Scroll compressor with variable displacement mechanism

Abstract: In a scroll type compressor wherein a fixed scroll (8) has an end plate (8b) and an involute vane (8a) fixed to the end plate and is coupled to a movable scroll (5) so as to define a pair of working spaces therebetween, the end plate of the fixed scroll are formed a pair of cylinders each of which communicates with the working spaces via bypass holes (15a) and (15b) formed in the end plate of the fixed scroll. In each of the cylinders, a cylindrical piston valve member (10) is slidably received for opening and closing the bypass holes. Opening or closing of each bypass hole is determined depending on a position of an axial end of the piston valve member relative to the corresponding bypass hole.

Description: Background of the Invention: The present invention relates to a variable displacement scroll type compressor to be used, for example, as a refrigerant compressor for an automobile air conditioner and, in particular, to a variable displacement mechanism of a scroll type compressor. Variable displacement mechanisms of scroll type compressors are disclosed in, for example, Japanese First (unexamined) Utility Model Publication No. 1-162094, having a disclosure similar to the EP 0 354 867 A, forming the preamble of claim 1, and Japanese First (unexamined) Patent Publication No. 5-280476, having a disclosure similar to the US 5 451 146. In the former publication, a pair of cylinders each communicating with bypass holes are provided in an end plate of a fixed scroll, and a hollow valve member is slidably received in each of the cylinders for opening and closing the bypass holes. Opening of the innermost bypass hole is achieved by moving the valve member to a position where a hole formed at an intermediate portion of the valve member coincides with the innermost bypass hole. When the innermost bypass hole is opened, refrigerant gas is relieved to the suction side through the innermost bypass hole, the valve member hole and the hollow inside of the valve member. On the other hand, in the latter publication, one cylinder communicating with bypass holes is provided in an end plate of a fixed scroll, and a valve member is slidably received in the cylinder for opening and closing the bypass holes. Opening of the innermost bypass hole is achieved by moving the valve member to an innermost position in the cylinder so as to pass the innermost bypass hole. In the former publication, a diameter of the cylinder is required to be the sum of a diameter of the hollow inside of the valve member and thicknesses of the walls of the valve member. Further, it is possible that the valve member rotates in the cylinder so that the coincidence of the innermost bypass hole and the valve member hole is not guaranteed. Considering the rotation of the valve member, an annular groove communicating with the valve member hole may be necessary on the outer circumference of the valve member. Provision of the annular groove increases thicknesses of the walls of the valve member and thus a diameter of the valve member to thereby increase a diameter of the cylinder. Accordingly, the thickness of the end plate of the fixed scroll is increased to further increase the axial length and the weight of the compressor. On the other hand, in the latter publication, only one cylinder is provided for relieving the refrigerant gas via the bypass holes while a pair of crescent-shaped sealed working spaces are formed as pressure chambers. Thus, the flow rate of the refrigerant gas through the cylinder is large to cause a large pressure loss. For lowering the required power during the reduced displacement operation of the compressor, it is necessary to reduce the pressure loss at the cylinder and thus design the cylinder with a larger bore. Accordingly, like the former publication, the thickness of the end plate of the fixed scroll is increased to further increase the axial length and the weight of the compressor. Summary of the Invention: It is therefore an object of the present invention to provide an improved variable displacement scroll type compressor which can be small in axial length and weight with a smaller thickness of an end plate of a fixed scroll. Other objects of this invention will become clear as the description proceeds. According to the present invention, there is provided a scroll type compressor comprising the features of claim 1. Preferred developments of the invention are given in the dependent claims. Brief Description of the Drawings: Fig. 1 is a sectional view of a variable displacement scroll type compressor according to a preferred embodiment of the present invention; and Fig. 2 is a plan view of a fixed scroll of the compressor shown in Fig. 1. Description of the Preferred Embodiment: Referring to Figs. 1 and 2, description will be made as regards a scroll type compressor according to an embodiment of the present invention. In the figures, numeral 1 denotes a drive shaft having a crank portion 1a. Numeral 2 denotes a funnel-shaped front housing rotatably supporting the drive shaft 1 via bearings 3 and 4. Numeral 5 denotes a movable scroll having an involute vane (spiral wall) 5a with substantially about 2.5 turns and a circular end plate 5b which are formed integral with each other. The movable scroll 5 is rotatably coupled to the crank portion 1a of the drive shaft 1 via a needle bearing 6. Further, between the movable scroll 5 and the front housing 2 is provided a so-called rotation preventing mechanism in the form of combination of a plurality of balls 7 and corresponding circular grooves. Numeral 8 denotes a fixed scroll having, like the movable scroll 5, an involute vane (spiral wall) 8a with substantially about 2.5 turns and a circular end plate 8b which are formed integral with each other. The involute vane 8a extends along a principal surface of the circular end plate 8b around