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

Abstract

A scroll fluid machine requiring no crank shaft to orbitably support an orbiting scroll member and capable of being reduced in overall size in the axial direction. In a casing, two fixed scroll members are provided on the axis of the casing, and an electric motor is provided between the fixed scroll members. Eccentric bearings each having an outer ring, an intermediate ring and an inner ring are provided between the electric motor and the fixed scroll members. The inner periphery of each intermediate ring is formed with an axis eccentric with respect to the axis of the casing. Orbiting scroll members are integrated with the inner rings through an orbiting shaft. The orbiting shaft is caused to orbit by rotating a rotating shaft with the electric motor, thereby causing the orbiting scroll members to orbit relative to the fixed scroll members.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a scroll fluid machine suitable for use in an air compressor, a vacuum pump, etc. by way of example.

In general, a scroll fluid machine has a casing and a fixed scroll member provided in the casing. A driving shaft is rotatably provided in the casing. An orbiting scroll member is orbitably provided on the distal end of the driving shaft in the casing to come in sliding contact with the fixed scroll member in the axial direction. A plurality of compression chambers are defined between the orbiting scroll member and the fixed scroll member [for example, see Japanese Patent Application Unexamined Publication (KOKAI) Nos. 6-26484 (1994) and 9-144674 (1997)].

In this type of conventional scroll fluid machine, the driving shaft is externally driven to rotate, causing the orbiting scroll member to perform an orbiting motion with a predetermined eccentricity with respect to the fixed scroll member, thereby sucking a fluid, e.g. air, from a suction opening provided at the outer periphery of the fixed scroll member, and successively compressing the fluid in the compression chambers formed between the wrap portions of the fixed and orbiting scroll members. Finally, the compressed fluid is discharged to the outside from a discharge opening provided in the center of the fixed scroll member.

Incidentally, in the above-described conventional scroll fluid machine, a crank shaft is provided at the distal end of the driving shaft at a position eccentric with respect to the axis of the driving shaft to orbitably support the orbiting scroll member at the distal end of the driving shaft. The crank shaft is integral with the driving shaft or provided as a member separate from the driving shaft.

Accordingly, the overall length of the driving shaft becomes extra longer by the length of the crank shaft. This causes the whole apparatus to increase in size in the axial direction unfavorably.

In view of the above-described problems with the prior art, an object of the present invention is to provide a scroll fluid machine designed to eliminate the need for a crank shaft for orbitably supporting an orbiting scroll member and to enable a reduction in overall length in the axial direction.

SUMMARY OF THE INVENTION

To attain the above-described object, the present invention provides a scroll fluid machine arranged as stated below.

The scroll fluid machine includes a stationary member having a casing and two fixed scroll members fixedly provided in the casing at both ends of the casing. The two fixed scroll members are centered on the axis of the casing. Each of the fixed scroll members has a spiral wrap portion standing on an end plate. An electric motor is provided in the casing between the two fixed scroll members. The electric motor has a rotor and a stator which are so arranged that their axes extend parallel with the axis of the casing. Two eccentric bearings are provided in association with the two fixed scroll members. Each of the two eccentric bearings includes an outer ring provided between the electric motor and the associated fixed scroll member and fixedly fitted at the outer periphery thereof to the casing. An intermediate ring is rotatably provided at the inner peripheral side of the outer ring. The inner periphery of the intermediate ring has an eccentric axis radially displaced relative to the axis of the outer ring. An inner ring is rotatably provided at the inner peripheral side of the intermediate ring. The inner ring is rotatable about the eccentric axis. A rotating shaft is provided to extend between the intermediate rings of the two eccentric bearings through the rotor of the electric motor. The rotating shaft is formed from a hollow shaft member and rotatable together with the intermediate rings as one unit by the rotor. An orbiting shaft is loosely fitted in the rotating shaft. The axis of the orbiting shaft is coincident with the eccentric axis. The orbiting shaft is fixedly supported by the inner rings of the two eccentric bearings so as to perform an orbiting motion together with the inner rings as one unit. Two orbiting scroll members are connected to both ends of the orbiting shaft to face the fixed scroll members, respectively. Each of the orbiting scroll members has a spiral wrap portion standing on an end plate so as to overlap the wrap portion of the associated fixed scroll member to define a plurality of compression chambers. In addition, a rotation preventing mechanism is provided between at least either one of the two orbiting scroll members and the stationary member to prevent rotation of the orbiting scroll members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a scroll air compressor according to a first embodiment of the present invention.

