Method and tool for manufacturing a spiral element for a scroll member used in scroll type fluid displacement apparatus

This invention relates to a scroll type fluid dis-. placement apparatus, and more particularly to a method for manufacturing the spiral element for the scroll and a tool used in the method.

The scroll type fluid displacement apparatus are well known in the prior art. For example, US-A-801,182 discloses a device including two scroll members each having a circular end plate and spiroidal or involute spiral element. The scroll members interfit and are maintained angularly and radially offset from one another so that the spiral elements contact at a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of these scroll members shifts the line contacts along the spiral curved surfaces and, therefore, changes the volume of the fluid pockets. The volume of the fluid pockets increases or decreases depending on the direction of the orbital motion. Therefore, scroll type fluid displacement apparatus is applicable to compress, expand or pump fluids.

Fig. 1 illustrates the basic design of the scroll member suitable for use in a scroll type fluid displacement apparatus such as described in the US-A-801,182 and others. The basic construction of the scroll member 1 comprises a circular end plate 2 and a wrap means or involute spiral element 3 affixed to or extending from one side surface of end plate 2. The scroll type fluid displacement apparatus includes a pair of these scroll members which are maintained at an angular and radial offset so that they interfit and form a plurality of line contacts and axial contact to define at least one pair of sealed off fluid pockets. In this apparatus, each sealed off fluid pocket is defined by the line contacts between interfitting spiral elements and the axial contacts between the axial end surface of the spiral element and the inner end surface of the opposite end plate. The volume of the fluid pocket is thereby defined by both line contacts and axial contacts.

The spiral element is generally formed from a single piece of metal by a machining process, such as milling. However, this process consumes a great deal of time and energy and also produces a large quantity of waste metal. Furthermore, if the spiral element is formed by casting or forging, and an axial dimension of the spiral element is to be made relatively long to obtain a large volume or higher capacity, the draft angle of mould must be made large. After forming in such a mould the amount of machining of a spiral element to obtain uniform wall thickness increased with the result that relatively large quantities of waste metal are produced. Such a manufacturing method also consumes a great deal of time and energy and makes it difficult to obtain a high accuracy of the wall dimension of the spiral element.

It is a primary object of this invention to provide an improvement in a method for manufacturing a spiral element for a scroll member which is used in the scroll type fluid displacement apparatus, such that the production of waste metal during the finishing operation of the scroll member is reduced.

It is a further object of this invention to provide a tool for manufacturing a spiral element which is used in the scroll type fluid displacement apparatus, and which achieves high dimensional accuracy in the machining operation of the spiral element in time efficient manner.

The above object is achieved by a manufacturing method for forming a spiral element for a scroll member used in a scroll type fluid displacement apparatus, which is characterized by the steps of

• (a) preparing a first moulding member having a first involute groove whose sectional configuration is wedge-shaped and a second involute groove whose sectional configuration is substantially rectangular and which is substantially concentric with the first involute groove and separated therefrom by an involute wall, and inserting an involute insertion member with a wedge-shaped sectional configuration into said first involute groove so as to fill said first groove and support said involute wall in a fixed radial position;
• (b) covering said first moulding member with a second moulding member on the side thereof comprising said grooves;
• (c) filling said space formed by said second moulding member and said second involute groove with molten metal and solidifying the metal; and
• (d) removing said insertion member from said first involute groove thus permitting radial flexing of said involute wall and assisting the simultaneous removal of the solidified metal from the second involute groove.

Another aspect of this invention is that the insertion member is removed from the first involute groove with the aid of pushing means. The pushing means comprises pins which are connected to the insertion member and extend axially through holes in the end plate of the first moulding member. The insertion member is, therefore, easily removed from the first involute groove by pushing on the pins.

A manufacturing tool for use in the above inventive method includes

• (a) a first moulding member comprising an end plate and two involute wall elements which are affixed to or extend from one side surface of said end plate to define the two involute grooves, one of said two grooves having a wedge-shaped sectional configuration and the other involute groove having a substantially rectangular sectional configuration and being substantially concentric with said one groove;
• (b) an involute insertion member having a wedge-shaped sectional configuration so as to be removably insertable within said wedge-shaped involute groove; and
• (c) a second moulding member being disposed over said first moulding member to cover said grooves.

During moulding of the metal the rectangular-shaped groove in which the molten metal is disposed cannot expand, therefore, the formed or hardened metal which forms the spiral element of scroll member keeps the rectangular-shaped sectional configuration.

