In general, a compressor is a mechanical apparatus for compressing the air, refrigerant or other various operation gases and raising a pressure thereof, by receiving power from a power generation apparatus such as an electric motor or turbine. The compressor has been widely used for an electric home appliance such as a refrigerator and an air conditioner, or in the whole industry.
The compressors are roughly classified into a reciprocating compressor in which a compression space for sucking or discharging an operation gas is formed between a piston and a cylinder, and the piston is linearly reciprocated inside the cylinder, for compressing a refrigerant, a rotary compressor in which a compression space for sucking or discharging an operation gas is formed between an eccentrically-rotated roller and a cylinder, and the roller is eccentrically rotated along the inner wall of the cylinder, for compressing a refrigerant, and a scroll compressor in which a compression space for sucking or discharging an operation gas is formed between an orbiting scroll and a fixed scroll, and the orbiting scroll is rotated along the fixed scroll, for compressing a refrigerant.
Recently, a linear compressor which can improve compression efficiency and simplify the whole structure without a mechanical loss resulting from motion conversion by connecting a piston directly to a linearly-reciprocated driving motor has been popularly developed among the reciprocating compressors.
In the linear compressor, the piston is linearly reciprocated in a cylinder by a linear motor inside a hermetic shell, for sucking, compressing and discharging a refrigerant. An oil supply apparatus for pumping the oil stored at the lower portion of the shell into a gap between the cylinder and the piston is provided to perform cooling and lubrication against the friction generated when the piston is linearly reciprocated inside the cylinder.
FIG. 1 is a cross-sectional view illustrating a conventional oil supply apparatus of a linear compressor.
Referring to FIG. 1, the conventional oil supply apparatus of the linear compressor is installed at a lower portion of a structure 1 disposed inside a hermetic shell (not shown) and comprised of a cylinder 2, a piston 4 and a linear motor (not shown). An oil supply passage 12 and an oil recovery passage 14 are formed in one side main body frame 3 to communicate with an oil circulation passage 10 formed between the cylinder 2 and the piston 4. A mass member 24 is elastically supported by oil springs 26a and 26b in an oil cylinder 22 formed at the lower portion of the oil supply passage 12 to communicate with the oil supply passage 12, and linearly reciprocated to generate a pressure difference. An oil supply tube 21 soaked in the oil stored at the lower portion of the shell is installed at one side of the oil cylinder 22 to communicate with the oil cylinder 22. An oil supply valve assembly 28 for controlling oil supply is installed between the oil supply passage 12 and the oil cylinder 22.
The main body frame 3 fixes the cylinder 2 and the linear motor. The piston 4 is linearly reciprocated between a top dead center (TDC) and a bottom dead center (BDC) inside the cylinder 2, for repeatedly performing a suction stroke for sucking a refrigerant into a compression space P formed between the piston 4 and the cylinder 2, and a compression stroke for compressing and discharging the refrigerant. A suction valve 6 for sucking the refrigerant is installed at an end of the piston 4, and a discharge valve 8a for discharging the compressed refrigerant is elastically supported and opened and closed by a discharge valve spring 8c inside a discharge cap 8b fixed to an end of the cylinder 2.
The oil supply passage 12 and the oil recovery passage 14 are formed in the main body frame 3 and the cylinder 2, for supplying and recovering the oil to/from the oil circulation passage 10 formed between the cylinder 2 and the piston 4. The oil circulation passage 10 is formed by a ring-shaped cylinder groove 2h of the inner circumference of the cylinder 2 and a ring-shaped piston groove 4h of the outer circumference of the piston overlapped with each other, for circulating the oil.
The oil cylinder 22 communicates with the end of the oil supply passage 12 at the lower portion of the structure 1 to be vibrated with the structure 1. The mass member 24 is linearly reciprocated inside the oil cylinder 22 due to an inertia force to the vibration of the oil cylinder 22. The oil springs 26a and 26b elastically support both ends of the mass member 24 in the axial direction, and generate the pressure difference in the oil cylinder 22. The oil supply tube 21 is installed at the lower portion of the oil cylinder 22 to communicate with the oil cylinder 22. The end of the oil supply tube 21 is soaked in the oil stored at the shell. In detail, an end of the oil cylinder 22 is fixedly inserted into a fixing groove 3h steppedly formed at the bottom end of the main body frame 3 communicating with the oil supply passage 12. A fixing cap 27 is forcibly inserted into the other end of the oil cylinder 22. Both ends of the mass member 24 are elastically supported by the oil springs 26a and 26b between the stepped fixing groove 3h of the oil supply passage 12 and the fixing cap 27, respectively. Here, an end of the fixing cap 27 is forcibly inserted into the other end of the oil cylinder 22, and the other end thereof is caught on the other end of the oil cylinder 22. That is, the fixing cap 27 is double stepped to be elastically supported by the oil spring 26a. A through hole 27h is formed at the center portion of the fixing cap 27. Accordingly, although the mass member 24 is linearly reciprocated in the oil cylinder 22, one side inner space of the oil cylinder 22 maintains the same pressure as the pressure inside the shell without a pressure difference.
The oil supply valve assembly 28 includes a plate-shaped valve sheet 28a installed at one side of the main body frame 3 communicating with the oil cylinder 22 and the oil supply passage 12, an oil suction valve (not shown) for sucking the oil and an oil discharge valve (not shown) for discharging the oil being installed on the valve sheet 28a to be opened and closed, and a sheet cover 28b installed outside the valve sheet 28a to overlap with the valve sheet 28a, for forming a suction storage space A and a discharge storage space B for temporarily storing the oil. Various components such as a gasket are additionally installed between the valve sheet 28a and the sheet cover 28b, for preventing leakage of the oil. In the conventional oil supply apparatus, when the oil cylinder 22 is vibrated with the structure 1, the mass member 24 is linearly reciprocated inside the oil cylinder 22 die to the inertia force to generate the pressure difference at one side inner space of the oil cylinder 22. Therefore, the oil stored at the lower portion of the shell is sucked into the oil supply tube 21, passed through the oil supply valve assembly 28a and 28b, supplied through the oil supply passage 12, circulated along the oil circulation passage 10 for cooling and lubrication, and recovered to the lower portion of the shell through the oil recovery passage 14.
The conventional oil supply apparatus of the linear compressor supplies the oil by vibration generated by an operating frequency of the main body frame 3 by linear reciprocation of the piston 4. When a natural frequency according to the oil springs 26a and 26b and the mass member 24 exists in a specific band, the mass member 24 is excessively moved to abrade support portions of the oil springs 26a and 26b. 