FIG. 2 is an enlarged fragmentary sectional view of a fixed scroll member, an eccentric bearing, a rotating shaft, an orbiting scroll member, etc. in the scroll air compressor shown in FIG. 1 .

FIG. 3 is a sectional view showing the eccentric bearing in FIG. 2 in the form of a single element.

FIG. 4 is a sectional view as seen in the direction of the arrow IV—IV in FIG. 3 .

FIG. 5 is an enlarged sectional view showing the rotating shaft in FIG. 1 in the form of a single element.

FIG. 6 is a sectional view as seen in the direction of the arrow VI—VI in FIG. 5 .

FIG. 7 is a longitudinal sectional view of a scroll air compressor according to a second embodiment of the present invention.

FIG. 8 is a longitudinal sectional view of a scroll air compressor according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A scroll fluid machine according to a first embodiment of the present invention will be described below in detail with reference to the accompanying drawings. In the first embodiment, the present invention is applied to a scroll air compressor as an example of scroll fluid machines.

FIGS. 1 to 6 show the first embodiment of the present invention. A cylindrical casing 1 forms an outer frame of a scroll air compressor. As shown in FIG. 1 , the casing 1 has a cylindrical portion 2 with an axis O 1 —O 1 . Left and right cover portions 3 A and 3 B cover both ends of the cylindrical portion 2 . The casing 1 constitutes a stationary member in combination with fixed scroll members 4 A and 4 B.

The fixed scroll members 4 A and 4 B are provided on the inner peripheral side of the cylindrical portion 2 at respective (left and right) axial ends of the casing 1 . As shown in FIG. 1 , one fixed scroll member 4 A has an end plate 5 A formed in an approximately disk-like shape. The end plate 5 A is positioned so that the center thereof is coincident with the axis O 1 —O 1 of the casing 1 . A spiral wrap portion 6 A is provided on the front side of the end plate 5 A. In addition, a fitting cylindrical portion 7 A projects axially from the outer peripheral edge of the end plate 5 A in the same direction as the direction in which wrap portion 6 A projects. The fitting cylindrical portion 7 A is fixedly fitted to the inner periphery of the cylindrical portion 2 .

The other fixed scroll member 4 B similarly has an end plate 5 B, a wrap portion 6 B and a fitting cylindrical portion 7 B.

An electric motor 8 is provided in the middle of the casing 1 between the fixed scroll members 4 A and 4 B. The electric motor 8 has a stator 9 fixedly provided on the inner periphery of the casing 1 . A rotor 10 is disposed at the inner peripheral side of the stator 9 so as to be rotatable by the stator 9 . The axes of both the stator 9 and the rotor 10 are coincident with the axis O 1 —O 1 of the casing 1 .

Left and right thrust bearings 11 A and 11 B are provided at the inner peripheral side of the casing 1 between the electric motor 8 and the fixed scroll members 4 A and 4 B, respectively. One thrust bearing 11 A has a mounting cylinder 12 A rigidly attached to the inner periphery of the cylindrical portion 2 of the casing 1 . An annular projection 13 A projects radially inward from the mounting cylinder 12 A at the rear side of an end plate 23 A of an orbiting scroll member 22 A (described later). The thrust bearing 11 A bears a thrust load acting on the orbiting scroll member 22 A and also forms grooves of an Oldham's ring (described later).

The other thrust bearing 11 B similarly has a mounting cylinder 12 B and an annular projection 13 B.

Left and right eccentric bearings 14 A and 14 B are provided on the inner peripheral sides of the thrust bearings 11 A and the 11 B at respective positions between the electric motor 8 and the fixed scroll members 4 A and 4 B. As shown in FIGS. 2 to 4 , one eccentric bearing 14 A has an outer ring 15 A and an intermediate ring 17 A rotatably provided at the inner peripheral side of the outer ring 15 A through a plurality of needle rollers 16 A. In addition, an inner ring 19 A is rotatably provided at the inner peripheral side of the intermediate ring 17 A through a plurality of needle rollers 18 A.

The outer ring 15 A is press-fitted at the outer periphery thereof to the inner periphery of the mounting cylinder 12 A of the thrust bearing 11 A. Thus, the axes of both the inner and outer peripheries of the outer ring 15 A are coincident with the axis O 1 —O 1 .

The intermediate ring 17 A is positioned at the inner peripheral side of the outer ring 15 A by the needle rollers 16 A. Thus, the axis of the outer periphery of the intermediate ring 17 A is coincident with the axis O 1 —O 1 of the outer ring 15 A. Consequently, the intermediate ring 17 A rotates about the axis O 1 —O 1 .

