A unit for generating and treating compressed aeriform fluids, with an improved cooling system

The present invention relates to a unit for generating and treating a compressed aeriform fluid, in particular air.

More specifically, the subject of the invention is a generating and treatment unit comprising

- a positive-displacement compressor including

* a prime mover,

* a rotary shaft rotatable by the prime mover, and

* at least one cylinder in which an associated piston, coupled to the shaft by means of a crank mechanism, is mounted for sliding in a leaktight manner; and a heat exchanger for receiving and cooling the compressed fluid produced by the compressor.

The object of the present invention is to provide a generating and treatment unit of the type specified above which comprises in particular a so-called "oil-free" positive-displacement compressor, that is, a positive- displacement compressor without lubrication, which has an improved cooling system that can afford the compressor a long operative life.

This and other objects are achieved according to the invention by a unit of the type defined above, characterized in that it further comprises a tapping duct extending between the heat exchanger and that region of the at least one cylinder which is disposed between the associated piston and the shaft, the duct being suitable for supplying a flow of compressed fluid to that region in operation in a manner such that the flow of fluid can expand and be cooled further in

that region.

By virtue of this characteristic, an efficacious cooling effect is produced on the rotational bearings of the crank mechanism by means of which the or each piston is connected to the rotary shaft . This cooling is particularly important in oil-free compressors, that is, compressors without forced or splash lubrication. In fact, as is known, sliding bearings which are intended to operate without forced lubrication are provided with thin films of solid lubricant or with sealed bearing units, which are susceptible to failure at temperatures above about 70 ⁰ C. Control of their operative temperature is therefore essential for a long useful life of these bearings .

Further characteristics and advantages ^' of the invention will become clear from the following detailed description which is given purely by way of non-limiting example with reference to the appended drawings, in which:

Figure 1 is a perspective view of a unit for generating and treating air according to the present invention;

Figure 2 is another perspective view of the unit shown in Figure 1 ;

Figure 3 is a perspective view similar to that shown in Figure 1 and shows the generating and treatment unit without the cooling fans associated with its cylinders;

Figure 4 is a perspective view showing part of Figure 3 on an enlarged scale; and

Figures 5 and 6 are sections taken on lines V-V and VI-VI of Figure 3, respectively.

In Figures 1 to 3, a unit for generating and treating a compressed aeriform fluid, in particular air, according to the invention is generally indicated 1.

In the embodiment shown, the unit 1 comprises a positive- displacement compressor, generally indicated 2 in Figure 3, and an associated heat-exchanger unit, generally indicated 3 in Figures 2 et seg.

The heat-exchanger unit 3 comprises, for example, two exchange sections, each of which is of the type with parallel vanes through which a bundle of tubes arranged in parallel with one another, or a coil, extends.

In the embodiment shown, the positive-displacement compressor 2 comprises a prime mover 4 (Figures 1-3) , for example an electric motor, which rotates a crankshaft 5 in operation (Figures 3-6) . The crankshaft 5 is mounted for rotation in a substantially box-shaped rigid support casing 6 connected to the housing of the prime mover 4.

In the embodiment shown by way of example, the positive- displacement compressor 2 comprises two pairs of cylinders 7, 8 and 9, 10, arranged in opposed pairs (a "boxer" arrangement) . However, the invention is not limited to this number of cylinders or to their arrangement at 180°.

The cylinders 7-10 are connected to the support structure 6 and an associated piston is mounted for sliding in a leaktight manner in each cylinder. Only the pistons 11 and

12 which are mounted for sliding in the cylinders 9 and 10 are visible in the appended drawings (Figure 5) .

The above-mentioned pistons are coupled to the crankshaft 5 in known manner by means of respective crank mechanisms including connecting rods 13 and pins 14 for articulation between the connecting rods and the pistons (Figure 5) .

With reference to Figures 3 and 4, the cylinders 7, 9 and 8, 10, respectively, that are situated on the same side of the support structure 6 have respective intake connectors connected to corresponding intake manifolds 15 and 16. The cylinders have respective output or delivery ducts connected to corresponding portions of the heat-exchanger unit 3. The heat exchanger is intended to cool the compressed fluid which is output by the compressor 2 and is destined for a user pneumatic circuit, not shown.

The intake manifolds 15 and 16 are connected to a support plate 17 (Figures 1-3) interposed between the support structure 6 and the housing of the prime mover 4.

A fan unit, generally indicated 18 in Figures 1 and 5, is associated with the positive-displacement compressor 2. In the embodiment shown by way of example, the fan unit 18 comprises a support structure 19 which is substantially C- shaped in cross-section (Figure 5) with an upper arm or limb 20, a lower arm or limb 21 and a shaped intermediate portion 22 in which four openings 27-30 are defined, facing the cylinders 7-10, respectively. Respective electric fans 37-40 for producing an air-flow for cooling the associated cylinders of the compressor 2 are mounted in the openings (Figures 1, 5 and 6) .

