while the other wall is positioned in front of and fixed to the bottom side of the compression chamber from which the end of the driving rotor projects. The two substantially flat walls of the casing are connected to each other through a substantially truncated-cone shaped wall that therefore defines, together with the walls, a sealed (tight) inner space housing the transmission mechanisms between the motor and the end of the driving rotor (couplings, gears etc.).

The end of the driving rotor that projects from the compression chamber fits into the casing of the transmission unit, in a special through hole made in the wall of the casing, so that it meshes with the inner transmission mechanisms.

Inside the casing there is a given quantity of lubricating oil for the inner transmission mechanisms, preferably an oil different from that used for the compression chamber (oils with different viscosity and composition).

The solution known in the art, however, poses some recognized drawbacks.

A first drawback is related to the constructive complexity that characterizes this type of compressors, which leads to an increase in their weight and overall dimensions.

Said constructive complexity also increases the tendency of the various parts making up the compressor to wear out.

A further drawback deriving from said constructive complexity is the risk of errors being made during the assembly operations, which may lead to wear and noise exceeding the acceptable levels.

Another drawback lies in the need to use particularly sensitive and expensive sealing elements in order to ensure that the tightness obtained is sufficient to resist the pressure difference of the oils contained in the compression chamber and in the casing of the transmission unit and thus to prevent the two oils from flowing therethrough and mixing. It is thus the main object of the present invention to eliminate or at least partially resolve the problems mentioned above that characterize the volumetric compressors carried out according to the known art.

In particular, it is one object of the present invention to provide a transmission device for volumetric compressors that is characterized by a simple structure, with minimal overall dimensions and reduced weight.

It is another object of the present invention to provide a volumetric screw compressor that is more reliable and more efficient compared to the compressors known in the art.

It is another object of the present invention to provide a volumetric screw compressor with production and/or maintenance times and/or costs lower than those of the compressors known in the art.

It is a further object of the present invention to provide a volumetric compressor that is less noisy than the compressors known in the art.

SUMMARY OF THE PRESENT INVENTION

The present invention is based on the general consideration according to which the problems found in the art can be at least partially overcome by means of a gas compression device, or compressor, using a compression fluid, wherein said compressor comprises a compression chamber for said gas housing at least one driving compression rotor, a power source comprising a transmission shaft and a transmission unit interposed between the power source and the driving rotor in such a way as to transmit the rotation of the transmission shaft to the driving rotor, containment means defining a housing chamber suited to accommodate said transmission unit, and wherein a wall of the compression chamber is at least partially defined by a wall of the containment means of the transmission unit.

According to a first aspect of the present invention, therefore, the subject of the same is a compression device suited to compress a gas by means of a compression fluid, said compression device comprising:

- a compression chamber for the generation of a compressed mixture of said gas and said compression fluid;

- a first driving compression rotor and a second compression rotor mutually meshing with each other and rotatingly housed inside said compression chamber, said first driving rotor comprising an end that serves for moving it and projects from a wall of said compression chamber;

- a power source comprising a transmission shaft suited to be set rotating by said power source;

- a transmission unit interposed between said power source and said first driving rotor in such a way as to transmit the rotation of said transmission shaft to said first driving rotor;

- containment means that define a housing chamber suited to house said transmission unit, wherein said wall of said compression chamber is at least partially defined by a wall belonging to said containment means of said transmission unit.

In a preferred embodiment, the transmission unit comprises one or more transmission gears.

Preferably, the housing chamber that accommodates the transmission gears is tight sealed.

The transmission gears preferably comprise a first gear fixed to an end of the transmission shaft and a second gear fixed to an end of the driving rotor, the first and the second gear mutually meshing with each other.

Advantageously, the first and the second gear define a transmission ratio different from 1 between the transmission shaft and the driving rotor.

In another preferred embodiment of the invention, the transmission unit comprises a coupling.

According to a preferred embodiment of the invention, the end of the first driving rotor is partially housed in a through hole made in said wall.

The device according to the invention preferably comprises sealing means interposed between the through hole and the end of the driving rotor in such a way as to guarantee the fluid-dynamic separation between the compression chamber and the housing chamber of the transmission unit.

In a preferred embodiment, the sealing means comprise a sealing element having at least one elastic portion suited to be placed in contact with the outside of the end of the driving rotor.

Furthermore, an annular element is preferably interposed between the sealing element and the end of the driving rotor.

Advantageously, said annular element serves as an interface element between the sealing element and the end of the driving rotor and is suited to prevent the wear of the end of the driving rotor.

According to a preferred embodiment of the invention, the device comprises supporting and rolling means interposed between the through hole and the end of the driving rotor, said supporting and rolling means being housed in said wall. Preferably, the supporting and rolling means comprise a roller bearing.