The intermediate ring 17 A has an axial bore 17 A 1 for accommodating the inner ring 19 A, and the accommodating bore 17 A 1 has an eccentric axis O 2 —O 2 that is radially displaced relative to the axis O 1 —O 1 of the outer ring 15 A by a predetermined dimension a. In addition, the inner periphery of the intermediate ring 17 A is formed with a mounting step portion 17 A 2 to which a rotating shaft 20 (described later) is secured. The axis of the mounting step portion 17 A 2 is coincident with the axis O 1 —O 1 .

The inner ring 19 A is positioned at the inner peripheral side of the intermediate ring 17 A by the needle rollers 18 A. Thus, the axes of both the inner and outer peripheries of the inner ring 19 A are coincident with the eccentric axis O 2 —O 2 . Consequently, the inner ring 19 A rotates about the eccentric axis O 2 —O 2 .

Thus, in the eccentric bearing 14 A, the intermediate ring 17 A is caused to rotate relative to the outer ring 15 A by the rotating shaft 20 , and this causes the inner ring 19 A to perform an orbiting motion with an orbiting radius ä about the axis O 1 —O 1 .

The other eccentric bearing 14 B similarly has an outer ring 15 B, needle rollers 16 B, an intermediate ring 17 B, needle rollers 18 B and an inner ring 19 B, and the intermediate ring 17 B is provided with an accommodating bore 17 B 1 and a mounting step portion 17 B 2 .

The rotating shaft 20 is provided to extend between the intermediate rings 17 A and 17 B of the eccentric bearings 14 A and 14 B. The rotating shaft 20 is formed in the shape of a hollow shaft member and fixedly fitted to the inner periphery of the rotor 10 of the electric motor 8 . Both ends of the rotating shaft 20 are rigidly secured to the respective mounting step portions 17 A 2 and 17 B 2 of the intermediate rings 17 A and 17 B. The rotating shaft 20 rotates together with the rotor 10 as one unit, thus causing the intermediate rings 17 A and 17 B to rotate.

As shown in FIG. 5 , the axis of the outer periphery of the rotating shaft 20 is coincident with the common axis O 1 —O 1 of the outer rings 15 A and 15 B, whereas the axis of the inner periphery of the rotating shaft 20 is coincident with the common eccentric axis O 2 —O 2 of the intermediate rings 17 A and 17 B. Accordingly, assuming that the wall thickness of a part of the rotating shaft 20 on the side of the axis O 1 —O 1 remote from the eccentric axis O 2 —O 2 is dl and the wall thickness of a part of the rotating shaft 20 on the side closer to the eccentric axis O 2 —O 2 is d 2 , the relationship between the two wall thicknesses is expressed by d 1 >d 2 .

An orbiting shaft 21 is loosely fitted in the rotating shaft 20 and fixedly supported by the inner rings 19 A and 19 B of the eccentric bearings 14 A and 14 B. The axis of the orbiting shaft 21 is coincident with the eccentric axis O 2 —O 2 . Both ends of the orbiting shaft 21 are fitted to the respective inner peripheries of the inner rings 19 A and 19 B and rigidly secured thereto. The orbiting shaft 21 performs an orbiting motion together with the inner rings 19 A and 19 B as one unit, thereby causing orbiting scroll members 22 A and 22 B (described later) provided on both ends of the orbiting shaft 21 to perform an orbiting motion.

As shown in FIG. 2 , the axial length L of the orbiting shaft 21 is set at a value approximately equal to or slightly greater than the distance between the annular projections 13 A and 13 B of the thrust bearings 11 A. Consequently, the front sides of the thrust bearings 11 A and 11 B and the rear sides of the associated end plates 23 A and 23 B of the orbiting scroll members 22 A and 22 B are in contact with each other or have a slight gap, for example, of about 10 micrometers therebetween.

Thus, both ends of the orbiting shaft 21 abut on the respective end plates 23 A and 23 B of the orbiting scroll members 22 A and 22 B to serve as a spacer for positioning the orbiting scroll members 22 A and 22 B with respect to the axial direction.

The left and right orbiting scroll members 22 A and 22 B are fixedly provided on the two axial ends of the orbiting shaft 21 to face the fixed scroll members 4 A and 4 B, respectively. As shown in FIGS. 1 and 2 , one orbiting scroll member 22 A has an end plate 23 A formed in a disk-like shape and a spiral wrap portion 24 A provided on the front side of the end plate 23 A to extend axially.

