Field of the Invention The present invention refers to a compressor for refrigerant gas recovering machines of refrigeration systems, more particularly to rotary hermetic compressors of such recovering machines. Background of the Invention One utilization of the rotary compressors is in gas recovering machines of refrigeration systems, in which said compressors pump the gas from these systems to tanks or reservoirs, preventing the gas from escaping to the atmosphere, where this type of gas, mainly those consisting of chlorine, such as CFC and HCFC, interact whith the ozone layer, destroying it. This gas transfer to an adequate reservoir is used when the refrigeration system requires maintenance or replacement of the compressor of said system. A gas recovering machine of refrigeration systems comprises a rotary compressor, communicating with an inlet valve and a recovering cylinder, said inlet valve being disposed at the suction line of the refrigeration system, whose refrigerant gas is to be pumped to said recovering cylinder. After the valve has been connected to the suction line of the refrigeration system, the rotary compressor is turned on and the gas pumping is started, from the inside of the system to the inside of the cylinder, said pumping continuing until a determined level of decompression is reached in the refrigeration system, indicating the end of the pumping operation and making the compressor stop. Due to the pumping, there is a pressure increase in the recovering cylinder. To avoid that the gas, which is now stored inside the cylinder, returns to the compressor and consequently to the atmosphere, due to the pressure differential caused by the compressor, a service valve

is closed, interrupting the communication between the cylinder and the rest of the gas recovering machine. Nevertheless, the residual gas inside the compressor (up to 40% of the total of gas of the refrigeration system) remains in said compressor under high pressure, which is equal to that inside the recovering cylinder. After the refrigerant gas has been removed from the refrigeration system, the latter is submitted to a "washing operation" with nitrogen, which is removed together with the residues of the refrigerant gas from said system, by a process similar to the removal of refrigerant gas. In this case, when the compressor is disconnected from the recovering cylinder, the nitrogen-refrigerant gas residue mixture is expelled directly to the atmosphere.

The rotary compressors used in these recovering machines comprise a housing, inside which there is mounted an electric motor that drives the pumping mechanism of the compressor. This mechanism is connected to the housing through suction and discharge systems, the suction system being a hermetic system and consisting of a tube directly connecting the outside of the housing with the pumping mechanism, thereby avoiding the contact between the gas being pumped and the inside of the housing.

The discharge system consists of a discharge valve, which discharges the gas to the inside of a discharge chamber and, thus, to the inside of the housing, which is under high pressure. Inside the chamber, the gas is conducted to a discharge tube.

This construction has the inconvenience of permitting the contact between the pumping gas, which is normally contaminated, and the internal parts of the housing, motor and lubricating oil. This contact permits the occurrence of chemical reactions that are prejudicial to both the oil and motor, impairing the operation of

the compressor.

Another inconvenience of this construction is the presence of remaining gas inside the housing at the end of the gas removing operation from the refrigeration system.

This gas reaches the atmosphere, resulting in the damages cited above.

Disclosure of the Invention

Thus, it is the object of the present invention to provide a compressor for refrigerant gas recovering machines, which maximizes the amount of refrigerant gas pumped from a refrigeration system to an appropriate reservoir, but which minimizes the amount of said gas to the inside of the compressor housing and to the atmosphere.

This and other objectives are achieved by a compressor for a refrigerant gas recovering machine, of the type comprising a housing, which has opposite end walls and a surrounding lateral wall, whereto is attached a cylinder, lodging a piston driven by an eccentric shaft that is supported by at least one main bearing, said cylinder being provided with an end cover, carrying a discharge chamber having a gas outlet orifice and an opening, communicating with the cylinder inside through a discharge valve, the discharge chamber being a hermetic chamber having the gas outlet orifice connected and opened to an internal end of a discharge tube, which has an external end projecting outwardly from the housing. Brief Description of the Drawings

The invention will be described below, with reference to the attached drawings, in which:

Fig. 1 shows schematically a longitudinal sectional view of a horizontal shaft rotary compressor of a recovering machine, according to the prior art;

Fig. 2 shows schematically a longitudinal sectional

view of a vertical shaft rotary compressor of a recovering machine, according to the prior art; Fig. 3 shows schematically a longitudinal sectional view of a horizontal shaft rotary compressor of a recovering machine, according to the present invention; Fig. 4 shows schematically a longitudinal sectional view of part of the sub bearing of a horizontal shaft rotary compressor, where the suction and discharge chambers are defined, according to the present invention; and