In a preferred embodiment, the containment means are provided with an opening suited to house and be coupled with a portion of the power source from which the transmission shaft projects.

Advantageously, the housing chamber of the transmission unit is suited to receive lubricating oil for the transmission unit.

The housing chamber preferably comprises an opening with a corresponding closing plug, wherein said opening allows the lubricating oil to be filled in and/or topped up.

Preferably, the housing chamber furthermore comprises a tap for discharging the lubricating oil from the housing chamber.

In a preferred embodiment, the containment means are obtained by assembling a plurality of component parts.

In another preferred embodiment of the invention, the containment means are made in a single piece through a casting process.

Preferably, the lubricating oil level inside the housing chamber is such that at least one of the gears is at least partially immersed in the lubricating oil.

Preferably, the power source is constituted by an electric motor.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, objectives and characteristics as well as further embodiments of the present invention are defined in the claims and are clarified below through the following description with reference to the attached drawings. It should however be noticed that the present invention is not limited to the embodiment described here below and illustrated in the drawings; on the contrary, all those variants and/or changes to the embodiment described below and shown in the attached drawings that are clear and apparent to the expert in the art fall within the scope of the present invention.

In particular, in the figures:

- Figure 1 shows a schematic view of the operating principle of a compressor according to the known art;

- Figure 2 shows an axonometric view of a compressor according to a preferred embodiment of the invention;

- Figure 3 shows a side view of the compressor of Figure 2;

- Figure 4 shows a sectional view according to plane IV-IV of Figure 3 ; - Figure 5 shows a sectional view according to plane V-V of Figure 3;

- Figure 6 shows a sectional view according to plane VI- VI of Figure 3;

- Figure 7 shows an enlarged detail of Figure 4.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Even though the present invention is described here below with reference to its embodiment illustrated in the drawings, the present invention is not limited to the embodiment described below and illustrated in the drawings. On the contrary, the embodiment described here below and represented in the drawings clarifies some aspects of the present invention, the scope of which is in any case defined in the claims.

The present invention can be especially applied in the field of production of volumetric compressors for various sectors, for example in the mining, building construction or industrial sector. In particular, the present invention can be successfully but not exclusively applied in the production of a volumetric screw compressor with lubricating fluid (oil) injection powered by an electric motor. It should however be noted that the present invention is not limited to this type of application. On the contrary, the present invention can be conveniently applied in all those cases requiring the use of a volumetric screw compressor, for example an engine-driven compressor (internal combustion engine).

With reference to the figures, it is possible to observe the configuration and mutual position of the main component parts of the compressor 1. whose numbering reflects the description provided above with reference to the compressor illustrated in the diagram of Figure 1. In particular, it is possible to identify the air filter 4, the compression chamber 2, the power means (motor) 6 with the transmission shaft (or pinion) 6a, the compression means 6mc, 6fc, the oil removal filter 13 and the separation tank 7.

The compression chamber 2 is defined inside the main body 30 of the compressor I preferably obtained through a shell casting process, preferably through a metallic material casting process.

Preferably, the metallic material comprises aluminium.

In variant embodiments, the main body can be advantageously obtained by sand molding a cast iron alloy.

Inside the compression chamber 2 (see Figure 4) there are the compression means 6mc and 6fc. respectively male (or driving) and female (or driven), of the air/ fluid mixture. The methods for compressing the mixture are known per se, therefore a detailed description of the same is omitted.

It should also be briefly underlined that the compression means comprise, in fact, two helical rotors 6mc and 6fc, a male rotor (usually a driving rotor) and a female rotor (usually a driven rotor) meshing with each other. The compression of the gas/oil mixture takes place in the volume included between the tooths of the two rotors 6mc and 6fc and the body that defines the compression chamber 2; during rotation the contact part included between the profile of the male rotor and that of the female rotor is displaced from a suction side to a delivery side (from right to left in Figure 4), so that the quantity of air included therein is compressed due to the reduction of the available volume.

Said first and said second rotor 6mc and 6fc are arranged longitudinally, parallel to a main axis X, and therefore substantially parallel to each other and rotate along corresponding rotation axes that are also substantially parallel to the main axis X of the compression chamber 2.

The power means 6 preferably comprise an electric motor suited to rotate a transmission shaft 6a to which a first gear 6m is rigidly fixed.

In variant embodiments of the invention, the power means may be of a different type, for example an internal combustion engine.

A second gear 6c, integral with the driving rotor 6mc of the compressor, meshes with the first gear 6m so that the rotation of the transmission shaft 6a produced by the motor 6 sets rotating (in two opposite rotation directions) the first and the second gear 6m and 6c and therefore the driving rotor 6mc that in turn sets the driven rotor 6fc rotating.