a predetermined axis perpendicular to the principal surface. Numeral 9 denotes a cup-shaped casing or rear housing defining therein a suction chamber 16 and having inlet and outlet ports (not shown). The casing 9 is fixed by bolts (not shown) inserted into bolt insertion holes 9a, along with the front housing 2 and the fixed scroll 8. When the drive shaft 1 is rotated, the movable scroll 5 makes an orbital motion with no rotation on its axis. During the orbital motion of the movable scroll 5, the refrigerant gas in the suction chamber 16 is trapped in a plurality of sealed working spaces 14 defined by the involute vanes 8a, 5a of the fixed and movable scrolls 8, 5, and then the working spaces 14 move along the involute vane 8a towards the predetermined axis while reducing their volumes to achieve compression of the trapped refrigerant gas. The drive shaft 1 is referred to as a scroll driving arrangement. The compressor has a variable displacement mechanism which is incorporated in the end plate 8b of the fixed scroll 8 and comprises a pair of piston valve members 10. Each of the piston valve members 10 is solid and cylindrical. The piston valve members 10 are slidably received in corresponding cylinders 13 formed in the end plate 8b of the fixed scroll 8, respectively. Each cylinder 13 communicates with the working spaces 14 via first and second bypass holes 15a and 15b which are formed in the end plate 8b of the fixed scroll 8 to extend between each cylinder 13 and the principal surface of the end plate 8b. Each cylinder 13 opens to the suction chamber 16 at an peripheral surface of the end plate 8b. The description will be proceeded as regards only one of the piston valve members 10. When the piston valve member 10 moves toward the open side of the cylinder 13 from the position shown in Figs. 1 and 2 where the bypass holes 15a and 15b are both opened, the bypass holes 15b and 15a are closed in order by the piston valve member 10. The piston valve member 10 is arranged to be movable toward an innermost side of the cylinder 13 opposite to the open side thereof until one axial end of the piston valve member 10 located at the open side of the cylinder 13 passes the bypass hole 15b. Accordingly, opening or closing of each bypass hole 15a and 15b is determined depending on a position of the foregoing axial end of the piston valve member 10 relative to the corresponding bypass hole 15a or 15b. Numeral 11 denotes a small-diameter cylindrical valve stopper fixed at the open side of the cylinder 13 for regulating a stroke of the piston valve member 10 within the cylinder 13 to a given value. A coil spring 12 is made of a spring member and is disposed between the valve stopper 11 and the piston valve member 10 so as to bias the piston valve member 10 to the innermost side of the cylinder 13, that is, to the position shown in Figs. 1 and 2 where the bypass holes 15a and 15b are both opened. The innermost side of the cylinder 13 is connected to a discharge chamber 19 through a pressure transmitting path 17 and a pressure control mechanism 18 which is inserted in the pressure transmitting path 17. The pressure control mechanism 18 is for controlling pressure of the innermost side of the cylinder 13 in response to pressure of the suction chamber 16 in the manner known in the art. The pressure of the innermost side of the cylinder 13 urges the piston valve member 10 towards a predetermined direction in the cylinder. On the other hand, the spring 12 urges the piston valve member 10 against the predetermined direction. A combination of the pressure transmitting path 17 and the pressure control mechanism 18 is referred to as a first urging arrangement. The spring 12 is referred to as a second urging arrangement. In the variable displacement scroll type compressor thus structured, the compression is not effected while the piston valve member 10 is located at the innermost side of the cylinder 13, that is, at the position where the bypass holes 15a and 15b are both opened. On the other hand, by moving the piston valve member 10 toward the open side of the cylinder 13 to close the bypass holes 15b and 15a in order, the number of the working spaces increases in sequence to increase the capacity of the compressor. In this event, the second bypass hole 15b may be referred to as an addition bypass hole having a size which is smaller than that of each of the first bypass holes 15a. In the foregoing preferred embodiment, the cylinders 13 forming the variable displacement mechanism are formed in the end plate 8b of the fixed scroll 8 so as to lessen the axial length of the compressor. However, the present invention is not limited to such a structure, but also applicable to a structure where separately prepared cylinders are fixed to the surface of the end plate 8b. As described above, since opening or closing of each of the bypass holes 15a or 15b is determined depending on a position of the axial end of the piston valve member 10 relative to the corresponding bypass hole, it is not necessary to form the piston valve member 10 to be hollow. Further, since the cylinders 13 are provided in pair, the pressure loss can be reduced even if the diameter of each cylinder 13 is small. Accordingly, the diameter of each piston valve member 10 and thus the diameter of each cylinder 13 can be reduced. This can reduce the thickness of the end plate 8b of the fixed scroll 8 so as to provide the compressor with the reduced axial length, size and weight. Further, by forming the piston valve member 10 to be solid and cylindrical, the piston valve member 10 can be easily processed to achieve lowering of the processing cost. While the present invention has thus far been described in connection with a single embodiment thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manner. For example, the end plate of the fixed scroll is formed with three or more bypass holes.

