DESCRIPTION

TECHNICAL FIELD OF THE INVENTION

CNG mechanical compressors for compressing methane gas to be used in the automotive sector.

STATE OF THE ART

In CNG mechanical compressors for compressing methane gas to be used in the automotive sector, during operation a large quantity of lubricating oil flows from the crank mechanism area to the methane gas sector through the rod that transmits motion from the crosshead to the gas piston, with a consequent drastic decrease in the level of lubricant oil, which is essential for the lubrication of the entire crank mechanism, in the block. Owing to said high consumption of oil, it is necessary to top up the lubricant oil with an average quantity of approximately 4 kg every 24 hours of operation (about 166 grams/hour).

The mechanical compressors that are the subject of the present invention are provided with aluminium crossheads that slide directly in contact with the steel guide jacket and, in order to prevent any seizure, lubricant oil is sprayed from the guide jackets directly onto the contact surface of the crossheads through two nozzles with 3 mm diameter with an adjustable pressure of approximately 2 bars. This type of forced lubrication is practically compulsory if one wants to prevent any seizure of the system. A huge quantity of oil like this, furthermore, is very difficult to be disposed of without having oil sticking to the rod due to the rattling effect, in fact the rod then brings the oil along to the gas phase, where the oil in turn is collected by the gas being compressed and conveyed to the compressed gas accumulation tank, and will never return to the block.

MAIN CHARACTERISTICS OF THE INVENTION

The invention makes it possible to top up lubricating oil with quantities ranging between 6 and 30 grams/hour. The technical invention, the technical drawings of which are attached hereto, consists in the creation of a system that allows the crosshead to operate on the guide jacket without resting directly on the latter, as is presently the case in many mechanical compressors, but resting on special sliding blocks made of a plastic material with high resistance to friction that therefore need a very small quantity of lubricant while at the same time guaranteeing that there will be no seizure problems. This embodiment of the crosshead is complemented by a stuffing box unit provided with special packings made of a suitable plastic material that make it possible to hold and discharge into the block large quantities of lubricant without overheating the rod, even on the first start. It is very important to avoid overheating the rod, as if this occurred it could in turn "bake" the packings and thus negatively affect their efficiency. The discharge of the lubricant deposited on the rod by the packings of the stuffing box unit is guaranteed by special holes and channels, designed for this purpose, which are located in the stuffing box unit and in the supporting flange.

The rod will be made with such materials, heat treatments and geometrical shape as to allow - once it has been tightened to the crosshead with a lock nut - a linear transmission of motion, guaranteeing that the stuffing box unit holds a larger quantity of lubricating oil. Using special shutter elements mounted on the lubrication holes in the steel guide jackets, it is possible to reduce the flow rate of lubricating oil on the crosshead. Finally, the rod is separated from the crosshead by means of a special partition, in such a way as to prevent the lubricating oil from being deposited on the rod as a consequence of rattling.

The drawings of the details are attached hereto.

DESCRIPTION OF THE DRA WINGS

Figures 1.1 and 1.2 respectively show an axonometric view and a sectional view of the new crosshead (1).

The new crosshead (1) is generically parallelepiped in shape, with genetically rectangular cross section. The two short sides (1.1) of said cross section of said crosshead (1) are arched and are provided with recesses or seats (1.1a) suited to house anti-friction elements or sliding blocks, not illustrated in the figure, suited to facilitate the sliding movement of said crosshead (1) in the corresponding guide jacket in the block.

Inside said crosshead (1) there is a compartment (1.2) that is suited to house the big end of the connecting rod allowing the movement of the crosshead (1) itself, while the long sides (1.3) of the generically rectangular cross section are provided with holes (1.3a) suited to house the pin of the connecting rod.

In the side of the crosshead (1) opposite the side where the connecting rod is inserted there is a threaded hole (1.4) that houses an element (2) ensuring connection with the rod.

Figures 2.1 and 2.2 respectively show a front view and a sectional view of the new connection element (2) suited to ensure connection with the piston rod.

The new connection element (2) is tubular in shape and has a flat ring (2.1) at the level of one of its two ends, said ring (2.1) being orthogonal to the axis of the cylindrical portion.

Said new connection element (2) is provided with a threaded centre hole (2.2) for connection to the rod (3), while its outer surface (2.3) is threaded in order to allow it to be introduced in and connected to the threaded hole (1.4) of the crosshead (1). Figure 3 shows a side view of the connection rod (3) ensuring connection between the piston and the crosshead (1) through the relative connection element (2).

Figure 4.1 shows a sectional view of the stuffing element (4), while Figures 4.2 and 4.3 show two axonometric views of the same stuffing element (4).

Said stuffing element (4) has a generically cylindrical shape with a coaxial centre hole (4.1) for the passage of the rod (3).

Inside said coaxial centre hole (4.1) there is a first series of annular grooves and/or recesses (4.2) suited to house sealing elements and/or packings.

Suitable holes and ducts (4.3) present in the body of the stuffing element (4) place the spaces between said first annular grooves or recesses (4.2) of the sealing elements and/or packings in communication with the circular surface (4.4) of the body of the stuffing element (4) facing towards the crosshead (1) and towards the block.

On the same circular surface (4.4) of the body of the stuffing element (4) facing towards the crosshead there are holes (4.5) suited to ensure connection and union with the flange (5) that supports the stuffing element (4).

Inside said coaxial centre hole (4.1) and in proximity to its end opposite the crosshead (1), the stuffing element (4) is provided with a second series of annular grooves and/or recesses (4.6) suited to house sealing elements and/or packings intended to prevent any blow-by of gas towards the sliding jacket of the crosshead (1).

There is a further duct (4.7) suited to connect the space of the centre hole (4.1) of the stuffing element (1) included between the sealing elements and/or packings provided for the lubricant and the sealing elements and/or packings provided for the gas with the outside of the stuffing element (1) and with external ducts and sensors, in such a way as to detect any gas leakages through the stuffing element (1) due to the wear of the gas sealing elements and/or packings.

Figures 5.1, 5.2, 5.3 respectively show a front view, a sectional view and an axonometric view of the flange (5) that supports the stuffing element (4), said flange (5) being constituted by a disc-shaped element provided with a centre hole (5.1) for the passage of the rod (3), having holes (5.2) for the screws providing connection with the stuffing element (4) and having channels (5.4) suited to convey the lubricant flowing through the holes (4.3) in the stuffing element (4) towards the block.

Figure 6 shows a shutter element (6) with hexagonal head (6.1), threaded body (6.2) and a cylindrical projection (6.3). Two or more shutter elements (6) are suited to decrease and/or adjust the flow rate of lubricant on the crosshead (1). Said shutter elements (6) are mounted on the ends of each guide jacket in which the crosshead slides (1).

Figures 7.1 and 7.2 respectively show a side view and a front view of the withdrawable partition (7) comprising two semi-circular elements (7a, 7b) suited to be connected to each other so that they are fixed to the rod (3) in proximity to the crosshead (1).

Figure 8 shows a sectional view illustrating the various parts mentioned above when joined and connected to one another.

These are the schematic outlines that are sufficient to any person skilled in the art to carry out the invention; consequently, on practical application variants may be developed that do not affect the substance of the innovative concept expressed herein.

Therefore, with reference to the above description and the attached drawings, the following claims are expressed.