Gas and oil cooling system for a hermetic compressor

Patent of Invention for "GAS AND OIL COOLING SYSTEM IN A HERMETIC COMPRESSOR" for small refrigeration machines of the type including an assembly wherein is defined a cylinder housing a piston driven from a crankshaft coupled to an electric motor and forming suction and compression chambers inside the cylinder, these elements being assembled inside a sealed shell acting as a lubricant oil sump and incorporating independent lubricant oil outlet and return tubes connected to a heat exchanger external to the shell. The system in question includes oil pumping means (20) assembled on the shaft (5) having its suction (24a) connected to the lubricant oil contained in the bottom of shell (1) and its discharge (24b) connected to the oil outlet tube (9a), the discharge (24b) of the oil pumping means (20) being maintained in fluid communication with the cylinder compression chamber (2) through a compressed refrigerant gas conduit (26a). Thus, the oil is drawn from the bottom of shell and pumped jointly with the refrigerant gas arriving to the pump discharge, through the heat exchanger (10) and returned to the inside of the shell (1).

BACKGROUND OF THE INVENTION 
The present invention relates to a hermetic compressor and, more 
particularly, to a joint gas and oil cooling system for a compressor of 
that type, used in small refrigeration and air conditioning systems. 
The hermetic compressors, particularly rotary ones, must be provided with 
means to cool the electric motor during operation of the unit, order to 
prevent degradation of the windings insulation and the consequent damage 
to the electric motor, and with means to cool the lubricant oil, so that 
it does not warm up excessively thereby degrading and loosing its 
lubricant properties. 
One of the known means to cool the electric motor consists in making the 
heated refrigerant gas that comes from the compressor discharge to pass 
through a heat exchanger or pre-cooler to be cooled therein and then to 
return to the inside of the compressor shell so as to cool the electric 
motor before being pumped to the refrigeration system. 
In spite of cooling the motor, the above mentioned system of the prior art 
does not cool the lubricant oil. A means employed to perform the joint 
cooling of gas and oil is described on the patent document U.S. Pat. No. 
4,569,645. That document describes a rotary compressor that comprises: a 
compression chamber; a main bearing and a secondary bearing; a rolling 
piston that rotates eccentrically, driven by an eccentric shaft inside the 
compression chamber, defining a high pressure chamber and a low pressure 
chamber, these elements being assembled inside a sealed shell in the lower 
portion of which is accumulated the lubricant oil that returns to the 
shell after being cooled in a heat exchanger external to the shell. During 
operation of the above mentioned set, the refrigerant gas is compressed 
and discharged through an ejector tube into a larger-diameter oil feed 
pipe that is in fluid communication with the lubricant oil stored inside 
the shell and is connected to the heat exchanger through an extension 
external to the shell. On being discharged in the oil feed pipe, the 
refrigerant gas carries the lubricant oil with it, making it circulate 
through the heat exchanger, where the oil and the refrigerant gas are 
cooled. 
An operational drawback of the previous solution shown above becomes 
evident at each new start-up of the compressor, when connected to a 
refrigeration system. As the oil intake is done below the level of the 
sump, during compressor stops the oil will accumulate in the initial 
portion of heat exchanger, thereby causing an obstruction to the normal 
circulation of the gas that should be pumped after each new startup of the 
compressor. 
This periodical pressure loss will, as a consequence, increase the daily 
power consumption of the refrigeration system. Another drawback of this 
previous technical solution results fron the manner whereby the oil is 
collected from the sump. Since the collection is done by drag, the gas 
ends up being quite diluted in the oil, causing foaming and bubbling, 
reducing the oil viscosity with a resulting decrease in its lubricant 
properties and its ability of acting as a sealant against compressed gas 
leakage between the movable parts inside the cylinder, from the 
compression chamber to the suction chamber. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a joint gas and oil 
cooling system for a hermetic compressor that eliminates the above 
mentioned drawbacks related to the solutions of the prior art. 
It is also an object of the present invention to provide a cooling system 
of the considered type that is easy to assemble the compressor and of a 
low additional cost.