The end plate 23 A of the orbiting scroll member 22 A has a cylindrical projection 25 A projecting from the center of the rear side thereof. The cylindrical projection 25 A is fitted to the inner periphery of the orbiting shaft 21 and rigidly secured thereto. Thus, the orbiting scroll member 22 A performs an orbiting motion with an orbiting radius ä together with the orbiting shaft 21 as one unit. The orbiting scroll member 22 A is positioned so that the wrap portion 24 A overlaps the wrap portion 6 A of the fixed scroll member 4 A with an offset angle of 180 degrees, for example. Thus, a plurality of compression chambers 26 A are defined between the two wrap portions 6 A and 24 A.

During the operation of the scroll air compressor, air is sucked into the outermost compression chamber 26 A from a suction opening 32 A (described later), and the sucked air is successively compressed in the compression chambers 26 A during the orbiting motion of the orbiting scroll member 22 A. Finally, the compressed air is discharged from the central compression chamber 26 A to the outside through a discharge opening 33 A (described later).

The other orbiting scroll member 22 B similarly has an end plate 23 B, a wrap portion 24 B and a cylindrical projection 25 B, and a plurality of compression chambers 26 B are defined between the orbiting scroll member 22 B and the fixed scroll member 4 B.

Left and right back-pressure bores 27 A and 27 B are provided in the end plates 5 A and 5 B of the fixed scroll members 4 A and 4 B, respectively. One back-pressure bore 27 A communicates with an intermediate compression chamber 26 A between the outermost compression chamber 26 A, which is the closest to the suction opening 32 A, and the innermost compression chamber 26 A, which is the closest to the discharge opening 33 A. The back-pressure bore 27 A leads an intermediate pressure from the intermediate compression chamber 26 A to a pressure chamber 28 A (described later) as a back pressure. The other back-pressure bore 27 B is arranged as in the case of the back-pressure bore 27 A.

Left and right pressure chambers 28 A and 28 B are formed between the cover portions 3 A and 3 B of the casing 1 and the end plates 5 A and 5 B of the fixed scroll members 4 A and 4 B, respectively. One pressure chamber 28 A leads an intermediate pressure from the compression chambers 26 A to the rear side of the end plate 5 A through the back-pressure bore 27 A. With the intermediate pressure, the fixed scroll member 4 A is pressed axially toward the orbiting scroll member 22 A. The other pressure chamber 28 B is arranged as in the case of the pressure chamber 28 A.

O-rings 29 A and 29 B are provided between the casing 1 and the respective outer peripheries of the end plates 5 A and 5 B of the fixed scroll members 4 A and 4 B. The O-rings 29 A and 29 B provide hermetic sealing between the outermost compression chambers 26 A and 26 B and the pressure chambers 28 A and 28 B.

O-rings 30 A and 30 B are provided in respective areas between the central portions of the end plates 5 A and 5 B of the fixed scroll members 4 A and 4 B and the discharge openings 33 A and 33 B. The O-rings 30 A and 30 B provide hermetic sealing between the innermost compression chambers 26 A and 26 B and the pressure chambers 28 A and 28 B.

Oldham's rings 31 A and 31 B are provided between the thrust bearings 11 A and 11 B and the orbiting scroll members 22 A and 22 B, respectively, to serve as rotation preventing mechanisms. One Oldham's ring 31 A is guided in two orthogonal axis directions between the annular projection 13 A of the thrust bearing 11 A and the end plate 23 A of the orbiting scroll member 22 A, thereby preventing rotation of the orbiting scroll member 22 A. The other Oldham's ring 31 B is arranged as in the case of the Oldham's ring 31 A. The arrangement and operation of the Oldham's rings 31 A and 31 B per se are well known.

The suction openings 32 A and 32 B are provided in the cylindrical portion 2 of the casing 1 at respective positions facing the outer peripheries of the wrap portions 6 A and 6 B of the fixed scroll members 4 A and 4 B. The suction opening 32 A opens in the outermost compression chamber 26 A to lead the outside air into the compression chamber 26 A. The other suction opening 32 B is arranged as in the case of the suction opening 32 A.

The discharge openings 33 A and 33 B are provided in the cover portions 3 A and 3 B of the casing 1 at respective positions facing the centers of the wrap portions 6 A and 6 B of the fixed scroll members 4 A and 4 B. One discharge opening 33 A opens in the innermost compression chamber 26 A to discharge the compressed air, which has been compressed in the compression chambers 26 A, to the outside. The other discharge opening 33 B is arranged as in the case of the discharge opening 33 A.

The scroll air compressor according to this embodiment has the above-described arrangement. Next, the operation of the scroll air compressor will be described.

