1. Field of the Invention
The present invention relates to a scroll type fluid machine, and more particularly, to a scroll type compressor suitably used as a refrigerant compressor of an air conditioner and a refrigerator, and as an air compressor.
2. Description of the Related Art
In a conventional scroll type compressor, a fixed scroll member and an orbiting scroll member, each composed of an end plate and a scroll wrap portion standing perpendicular to the end plate, are meshed with the wrap portions inside and the orbiting scroll member is driven by a main shaft directly connected to a motor or the like to make revolution, by which refrigerant gas is sucked into a compression chamber formed by both the scroll members, the compression chamber is moved to a central portion to reduce the volume thereof and increase the pressure therein, and the refrigerant gas is exhausted from a discharge port in the central portion therein.
In such a scroll type compressor, compression is performed by meshing both the scroll wrap portions with each other, and setting of the positions of these wrap portions in the vertical direction is considerably important. If wider spaces than needed are formed between the leading ends of the wrap portions and the opposed end plates, the refrigerant gas leaks from the spaces to the low pressure side, thereby lowering the performance of the compressor. Furthermore, if the leading ends of the wrap portions are in excessively strong contact with the corresponding end plates, galling and wear are caused and interfere with smooth compression.
Still further, since the gas in the compression chamber has a force which separates the scroll members from each other in the axial direction, there is provided a mechanism for keeping, against this separating force, both the scroll members in tight contact or slightly spaced.
For example, Japanese Patent Unexamined Publication No. 63-80088 discloses a closed scroll type compressor which increases the pressure of a refrigerant gas, led into a hermetic case, by compression and directly discharges the refrigerant gas to the outside of the hermetic case. In this compressor, a thrust bearing is provided in the rear of an end plate in an orbiting scroll member, a fixed scroll member is fixed to the hermetic case through a pair of leaf springs, and an airtight chamber is formed in the rear of the fixed scroll member. Gas pressure is applied to the airtight chamber to slightly move the fixed scroll member in the axial direction thereof, and to minimize the space between wrap portions of the scroll members, by which leakage of a compression chamber can be prevented.
However, in such a structure, the whole thrust force in the axial direction applied to the orbiting scroll member by compressing the refrigerant gas acts on the thrust bearing. Furthermore, when the fixed scroll member is slightly moved toward the orbiting scroll member against the spring force of the leaf springs by exerting the gas pressure on the rear of the fixed scroll member, a force, which is obtained from deducting a reaction force of the leaf springs from the gas pressure applied to the rear of the fixed scroll member, further presses the orbiting scroll member in the axial direction, and therefore, the thrust bearing receives greater force.
Accordingly, an expensive thrust bearing resistant to a heavy thrust load is needed, and frictional force is caused by the slide between the thrust bearing and the rear of the end plate in the orbiting scroll member, which results into large sliding loss, lowered efficiency of the compressor, and abrasion, burning and the like of the aforesaid sliding portion.
Further, in such a structure, a complicated structure is required to move the fixed scroll member in the axial direction, to avoid excessive contact and abutment between the wrap portions of the fixed scroll member and the orbiting scroll member, and to prevent the displacement of center shafts and phases of both the scroll wrap portions. This causes various problems, for example, decrease in productivity and decrease in efficiency and reliability owing to excessive contact.