The motor-driven fans 37-40 are preferably of the "suction" type with respect to the associated cylinders 7-10 although the possibility of their being of the "pusher" type is not excluded.

As can be seen in particular from Figures 1, 2 and 5, the end arms 20 and 21 of the support structure 19 are joined to the opposite ends of the two sections of the heat exchanger 3 and, together with the transverse plate 17 and with an end plate 31 (Figure 2) facing the transverse plate 17, help to define a compact, substantially parallelepipedal box-like casing enclosing the support structure 6 of the crankshaft 5 and the cylinders 7-10 of the . positive-displacement compressor.

With reference to Figures 3, 4 and 6, in the generating and treatment unit 1 according to the invention, a respective tapping duct is associated with the cylinders of the compressor which extend from the same side of the central support structure 6. In Figures 3, 4 and 6, solely the tapping duct 41 associated with the cylinders 8 and 10 is visible. With particular reference to Figure 6, the tapping duct 41 extends from the associated section of the heat exchanger 3, outside and above the support structure 6, and then extends into that structure through an opening indicated 42 (Figures 4 and 6) . In the embodiment shown, the tapping duct 41 splits inside the support structure 6 forming two branches 41a and 41b (Figures 3 and 4) which are bent into an L-shape towards the associated pistons. The terminal ends of the branches 41a and 41b of the tapping duct 41 extend in those regions of the cylinders 8 and 10 which are disposed between the associated pistons and the structure 6 in which the crankshaft 5 is supported for rotation.

As an alternative to the arrangement described above, the tapping duct 41 could extend from a point downstream of a drying device (known) connected to the output of the heat exchanger 3 or from a drain region of such a drying device .

In operation, a flow of compressed and cooled air is withdrawn from the end portion of the heat exchanger 3 through the tapping duct 41 and its terminal branches 41a and 41b and is fed into the region underlying the pistons in the cylinders 8 and 10. The flow of compressed and cooled air expands in that region and brings about effective cooling of the pistons, of the associated articulation pins 14, and of the corresponding connecting rods 13. This cooling effect prevents the temperature of the bearings of the crank mechanisms from increasing in operation so as to avoid the risk of damage to the lubricant films associated with those bearings, ensuring a corresponding extension of their useful life.

The pistons and the cylinders are also effectively cooled.

Although it is not visible in the drawings, a similar tapping duct is also provided for the cylinders 7 and 9 of the other bank.

An electronic control unit, housed, for example, in a holder

50 connected to the casing of the prime mover 4, is advantageously associated with the motor-driven fans 37-40, (Figures 1 and 3) .

The control unit is advantageously arranged to activate the motor-driven fans 37-40 with a predetermined advance with respect to the starting of the prime mover 4 and to de-

activate the motor-driven fans with a predetermined delay after the de-activation of the prime mover.

The extent of the advance in the activation of the motor- driven fans is advantageously predetermined according to the temperature detected in operation at one or more points in the unit, for example, in the vicinity of a cylinder head or in the vicinity of a crank mechanism. The same advantageously applies to the delay in the de-activation of the motor-driven fans.

The delayed switching-off of the motor-driven fans prevents or at least reduces the thermal shocks borne by the cylinders of the positive-displacement compressor.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to 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.

In embodiments not illustrated, a plurality of motor-driven fans is associated with the or each cylinder.

In other embodiments not shown a single motor-driven fan is associated with two or more cylinders.

In any case, the speed of rotation of the motor-driven fan or fans can advantageously be controlled in a manner such as to prevent the formation of ice on the heat exchanger or exchangers 3. In any case, the or each motor-driven fan and/or the

respective control can be such that the direction of rotation of the motor-driven fan or fans is reversible according to the outside temperature and/or the temperature of the aeriform fluid at the output of the heat exchanger 3. In this case, it is possible to arrange for switching of the direction of rotation according to the external climatic conditions .

This enables heated air withdrawn from the region surrounding the cylinder head or heads to be sent towards the heat exchanger, for example, in certain ambient climatic conditions. This is useful in particular when the exchanger is associated with a membrane dryer which becomes inefficient at low temperatures of the air circulating therein, in particular below 0°.

In embodiments comprising membrane ' dryers the speed of rotation of the motor-driven fan or fans can advantageously be controlled in accordance with a predetermined function of the external temperature and/or of the temperature of the aeriform fluid at the output of the heat-exchanger unit 3 to take account, for example, of the fact that the dryers generally operate inefficiently at temperatures below about 0 ⁰ C.

Finally, although the foregoing description and the appended drawings relate to a single-stage positive-displacement compressor, the invention is of course also applicable to multi-stage compressors.