As the rotor 10 of the electric motor 8 rotates, the rotating shaft 20 , which is integral with the rotor 10 , performs a rotational motion. At this time, the intermediate rings 17 A and 17 B of the two eccentric bearings 14 A and 14 B, which are provided on both ends of the rotating shaft 20 , perform a rotational motion together with the rotating shaft 20 as one unit at the inner peripheral sides of the outer rings 15 A and 15 B.

The inner peripheries of the intermediate rings 17 A and 17 B of the eccentric bearings 14 A and 14 B have the common eccentric axis O 2 —O 2 , which is radially displaced relative to the common axis O 1 —O 1 of the outer rings 15 A and 15 B by the dimension ä. Therefore, as the intermediate rings 17 A and 17 B rotate about the axis O 1 —O 1 relative to the outer rings 15 A and 15 B as stated above, the inner rings 19 A and 19 B, which are provided at the inner peripheral sides of the intermediate rings 17 A and 17 B, perform an orbiting motion with an orbiting radius a about the axis O 1 —O 1 . Thus, the orbiting shaft 21 , which is integral with the inner rings 19 A and 19 B, causes the orbiting scroll members 22 A and 22 B to orbit.

When orbiting as stated above, the orbiting scroll members 22 A and 22 B are prevented from rotating by the respective Oldham's rings 31 A and 31 B. Thus, the orbiting scroll members 22 A and 22 B only revolve around the axis O 1 —O 1 .

Consequently, the compression chambers 26 A, which are defined between the fixed scroll member 4 A and the orbiting scroll member 22 A, are continuously contracted. Thus, the outside air sucked in from the suction opening 32 A of the fixed scroll member 4 A is successively compressed in the compression chambers 26 A, and the compressed air is discharged from the discharge opening 33 A of the fixed scroll member 4 A and stored in an external air tank or the like (not shown).

The compression chambers 26 B, which are defined between the fixed scroll member 4 B and the orbiting scroll member 22 B, are also continuously contracted. Thus, the outside air sucked in from the suction opening 32 B of the fixed scroll member 4 B is successively compressed in the compression chambers 26 B, and the compressed air is discharged from the discharge opening 33 B of the fixed scroll member 4 B and stored in the external air tank or the like.

Thus, in this embodiment, both ends of the orbiting shaft 21 are orbitably supported by the eccentric bearings 14 A and 14 B, whereby the orbiting scroll members 22 A and 22 B, which are integrally provided on the two ends of the orbiting shaft 21 , can be driven to orbit. Accordingly, it is possible to eliminate the need to additionally provide a crank shaft at each end of the orbiting shaft 21 , as stated in regard to the prior art, in order to cause the orbiting scroll members 22 A and 22 B to perform an orbiting motion. Thus, the whole apparatus can be reduced in size in the axial direction.

In addition, the scroll air compressor comprises two compression mechanisms consisting essentially of the fixed scroll members 4 A and 4 B and the orbiting scroll members 22 A and 22 B. Therefore, it is possible to reduce the number of turns of the wrap portions 6 A, 6 B, 24 A and 24 B in comparison to a compressor having the same capacity as that of the compressor according to the embodiment and comprising one compression mechanism consisting essentially of one set of scroll members as in the prior art. Accordingly, the whole apparatus can be reduced in size in the radial direction.

In addition, the axial length L of the orbiting shaft 21 is set so that the orbiting scroll members 22 A and 22 B and the front sides of the thrust bearings 11 A and 11 B are in contact with each other or have a slight gap therebetween. Accordingly, it is possible to reduce the sliding resistance acting between the thrust bearings 11 A and 11 B and the orbiting scroll members 22 A and 22 B during the compression operation and hence possible to prevent the sliding surfaces of these members from wearing at a high rate.

In addition, thrust loads acting on the orbiting scroll members 22 A and 22 B can be transmitted to the orbiting shaft 21 in the opposite directions to each other. Thus, these thrust loads can be canceled by each other in the axial direction. Consequently, the orbiting shaft 21 can bear the thrust loads between the orbiting scroll members 22 A and 22 B, and the orbiting scroll members 22 A and 22 B can be positioned with respect to the axial direction. Accordingly, it is possible to stabilize the behavior of the orbiting scroll members 22 A and 22 B.

When a run-out of end face occurs in the orbiting scroll members 22 A and 22 B during the compression operation, the end plates 23 A and 23 B of the orbiting scroll members 22 A and 22 B are brought into sliding contact with the thrust bearings 11 A and 11 B, thereby allowing a part of thrust loads acting on the orbiting scroll members 22 A and 22 B to be borne by the thrust bearings 11 A and 11 B. Thus, the behavior of the orbiting scroll members 22 A and 22 B can be stabilized even more effectively.