Fig. 5 shows schematically a longitudinal sectional view of a vertical shaft rotary compressor of a recovering machine, according to the present invention. Best Mode of Carrying Out the Invention According to figures 1 and 2, there are provided rolling piston rotary compressors, of the type used in refrigerant gas recovering machines of refrigeration systems, comprising a housing 1, whereto is rigidly attached a cylinder 2, lodging a rolling piston 3 driven by an eccentric shaft 4, which is supported by a main bearing 5 and a sub bearing 6 and which rotates jointly with the rotor of an electric motor M, mounted to said eccentric shaft 4. The housing 1 has a pair of opposite end walls and a surrounding lateral wall, at the bottom of said housing a sump being provided for the oil that lubricates the compressor components. In this construction, the sub bearing 6 also acts as an end cover for the cylinder 2. The movement of the eccentric shaft 4 inside said cylinder 2 defines in the latter a suction chamber 7 and a compression chamber, not illustrated, which selectively communicates, by the actuation of a discharge valve 8, with a discharge chamber 9 to be described ahead. In the horizontal shaft compressors, the discharge valve 8 is lodged in a gas discharge orifice 6a, in the form of an axial passage, provided at a flange portion 6b of the sub

bearing 6, while in the vertical shaft compressors, said axial passage is provided at a flange portion of the main bearing, not illustrated. The discharge chamber 9 is defined as a cavity provided at a cylindrical end cover 10, preferably annular, having a central tubular portion 11 mounted to a free end portion of the eccentric shaft 4 and having an end face opened to the adjacent face of the flange portion 6b of the sub bearing 6, to which said end cover 10 is mounted. Though there has been illustrated the end cover 10 mounted to the sub bearing 6, said assembly may eventually be effected at the main bearing 5, provided that the constructive form of said end cover 10 allows the execution of said assembly , which is a difficult task, due to the space available in this region inside the housing 1.

The suction chamber 7 communicates with the outside of the housing 1 through a suction tube 7a, having an internal end opened to a bore 2a provided along the inside of the cylinder 2 and communicating with said suction chamber 7.

According to the prior art, the gas drawn from the refrigeration system is released to the discharge chamber 9 and therefrom to the inside of the housing 1, upon the opening of the discharge valve 8, which occurs when the pressure inside the compression chamber equals the high pressure inside the housing 1. Up to this instant, said discharge valve 8 remains closed, preventing the high pressure gas from returning to the inside of the housing, to the suction side of the compressor and refrigeration system, thereby avoiding that a pressure balance is reached between the parts. Nevertheless, when the pressure at the compression side is even with the pressure inside the housing 1, the discharge valve 8 is opened and the refrigerant gas pumped from the refrigeration system is liberated to

the discharge chamber 9 and therefrom to the inside of the housing 1 and to a discharge tube 9a, which has an internal end opened to the inside of said housing 1 and an opposite end projecting outwardly from the external surface of said housing 1. The housing 1 further has a process tube la, which is normally used for service and/or replacement of oil of the compressor after a certain working period. According to the present invention, the gas removed from the refrigeration system is directly and hermetically led to an adequate refrigerant gas reservoir, such as a recovering cylinder (not illustrated) , without any contact with the inside of the housing 1. In this solution, the process tube la is normally closed.

In the preferred illustrated constructive form, the end cover 10 carries a discharge chamber 20, which is annular and hermetic and which communicates with the refrigerant gas recovering cylinder, through a discharge tube 30, having an internal end 31 opened to a gas outlet orifice 21 provided at an end wall 12 of the end cover 10, preferably opposed to an end wall 13 thereof where there is defined an opening 22 of said discharge chamber 20, facing the adjacent face of the flange portion 6b of the sub bearing 6, whereto said end cover 10 is mounted. In the preferred illustrated form, the opening 22 occupies the whole end wall 13. The discharge tube 30 further has an external end 32, projecting outwardly from the external surface of the housing 1 and connected to the recovering cylinder by adequate means.

When the compressor is of the horizontal shaft type, the external end 32 of the discharge tube 30 reaches the external medium of the housing 1 preferably by the end wall of the latter that is adjacent to the sub bearing, where the discharge chamber is defined. In the

case of a vertical shaft compressor, said external end 32 of the discharge tube 30 is projected outwardly from the housing 1 through a portion of the lateral wall surrounding said housing 1. In this case, the discharge tube 30 has a portion of its extension that is curved and immersed in the oil of the sump of said housing 1. The curvature is defined in function of the portion of the surrounding lateral wall to be reached by the external end 32 of the discharge tube 30. In order to prevent the gas from escaping through the edges of said end wall 13 that are disposed adjacent to the sub bearing 6, the end cover 10 is mounted against said sub bearing 6, pressing a sealing element 40 in the form of a sealing ring, such as illustrated in figure 4.

Though not illustrated, the discharge chamber 20 of the present invention may be defined as a cavity in the end cover or in the body of the main bearing or sub bearing, said cavity communicating with the discharge chamber of the cylinder and discharge tube, through orifices provided on said end cover or bearing. The discharge chamber constructed in this manner avoids that the residual gas inside the compressor escapes to the inside of the housing thereof or to the atmosphere. When the suction pressure reaches the level which determines the end of gas removing operation from the inside of a refrigeration system, the discharge valve 8 prevents the low pressure gas from reaching the discharge chamber and consequently the outside of the housing. Though not described or illustrated, the present invention is also applied to reciprocating type compressors of recovering machines.