1. Field of the Invention
The present invention relates to a vacuum preventing device of a scroll compressor, and more particularly, to a vacuum preventing device of a scroll compressor capable of preventing vacuum in a compressor by flowing backward discharge gas of a discharge region into a suction region at the time of abnormal driving such as pump down or expansion valve blocking.
2. Description of the Conventional Art
Generally, a compressor is a device for converting mechanical energy into latent energy of a compression fluid, and is largely classified into a reciprocation compressor, a scroll compressor, a centrifugal compressor, and a vane compressor by compression methods.
The scroll compressor has a structure that gas is sucked, compressed, and discharged by using a rotation member like the centrifugal type and the vane type differently from the reciprocating type which uses a linear reciprocation of an piston.
FIG. 1 is a longitudinal section view showing an inner part of a scroll compressor in accordance with the conventional art.
As shown, the conventional scroll compressor comprises: a case 1 having a gas suction pipe SP and a gas discharge pipe DP; a main frame 2 and a sub frame (not shown) respectively installed at upper and lower portions of an inner circumference surface of the case 1; a driving motor 3 installed between the main frame 2 and the sub frame; a rotation shaft 4 engaged to a center portion of the driving motor 3 for transmitting a rotation force of the driving motor 3; an orbiting scroll 5 installed to have an eccentric rotation at an upper portion of the rotation shaft 4 and having a wrap 5a of an involute curve shape at the upper portion thereof; and a fixed scroll 6 fixed to an upper portion of the main frame 2, engaged to the orbiting scroll 5, and having a wrap 6a of an involute curve shape so as to form a plurality of compression spaces P therein.
The case 1 is divided into a suction region S1 and a discharge region S2 by a high and low pressure separation plate 7.
A gas inlet 6b and a gas outlet 6c are respectively formed at a lateral surface and a center portion of the fixed scroll 6, and a non-return valve 8 for preventing discharged gas from flowing backward is installed at an upper surface of the fixed scroll 6.
The main frame 2 and the sub frame are fixed to the inner circumference surface of the case 1 by a fixation means such as welding, and the fixed scroll 6 is also fixed to a lower surface of the high and low pressure separation plate 7 by a fixation means such as a bolt.
Meantime, in case of a pump down and an expansion valve blocking, the suction region S1 of the compressor becomes a high vacuum state. At this time, components of the compressor may be damaged and destroyed.
To prevent this, in the conventional art, a vacuum preventing device 9 is provided in the body 6A of the fixed scroll 6.
FIG. 2 is a longitudinal section view showing an operation of the conventional vacuum preventing device at the time of a normal driving, and FIG. 3 is a longitudinal section view showing an operation of the conventional vacuum preventing device at the time of an abnormal driving.
Referring to FIGS. 2 and 3, the conventional vacuum preventing device 9 comprises a pressure space 10 formed in the fixed scroll 6, and a discharge flow path 11 connected to the discharge region S2 at an upper surface of the pressure space 10.
A compression flow path 12 connected to a compression chamber is formed at a lower surface of the pressure space 10, a plug 14 having a suction flow path 13 is fixed to an opening portion of the pressure space 10 by a fixation pin 15, and the suction flow path 13 is connected to the discharge flow path 11.
A piston 17 for selectively connecting the discharge flow path 11 and the suction flow path 13 is movably installed in the pressure space 10.
A spring 16 for limiting a movement of the piston 17 and providing an elasticity force thereto is installed at the opening portion of the pressure space 10.
Hereinafter, operations of the conventional scroll compressor will be explained.
First, when a power source is applied to the driving motor 3, the driving motor 3 rotates the rotation shaft 4, and the orbiting scroll 5 engaged to the rotation shaft 4 is rotated to an extent of its eccentric distance.
At this time, the plurality of compression spaces P formed between the wrap 5a of the orbiting scroll 5 and the wrap 6a of the fixed scroll 6 gradually move towards a center portion of the fixed scroll 6 as the orbiting scroll 5 continuously performs an orbiting movement, thereby decreasing in volume.
By the decreased volume of the compression spaces P, gas of the suction region S1 is sucked into the compression spaces P through the inlet 6b, and the sucked gas is discharged to the discharge region S2 through the gas outlet 6c. 
When the compressor is normally driven, a pressure of the compression chamber is larger than an elasticity force of the spring 16, so that the piston 17 overcomes the elasticity force of the spring 16 and blocks the discharge flow path 11.
However, when the compressor is abnormally driven due to a pump down or an expansion valve blocking, inside of the compression chamber becomes vacuum and a pressure of the compression chamber P becomes smaller than the elasticity force of the spring 16, so that the piston 17 is shoved by the elasticity force of the spring 16 and opens the discharge flow path 11. At this time, the discharge flow path 11 is connected to the suction flow path 13.
As the discharge flow path 11 and the suction flow path 13 are connected to each other, gas of the discharge region S2 flows backward into the suction region S1 through the discharge flow path 11 and the suction flow path 13, thereby releasing the vacuum in the compressor.
However, in the conventional art, since the vacuum preventing device is formed in the fixed scroll, a fabrication cost of the vacuum preventing device is too expensive and an intensity of the fixed scroll is degraded. According to this, the fixed scroll is easily damaged during operation.
Also, since the pressure space is formed at the lateral surface of the fixed scroll and the plug has to be inserted to an end of the opening portion of the pressure space in order to prevent the spring and the piston installed in the pressure space from being separated, an entire construction becomes complicated and a fabrication cost is increased.