In addition, the rotating shaft 20 , which is a hollow shaft member, has a larger wall thickness at a part thereof on a side opposite to a decentration side toward which the common axis of the orbiting scroll members 22 A and 22 B is radially displaced relative to the axis O 1 —O 1 than at a part of the rotating shaft on the decentration side. Therefore, the orbiting motion of the orbiting scroll members 22 A and 22 B can be balanced by the rotating shaft 20 . Consequently, it becomes unnecessary to provide a special mechanism, e.g. a balance weight, on the rotating shaft 20 and hence possible to reduce the number of components and to simplify the structure of the whole apparatus.

In addition, the pressure chambers 28 A and 28 B are provided at the rear of the fixed scroll members 4 A and 4 B, and intermediate pressures in the compression chambers 26 A and 26 B are led into the pressure chambers 28 A and 28 B, respectively. Accordingly, the fixed scroll members 4 A and 4 B can be continuously pressed toward the end plates 23 A and 23 B of the orbiting scroll members 22 A and 22 B. Thus, it is possible to suppress variations in the gaps in the thrust direction between the distal ends of the wrap portions 6 A and 6 B and the surfaces of the associated end plates 23 A and 23 B and hence possible to increase the compression efficiency.

FIG. 7 shows a second embodiment of the present invention. In this embodiment, the same constituent elements as those in the first embodiment are denoted by the same reference numerals, and a description thereof is omitted. The feature of this embodiment resides in that an intercooler 41 is provided outside the casing 1 at a position between the discharge opening 33 A of the fixed scroll member 4 A and the suction opening 32 B of the fixed scroll member 4 B, and the discharge opening 33 A and the intercooler 41 are connected by a connecting pipe 42 A, and further the suction opening 32 B and the intercooler 41 are connected by another connecting pipe 42 B.

The intercooler 41 is, for example, a cooling device having a heat exchanger 43 , a fan 44 , etc. and adapted to cool high-temperature compressed air discharged from the discharge opening 33 A and lead the cooled compressed air to the suction opening 32 B.

In the second embodiment arranged as stated above, the outside air can be successively compressed by two compression mechanisms comprising the fixed scroll members 4 A and 4 B and the orbiting scroll members 22 A and 22 B. Thus, it is possible to improve the compression performance without increasing the number of turns of the wrap portions 6 A, 6 B, 24 A and 24 B and hence possible to provide a compressor having a reduced diameter.

Moreover, in this embodiment, high-temperature compressed air discharged from the discharge opening 33 A of the fixed scroll member 4 A can be led to the suction opening 32 B of the fixed scroll member 4 B in the state of being pre-cooled by the intercooler 41 . Accordingly, the overall compression efficiency of the apparatus can be increased.

FIG. 8 shows a third embodiment of the present invention. The feature of this embodiment resides in that one of the fixed scroll members has no discharge opening, and the end plate of each orbiting scroll members is provided in the center thereof with a communicating bore that communicates with the inside of the orbiting shaft. It should be noted that in the third embodiment the same constituent elements as those in the first embodiment are denoted by the same reference numerals, and a description thereof is omitted.

Reference numerals 51 A and 51 B denote left and right fixed scroll members used in this embodiment, which are provided in the casing 1 . One fixed scroll member 51 A is arranged approximately in the same way as in the case of the fixed scroll member 4 A in the first embodiment. That is, the fixed scroll member 51 A has an approximately disk-shaped end plate 52 A and a spiral wrap portion 53 A provided on the front side of the end plate 52 A. In addition, a fitting cylindrical portion 54 A is provided on the outer peripheral edge of the end plate 52 A. The fixed scroll member 51 A differs from the fixed scroll member 4 A in the first embodiment in that the fixed scroll member 51 A is not provided with the discharge opening 33 A.

The other fixed scroll member 51 B similarly has an end plate 52 B, a wrap portion 53 B and a fitting cylindrical portion 54 B. However, unlike the fixed scroll member 51 A, the fixed scroll member 51 B is provided with a discharge opening 33 B.

Communicating bores 55 A and 55 B are provided in the respective centers of the end plates 23 A and 23 B of the orbiting scroll members 22 A and 22 B. The communicating bores 55 A and 55 B provide communication between the compression chambers 26 A on the orbiting scroll member 22 A and the compression chambers 26 B on the orbiting scroll member 22 B through the inside of the orbiting shaft 21 .

