Scroll type fluid machine having a circulation path and inlet path for guiding refrigerant from a discharge chamber to a drive casing and to a rear-side of movable scroll

1. A scroll-type fluid machine comprising:

a housing including a drive casing and a compression casing air-tightly connected to said drive casing;

a rotary shaft rotatably supported in said drive casing through a bearing;

a scroll unit accommodated in said compression casing, said scroll unit having a movable scroll for carrying out a series of processes including suction, compression, and discharge of a refrigerant in cooperation with a fixed scroll by being driven by said rotary shaft to make a revolution of said movable scroll;

a discharge chamber defined in said compression casing, for causing the refrigerant adjusted to prescribed discharge pressure by a discharge valve to feed from said scroll unit to a refrigerant circuit;

a circulation path for introducing the refrigerant in said discharge chamber from the refrigerant circuit into said drive casing while maintaining the refrigerant pressure; and

an inlet path formed in said compression casing, for leading the refrigerant in said circulation path to a rear side of said movable scroll to make a pressure of the led refrigerant counteract the refrigerant discharge pressure acting on a front side of said movable scroll.

2. The scroll-type fluid machine according to claim 1 , including:

a machine chamber defined in said drive casing, said machine chamber having a motor for driving said rotary shaft when said motor is supplied with electricity; and

pressure control means for controlling the pressure of the refrigerant introduced from said circulation path toward the machine chamber and received on the rear side of said movable scroll in order to adjust balance with the refrigerant discharge pressure acting on the front side of the movable scroll.

3. The scroll-type fluid machine according to claim 2 , wherein:

said drive casing has a refrigerant inlet hole through which the refrigerant in said circulation path is introduced toward said machine chamber; and

the pressure control means is arranged either in said circulation path or in said refrigerant inlet hole.

4. The scroll-type fluid machine according to claim 3 , wherein:

said refrigerant inlet hole receives the refrigerant from a gas cooler in said refrigerant circuit to be introduced into said machine chamber.

5. The scroll-type fluid machine according to claim 2 , including:

a second circulation path for leading out the refrigerant in said machine chamber from said machine chamber toward said refrigeration circuit, wherein:

the refrigerant in said machine chamber is led through the second circulation path to a low pressure-side circuit of said refrigeration circuit and is subsequently introduced to said scroll unit through a suction port formed in said compression casing.

6. The scroll-type fluid machine according to claim 5 , further including:

a second pressure control means for controlling the pressure of the refrigerant led out of said machine chamber toward said second circulation path in order to maintain the refrigerant pressure in said machine chamber at the prescribed pressure.

7. The scroll-type fluid machine according to claim 6 , wherein:

said drive casing has a refrigerant outlet hole through which the refrigerant in said machine chamber is led out and directed toward said second circulation path; and said second pressure control means is arranged either in said refrigerant outlet hole or in said second circulation path.

8. The scroll-type fluid machine according to claim 7 , wherein:

the refrigerant in said machine chamber is led out through said refrigerant outlet hole and directed toward an internal heat exchanger inserted in said refrigeration circuit.

9. The scroll-type fluid machine according to claim 7 , wherein:

the refrigerant in said machine chamber is led out through the refrigerant outlet hole and directed toward an evaporator inserted in said refrigeration circuit.

10. The scroll-type fluid machine according to claim 1 , wherein:

the refrigerant contains lubricating oil; and the lubricating oil separated from the refrigerant in said discharge chamber is introduced to the bearing through a communication path formed in said compression casing.

11. The scroll-type fluid machine according to claim 1 , wherein:

the refrigerant is a CO 2 refrigerant.