Scroll fluid machine having scroll members at each end of a rotating hollow shaft

A scroll fluid machine comprising:

• a stationary member including a casing and two fixed scroll members fixedly provided in said casing at both ends of said casing, said two fixed scroll members being centered on an axis of said casing, each of said fixed scroll members having a spiral wrap portion standing on an end plate;
• an electric motor provided in said casing between said two fixed scroll members, said electric motor having a rotor and a stator which are so arranged that their axes extend parallel with the axis of said casing;
• two eccentric bearings provided in association with said two fixed scroll members, each of said two eccentric bearings including an outer ring provided between said electric motor and the fixed scroll member associated therewith and fixedly fitted at an outer periphery thereof to said casing, and an intermediate ring rotatably provided at an inner peripheral side of said outer ring, an inner periphery of said intermediate ring having an eccentric axis radially displaced relative to an axis of said outer ring, each of said eccentric bearings further including an inner ring rotatably provided at an inner peripheral side of said intermediate ring, said inner ring being rotatable about said eccentric axis;
• a rotating shaft formed from a hollow shaft member extending between the intermediate rings of said two eccentric bearings through the rotor of said electric motor, said rotating shaft being rotatable together with said intermediate rings as one unit by said rotor;
• an orbiting shaft loosely fitted in said rotating shaft, an axis of said orbiting shaft being coincident with said eccentric axis, said orbiting shaft being fixedly supported by the inner rings of said two eccentric bearings so as to perform an orbiting motion together with said inner rings as one unit;
• two orbiting scroll members connected to both ends of said orbiting shaft to face said fixed scroll members, respectively, each of said orbiting scroll members having a spiral wrap portion standing on an end plate so as to overlap the wrap portion of the fixed scroll member associated therewith to define a plurality of compression chambers;
• and
• a rotation preventing mechanism provided between at least either one of said two orbiting scroll members and said stationary member to prevent rotation of said orbiting scroll members,
• wherein each end plate of said fixed scroll members includes a back-pressure bore, and each end plate and back-pressure bore of the fixed scroll members and a portion of said casing define a pressure chamber, and
• wherein each of the back-pressure bores is positioned so that each of the compression chambers communicates with the corresponding pressure chamber when the compression chamber reaches an intermediate position during the course of movement from a radially outermost position to a radially innermost position such that an intermediate pressure is established in each of the pressure chambers.