In accordance with said illustration, the hermetic rotary compressor 
comprises a hermetic shell 1 with the lower portion thereof defining the 
lubricant oil sump and its inner portion housing a cylinder 2 frontally 
closed by the flanged portions 3 and 4 of a main bearing 3a and a 
subbearing 4a that support a horizontal crankshaft 5, which is fastened to 
the rotor of an electric motor 6 driving a rolling piston 7 inside 
cylinder 2. 
The illustrated compressor also includes a tube 8a for admission of 
refrigerant gas inside the cylinder, a tube 8b for gas discharge from the 
shell, a tube 9a for lubricant oil discharge, a tube 9b for lubricant oil 
return to the inside of shell 1 and a heat exchanger 10 of any appropriate 
construction, external to shell 1 and having its lubricant oil inlet and 
outlet connected to the tubes 9a and 9b respectively for lubricant oil 
discharge and return. 
In the illustrated configuration of the invention, the horizontal 
crankshaft 5 incorporates an oil pump 20, which assumes the shape of a 
cylindrical and eccentric portion 21, located in a medium point in the 
extension of crankshaft 5. The cylindrical and eccentric portion 21 is 
arranged so as to slide inside a cylindrical housing 22, concentrical to 
the axis of crankshaft 5 and provided--in the illustrated example--by a 
recess in the main bearing 3a. 
As illustrated or FIG. 2, the oil pump 20 is provided with a blade element 
23 which is attached by one of its ends to the internal cylindrical 
surface of the cylindrical housing 22 for the purpose of separating the 
intake chamber 24a and discharge chamber 24b of pump 20. 
Intake chamber 24a is connected to the oil sump of the shell 1 by means of 
a suction channel 25, which is made through the flanged portion 3 of the 
main bearing 3a. The discharge chamber 24b is connected to the oil 
discharge hole 26 by means of an oil discharge channel 27 made radially 
through the eccentric portion 21 of crankshaft 5. 
The end of the crankshaft 5 is provided with a rotating tubular fitting 28 
that interconnects the discharge hole 26 to the internal extension of the 
oil outlet tube of shell 1. The oil tubes 9a and 9b are connected to the 
heat exchanger 10 through appropriate pipes, represented on FIG. 1 through 
a pair of lines that represent the joint flow of gas and lubricant oil 
through the heat exchanger. 
The compressor also includes a muffler 11 assembled in the flanged portion 
4 of the sub-bearing 4a. That chamber receives the compressed gas from the 
cylinder 2 of the compressor, being in fluid communication with the 
longitudinal hole 26 for oil discharge through the corresponding extreme 
extension 26a of said hole. 
With the above described constructive arrangement, the lubricant oil is 
drawn upwardly from the bottom of shell 1, through the suction channel 25 
and, by action of pump 20, is pumped through the discharge channel 26, the 
oil outlet tube 9a, the heat exchanger 10 and the return tube 9b, to be 
stored again in the bottom of shell 1. 
Simultaneously, the refrigerant gas compressed in cylinder 2 is conveyed to 
the muffler 11 and from there to the oil discharge hole 26 through its 
extension 26a. Upon crossing the discharge hole 26, the flow of compressed 
refrigerant gas joins the oil flow so as to have the same path of the oil 
through the heat exchanger 10 and back to the inside of shell 1. In the 
illustrated arrangement of a hermetic rotary horizontal shaft compressor, 
an operational advantage is also obtained by reason of the existence of 
the discharge hole 26 made through the crankshaft 5. As the shaft rotates, 
the joint flow of gas and lubricant oil through the hole 26 is submitted 
to an oil - gas separation action. This separation effect allows the 
lubricant oil to maintain its viscosity characteristics, preserving its 
lubrication ability and allowing it to act as a sealant against fluid 
leakages from the compression chamber to the suction chamber in the 
cylinder between the movable parts of the unit. 
FIG. 1 illustrates a lubricant oil return tube 9b positioned so that the 
oil cooled in the heat exchanger is sprinkled over the electric motor upon 
its return to the inside of the shell. Notwithstanding the application of 
the new cooling system in a hermetic, rotary, horizontal shaft compressor 
has been described and illustrated herein, it should be understood that 
the constructive solution in question can be used in hermetic rotary 
vertical-shaft compressors and in hermetic compressors of the 
reciprocating piston type, merely by changing the position of the pump 
along the crankshaft and the lubricant oil suction and discharge tubes. It 
should also be understood that even through the present description has 
been done considering a specific type of oil pump, the invention is not 
limited to the utilization of that type of pump, since the technical 
effects thereof are equally achieved with pumps of the most varied 
construction types.