Accordingly, compressed air from the compression chambers 26 A is led to the compression chambers 26 B through the orbiting shaft 21 and discharged from the discharge opening 33 B to the outside, together with compressed air produced in the compression chambers 26 B.

Thus, the third embodiment arranged as described above also provides advantageous effects approximately similar to those of the first embodiment. In particular, the third embodiment makes it unnecessary to provide the fixed scroll member 51 A with the discharge opening 33 A as stated in regard to the first embodiment and also unnecessary to provide a connecting pipe or the like for connection between the discharge opening 33 A and the air tank. Thus, the structure of the whole apparatus can be simplified.

Although in the foregoing embodiments two Oldham's rings are used to prevent rotation of the two orbiting scroll members, it should be noted that the present invention is not necessarily limited to the described arrangement. For example, one of the two Oldham's rings may be omitted. In such a case also, each orbiting scroll member performs an orbiting motion together with the orbiting shaft as one unit. Therefore, the two orbiting scroll members can be simultaneously prevented from rotating by the remaining Oldham's ring.

Although in the foregoing embodiments, the scroll air compressor comprises two compression mechanisms each consisting essentially of a fixed scroll member and an orbiting scroll member, the present invention is not necessarily limited to the described arrangement. For example, one of the two compression mechanisms may be omitted. That is, the scroll air compressor may comprise only one compression mechanism.

Although in the foregoing embodiments the present invention has been described with regard to a scroll air compressor as an example of scroll fluid machines, the present invention is not necessarily limited to the scroll air compressor, but may also be widely applied to other scroll fluid machines, e.g. vacuum pumps, refrigerant compressors, etc.

As has been detailed above, according to one aspect of the present invention, a fixed scroll member and an electric motor are disposed in a casing on the axis of the casing at a distance from each other. An eccentric bearing having an outer ring, an intermediate ring and an inner ring is provided between the electric motor and the fixed scroll member. The intermediate ring is rotated by rotating a rotating shaft that is integral with the electric motor. The rotation of the intermediate ring causes an orbiting shaft, which is integral with the inner ring, to perform an orbiting motion, thereby causing an orbiting scroll member to orbit. Therefore, it is possible to eliminate the need to additionally provide a crank shaft on the orbiting shaft as stated in regard to the prior art in order to cause the orbiting scroll member to orbit. Thus, the whole apparatus can be reduced in size in the axial direction and formed in a compact structure.

According to another aspect of the present invention, two fixed scroll members are provided in a casing on the axis of the casing away from each other with an electric motor interposed therebetween. Two eccentric bearings each having an outer ring, an intermediate ring and an inner ring are provided between the electric motor and the two fixed scroll members, respectively. The intermediate rings are rotated by rotating a rotating shaft that is integral with the electric motor. The rotation of the intermediate rings causes an orbiting shaft, which is integral with the inner rings, to perform an orbiting motion, thereby causing two orbiting scroll members to orbit. Therefore, it is possible to eliminate the need to provide a crank shaft on the orbiting shaft to cause the orbiting scroll members to orbit. Thus, the whole apparatus can be reduced in size in the axial direction and formed in a compact structure.

Moreover, during the compression operation, a thrust load acting on one orbiting scroll member and a thrust load acting on the other orbiting scroll member can be transmitted to the orbiting shaft in the opposite directions to each other. Thus, these thrust loads can be canceled by each other in the axial direction. Consequently, the thrust loads can be borne between the orbiting shaft and the orbiting scroll members, and the behavior of the orbiting scroll members can be stabilized.

In the present invention, two thrust bearings may be provided at the inner peripheral side of the casing to bear thrust loads acting on the orbiting scroll members, and the orbiting shaft may have a length set so that the rear side of each orbiting scroll member and the front side of the associated thrust bearing are in contact with each other or have a slight gap therebetween. With this arrangement, thrust loads acting on the orbiting scroll members can be canceled by each other in the axial direction. In addition, the thrust loads can be borne by the orbiting shaft, and thus the behavior of the orbiting scroll members can be stabilized.

Even when a run-out of end face occurs in the orbiting scroll members during the compression operation, the end plates of the orbiting scroll members are brought into sliding contact with the thrust bearings, thereby allowing a part of thrust loads acting on the orbiting scroll members to be borne by the thrust bearings. Thus, the behavior of the orbiting scroll members can be stabilized.