In this way, the rotation of the transmission shaft 6a is transmitted to the male driving rotor 6mc (that in turn sets the female driven rotor 6fc rotating) according to a transmission ratio that is equal to the transmission ratio of the gears (or pinions) 6m and 6c.

Obviously, the number of transmission gears can vary according to the needs and/or circumstances; for example, one or more additional gears (or pinions) can be interposed between the pinion 6m and the pinion 6c, according to the desired transmission ratio. In the same way, also the type of gears or pinions can vary according to the needs and/or circumstances; for example, conical or similar pinions can be provided.

In another embodiment, the transmission ratio may be set as equal to 1 and the transmission gears will preferably constitute an intermediate coupling between the transmission shaft 6a of the motor 6 and the male driving rotor 6mc, for example a flexible coupling or a cardan joint or a similar element. The intermediate coupling, furthermore, is preferably made in such a way as to overcome any misalignment between the transmission shaft 6a of the motor 6 and the male driving rotor 6mc, for example using an Oldham coupling.

On the upper part of the main body 30 there is the air suction valve 3 with the respective filter 4.

The air suction valve 3 communicates with the compression chamber 2 through an apposite air suction channel (not represented in the figures). Said air suction channel is preferably created in the main body 30.

As regards the oil supply to the compression chamber 2, this is obtained by means of a recirculation circuit (not illustrated in the figures) that draws the oil from the bottom of the tank 7 and then re-introduces it into the compression chamber 2.

The oil is drawn from the bottom of the tank 7 through a drawing pipe (not illustrated in the drawings), due to the effect of the pressure present inside the tank 7 itself, and from there it is conveyed to the compression chamber 2 possibly through a thermostatic valve that, if the oil temperature is correct, meaning below a minimum allowed value, directs the oil flow towards an oil filter and from there to the compression chamber 2. Vice versa, if the oil temperature exceeds the limit temperature, the thermostatic valve directs the oil flow towards a cooler, not illustrated herein, by means of a duct connected to an apposite outlet.

The oil cooled by the cooler flows back into the circuit upstream of the thermostatic valve through a duct connected to an apposite inlet.

The gears or pinions, generally referred to as "transmission" or "transmission unit" here below, and through which the rotation of the transmission shaft 6a of the motor 6 is transmitted to the compression rotors, in particular to the male driving rotor 6mc, are located inside containment means 50.

The containment means 50 contribute to defining a housing chamber 50i for the transmission. Said housing chamber 50i of the transmission is advantageously an independent chamber and therefore from a fluid-dynamic point of view it is separated from the rest of the compressor 1, in particular from the compression chamber 2. For this purpose, the containment means 50 comprise two substantially flat walls opposing each other, the first wall 50b of which is placed in front of the compression chamber 2 (between the compression chamber 2 and the motor 6), while the other (second) wall 50c is placed in front of the motor 6. The second wall 50c is provided with an opening 51 that is coupled with the front portion 160 of the motor 6 from which the transmission shaft 6a projects.

The two walls 50b and 50c of the containment means 50 are substantially flat and connected to each other through an oblique wall 50d, substantially in the shape of a truncated cone. The two walls 50b and 50c, the oblique wall 50d and the front portion 160 of the motor 6 define said (tight) sealed housing chamber 50i that accommodates the transmission gears 6m and 6c.

According to an innovative aspect of the present invention, the first wall 50b of the containment means 50 of the transmission that is positioned in front of the compression chamber 2 constitutes, at least partially, also the wall that delimits/closes the compression chamber 2 in the direction of the housing chamber 50i of the transmission.

In other words, the wall that delimits the compression chamber 2 in the direction of the housing chamber 50i of the transmission is defined, at least partially, by a first wall 50b that belongs to the containment means 50 of the transmission itself. The containment means 50 are associated with the main body 30, in which the compression chamber 2 is defined, through fixing means 40. Said fixing means 40 preferably comprise fixing screws 41 (in the embodiment illustrated herein there are four screws 41 , as shown in Figure 6).

The containment means 50 are coupled with the motor 9 through fixing means 94 preferably comprising fixing screws 95 (in the embodiment illustrated herein there are four screws 95, as shown in Figure 5).

As can be seen in the detail shown in Figure 7, the first wall 50b of the containment means 50 of the transmission is preferably provided with a through hole 60 through which the projecting end 66 of the driving rotor 6mc is introduced. Advantageously, at the level of the through hole 60 there are the supporting and rolling means 70 of the driving rotor 6mc. The supporting and rolling means 70 preferably comprise a rolling bearing 71 , more preferably a roller bearing.

Obviously, other supporting and rolling means of an equivalent type can be used. Sealing means 80 are arranged at the level of said through hole 60 for the purpose of guaranteeing the tightness of the compression chamber 2 and of the housing chamber 50i of the transmission as well as, preferably, the fluid-dynamic separation between the two chambers.