Claims: A scroll type compressor comprising: a fixed scroll (8) having a first end plate (8b) and a first involute vane (8a) extending along a principal surface of said end plate (8b) around a predetermined axis perpendicular to said principal surface, said first end plate (8b) being formed with a pair of cylinders (13) extending parallel to said principal surface at both sides of said predetermined axis, respectively, and with a pair of first bypass holes (15a) communicating said cylinders (13) with said principal surface, each of said cylinders (13) being communicated with a suction chamber (16); a pair of valve members (10) slidably received in said cylinders (13), respectively, each of said valve members (10) determining opening or closing of the corresponding first bypass hole (15a) depending on a relative position between one end of each of said valve members (10) and the corresponding first bypass hole (15a); a movable scroll (5) having a second end plate (5b) and a second involute vane (5a), engaging with said fixed scroll (8) for defining a pair of working spaces (14) in cooperation with said principal surface, said working spaces (14) being placed at both sides of said predetermined axis, respectively, being introduced with fluid from said suction chamber (16), and communicating with said first bypass holes (15a); scroll driving means (1) connected to said movable scroll (5) for driving said movable scroll (5) to reduce each of said working spaces (14) with movement of said working spaces (14) along said involute vane (8a) towards said predetermined axis; and valve displacing means (12, 17, 18) operatively connected to said valve members (10) for displacing said valve members (10) in said cylinders (13); wherein said valve displacing means (12, 17, 18) comprises: first urging means (17, 18) connected to said suction chamber (16) and each of said valve members (10) for urging each of said valve members (10) towards a predetermined direction in each of said cylinders (13); and second urging means (12) connected to said first end plate (86) and each of said valve members (10) for urging each of said valve members (10) against said predetermined direction; characterized in that each of said valve members (10) is a solid body; that said first urging means (17, 18) comprises a pressure transmitting path (17) connected between a discharge chamber (19) and an innermost side of each of said cylinders (13); and that a pressure control mechanism (18) is connected to said pressure transmitting path (17) for controlling said pressure transmitting path (17) in response to the pressure of said suction chamber (16). A scroll type compressor as claimed in claim 1, wherein said second urging means (12) is a coil spring (12) made of a spring member. A scroll type compressor as claimed in claim 1, further comprising a pair of valve stoppers (11) connected to said said first end plate (8b) for restricting said valve members (10) to be moved towards said predetermined direction, respectively. A scroll type compressor as claimed in one of claims 1 to 3, wherein said end first plate (8b) is further formed with a pair of additional second bypass holes (15b) communicating said cylinders (13) with said principal surface, each of said additional second bypass holes (15b) being positioned different from each of the first bypass holes (15a) in said predetermined direction. A scroll type compressor as claimed in claim 4, wherein each of said additional second bypass holes (15b) has a size which is different from that of each of the first bypass holes (15a). A scroll type compressor as claimed in one of claims 1 to 5, wherein each of said valve members (10) is movable toward the other end of the corresponding cylinders (13) opposite to said open end of the corresponding cylinder (13) until one end of the valve member (10) located at said open end of the corresponding cylinder (13) passes said bypass holes (15a, 15b), and opening or closing of each of said bypass holes (15a, 15b) is determined depending on a position of said one end of the corresponding valve member (10) relative to the corresponding bypass hole (15a, 15b).

Inventors: HIGASHIYAMA AKIYOSHI, KAWANO SKIHIRO, SHIMIZU SHIGEMI, TERAUCHI KIYOSHI, HIGASHIYAMA, AKIYOSHI, KAWANO, SKIHIRO, SHIMIZU, SHIGEMI, TERAUCHI, KIYOSHI
Applicants: SANDEN CORP, SANDEN CORPORATION
Application year: 1997
Main classification: F04C29
IPC codes: F04C28, F04B49, F04C18