In the present invention, the rotating shaft may have a larger wall thickness at a part thereof on a side opposite to a decentering side toward which the orbiting scroll members are decentered than at a part of the rotating shaft on the decentering side. With this arrangement, the orbiting motion of the orbiting scroll members can be balanced by the rotating shaft. Consequently, it becomes unnecessary to provide a special mechanism, e.g. a balance weight, on the rotating shaft and hence possible to reduce the number of components and to simplify the structure of the whole apparatus.

In the present invention, each of the orbiting scroll members may have a communicating bore formed in the center of its end plate so that the communicating bore communicates with the inside of the orbiting shaft. With this arrangement, one of the fixed scroll members need not be provided with a discharge opening and a connecting pipe or the like to be connected to this discharge opening. Thus, the structure of the whole apparatus can be simplified.

In the present invention, the scroll fluid machine may be arranged such that a disc harge opening provided for one of the fixed scroll members is connected to an intercooler, and a suction opening provided for the other of the fixed scroll members is connected to the intercooler. With this arrangement, the outside air can be successively compressed by two compression mechanisms each comprising a fixed scroll member and an orbiting scroll member. Thus, it is possible to improve the compression performance without increasing the number of turns of the wrap portions and hence possible to provide a compressor having a reduced diameter. In addition, high-temperature compressed air discharged from the discharge opening for the one fixed scroll member can be led to the suction opening for the other fixed scroll member in the state of being pre-cooled by the intercooler. Accordingly, the overall compression efficiency of the apparatus can be increased.

Claims

1. 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.

2. A scroll fluid machine according to claim 1, wherein said rotating shaft has a larger wall thickness at a part thereof on a side opposite to a decentering side toward which said orbiting scroll member is decentered than at a part of said rotating shaft on said decentering side.

3. A scroll fluid machine according to claim 1, wherein each of said orbiting scroll members has a communicating bore formed in a center of the end plate, said communicating bore communicating with an inside of said orbiting shaft.

4. A scroll fluid machine according to claim 1, further comprising:suction openings provided in said casing at respective positions facing outer peripheries of the wrap portions of said fixed scroll members; discharge openings provided in said casing at respective positions facing centers of the wrap portions of said fixed scroll members; and an intercooler provided outside said casing; wherein the discharge opening provided for one of said fixed scroll members is connected to said intercooler, and the suction opening provided for the other of said fixed scroll members is connected to said intercooler.

5. A scroll fluid machine according to claim 1, wherein said orbiting shaft extends through said inner rings and said orbiting scroll members are fixedly connected to said orbiting shaft.

6. A scroll fluid machine according to claim 5, wherein said rotating shaft has a larger wall thickness at a part thereof on a side opposite to a decentering side toward which said orbiting scroll member is decentered than at a part of said rotating shaft on said decentering side.

7. A scroll fluid machine according to claim 5, wherein each of said orbiting scroll members has a communicating bore formed in a center of the end plate, said communicating bore communicating with an inside of said orbiting shaft.

8. A scroll fluid machine according to claim 5, further comprising:suction openings provided in said casing at respective positions facing outer peripheries of the wrap portions of said fixed scroll members; discharge openings provided in said casing at respective positions facing centers of the wrap portions of said fixed scroll members; and an intercooler provided outside said casing; wherein the discharge opening provided for one of said fixed scroll member is connected to said intercooler, and the suction opening provided for the other of said fixed scroll members is connected to said intercooler.

9. A scroll fluid machine according to claim 5, further comprising two thrust bearings provided on an inner peripheral side of said casing at rear sides of said two orbiting scroll members, respectively, to bear thrust loads acting on said orbiting scroll members,wherein said orbiting shaft has a length set so that the rear side of each of said orbiting scroll members and a front side of the thrust bearing associated with the orbiting scroll member are in contact with each other or have a slight gap therebetween.

10. A scroll fluid machine according to claim 9, wherein said rotating shaft has a larger wall thickness at a part thereof on a side opposite to a decentering side toward which said orbiting scroll member is decentered than at a part of said rotating shaft on said decentering side.

11. A scroll fluid machine according to claim 9, wherein each of said orbiting scroll members has a communicating bore formed in a center of the end plate, said communicating bore communicating with an inside of said orbiting shaft.

12. A scroll fluid machine according to claim 9, further comprising:suction openings provided in said casing at respective positions facing outer peripheries of the wrap portions of said fixed scroll members; discharge openings provided in said casing at respective positions facing centers of the wrap portions of said fixed scroll members; and an intercooler provided outside said casing; wherein the discharge opening provided for one of said fixed scroll member is connected to said intercooler, and the suction opening provided for the other of said fixed scroll members is connected to said intercooler.