Preferably, the sealing means 80 comprise a sealing element 81 arranged coaxially and externally to the projecting end 66 of the driving rotor 6mc.

In the embodiment described herein, the sealing element 81 comprises an external annular portion 82 from which two diverging elastic tabs 82a, 82b project radially towards the inside and come to bear against an annular element 83 that is fitted on the outside of the end 66 of the driving rotor 6mc. A spacer 82c preferably maintains the two tabs 82a, 82b in their diverging position. Said annular element 83 guarantees a correct interface between the sealing element 81 and the end 66 of the driving rotor 6mc and is suited to prevent the wear of said end and the consequently reduced tightness.

Preferably, the annular element 83 is made of case-hardened and rectified steel. In a variant embodiment, however, the annular element 83 may be absent and the two elastic tabs 82a, 82b may be arranged so that they directly bear against the external surface of the end 66 of the driving rotor 6mc.

In further construction variants, furthermore, a different number of elastic tabs may be provided, or even one elastic tab only.

Furthermore, the shape of said elastic tabs may be different from the diverging shape illustrated above.

In the embodiment illustrated herein, the sealing element 81 is accommodated inside an annular seat 90 created in a flange 91 that is removably associated with the first wall 50b of the containment means 50. The flange 91 is removably associated with the first wall 50b through fixing screws 92a, 92b, 92c (the three of them are visible only in Figure 6).

In variant embodiments, the sealing element 81 may be kept in its position by means of different solutions. For example, the housing seat may be made directly in the first wall 50b and in this case a further element as the flange 91 would be useless.

A predefined quantity of lubricating oil O is gathered on the bottom of the housing chamber 50i of the transmission; in particular, said predefined quantity of lubricating oil O is such that at least one of the gears 6m and 6c is at least partially immersed in said lubricating oil.

This solution guarantees the lubrication of the gears 6m and 6c; in particular, the gear 6m is lubricated directly (as it is at least partially immersed in the oil), while the gear 6c is at least lubricated indirectly (in the case where it is not at least partially immersed in the oil O), thanks to the oil gathered by the gear 6m during its rotation.

The housing chamber 50i of the transmission furthermore comprises a top-up opening with a corresponding plug 52, and a discharge tap 51, visible in Figure 6. The plug 52 thus makes it possible to top up the oil as desired inside the chamber, while the tap 51 makes it possible to empty the chamber or in any case to remove the oil from the same, for example when the oil has lost the viscosity that is necessary to guarantee the correct lubrication of the gears 6m and 6c.

Advantageusly, the containment means 50 are made in a single piece, preferably through a casting process. Obviously, different configurations of the containment means 50 are possible. For example, the same can be made by assembling different parts (fixing them together with screws or welding them, etc.). Also for the selection of the materials to be used to make the containment means there are several alternatives; aluminium offers the best advantages in terms of resistance and reduced weight.

The compressor according to the present embodiment of the invention allows different oils to be used respectively for compressing the gas and for lubricating the transmission gears, in fact it is possible to select oils with different viscosity and composition suitable for use in the two chambers.

The embodiment of the present invention just described above makes it possible to overcome or at least partially reduce the drawbacks posed by the compressors known in the art.

Furthermore, the delimitation of the compression chamber 2 in the direction of the housing chamber 50i of the transmission by means of a wall belonging to the containment means 50 of the transmission makes it possible to simplify the construction of the compressor, reducing its size and thus its overall dimensions and its overall weight. In particular, the compressor according to the invention has a reduced length, as a wall present in the known compressors between the compression chamber and the housing chamber of the transmission has been eliminated.

The steps necessary to assemble the compressor that is the subject of the invention are simplified and the risk of errors during assembly is reduced.

This leads to a reduction in production and/or maintenance times and/or costs compared to the compressors known in the art. In fact, the reduced size and the overall weight of the compressor positively affect its reliability and efficiency, in particular as regards the vibrations to which the compressor is subjected during operation.

The components of the volumetric compressor according to the present invention are less subject to wear and therefore the compressor is more reliable and less noisy than the compressors of known type.

Furthermore, the lubrication of the gears is simple, reliable and needs minimal maintenance.

The description provided above, therefore, shows that the compressor according to the present invention makes it possible to achieve the set objects and, in particular, can be produced in a simplified manner at reduced costs and is characterized by reduced weight and overall dimensions.

While the present invention has been described with reference to the embodiment illustrated in the drawings, it should be noted that the present invention is not limited to the particular embodiment illustrated in the drawings and described herein; on the contrary, further variants of the embodiment described above fall within the scope of the invention, which is defined by the following claims.