Further objects, features and other aspects of this invention will be understood from the following detailed description of preferred embodiment of this invention referring to the annexed drawings.

• Fig. 1 is a perspective view of the scroll member of a basic design;
• Fig. 2 is an exploded perspective view of the manufacturing tool according to this invention;
• Fig. 3 is a perspective view of the first moulding member used in the manufacturing tool of Fig. 2;
• Fig. 4 is a perspective view of the second moulding member used in the manufacturing tool of Fig. 2;
• Fig. 5 is a sectional view illustrating a portion of the first and second moulding members connected to one another; and
• Fig. 6 is a perspective view of the first moulding member according to another embodiment of the invention.

Referring to Fig. 2, a manufacturing tool 10 for a scroll member in accordance with the present invention is shown. The tool 10 includes a first moulding member 11, an insertion member 12, and a second moulding member 13. First moulding member 11 comprises an end plate portion 111 and two involute wall elements 112 and 113 affixed to or extending from one side surface of end plate 111. The second involute wall element 113 extends along the inner side surface of first involute wall element 112 with a space between them. Two involute grooves 20 and 21 are, therefore, formed between both involute wall elements 112 and 113. The outer side surface of first involute wall element 112 forms vertical surface and the inner side surface forms a tapered surface. The outer side surface of second involute wall element 113 also forms a tapered surface and the inner side surface forms a vertical surface. An outer involute groove 20 is defined by the inner side surface of first involute wall element 112 and the outer side surface of second involute wall element 113, and is thereby wedge-shaped in cross section and, an inner involute groove 21 is defined by the outer side surface of first involute wall element 112 and the inner side surface of second involute wall element 113, and is thus substantially rectangular in cross section. A plurality of holes 114 are formed in end plate portion 111 for connecting between the bottom surface of outer involute groove 20 and opposite side surface of end plate portion 111. Each of holes 114 is placed on the locus of the involute curve which defines the outer groove 20, as shown in Fig. 3. A vent hole 115 is formed on the end surface of end plate portion 111.

Insertion member 12 is disposed in outer groove 20 defined by the inner side surface of first involute wall element 112 and the outer side surface of second involute wall element 113. The sectional configuration of insertion member 12 is substantially the same as that of outer groove 20, i.e., a wedge-shaped configuration. Therefore, the open space of outer groove 20 is filled up by insertion member 12. Insertion member 12 has a plurality of pins 121 axially projecting from one end surface thereof. Each pin 121 is inserted into each hole 114 and outer end portion of pin 121 extends from hole 114.

Second moulding member 13 is disposed over the first moulding member 11 for closing the opening space of both involute grooves 20 and 21. The end surface of second moulding member 13 opposite the first moulding member 11 is formed with a circular indentation 131, as shown in Fig. 4. The indentation 131 provides a moulding space. A pouring gate 22 is formed in second moulding member 13. In this embodiment, as shown in Fig. 2, two pouring gates 22 are formed in second moulding member 13, and a circular sprue runner 221 which is connected to pouring gates 22 is formed in the bottom surface of indentation 131.

In this tool, a supporting member 14 is disposed on the outer side surface of the first involute wall element 112. When the moulding members 11 and 13 are connected by a fastening member, such as bolts and nuts 15 as shown in Fig. 5, the axial end surface of supporting member 14 is fitted against the end surface of second moulding member 13. The predetermined axial distance between the moulding members 11 and 13 is, therefore, maintained by supporting member 14.

The casting method using the above tool will be explained below.

At the first step, first moulding member 11 and insertion member 12 are handled so that insertion member 12 is set in outer involute groove 20. Then, second moulding member 13 is disposed on the first moulding member 11 and is connected to first moulding member 11 by bolts and nuts 15.

At the second step, the molten metal, such as aluminum, is poured into the space defined between the moulding members 11 and 13 through pouring gate 22 and sprue runner 221 formed in second moulding member 13. The space of inner groove 21 and moulding space of indentation 131 are, therefore, filled up by the molten metal. The molten metal is solidified in the subsequent cooling process.

At this time, the expansion of inner groove 21 due to filling up and solidification of molten metal is prevented by insertion member 12 disposed in outer groove 20. Therefore, the sectional configuration of inner groove 21 is not changed, so that the sectional configuration of the spiral element of the formed scroll member has a substantially rectangular cross section. Furthermore, the molten metal which fills up the moulding space of indentation 131 forms the end plate of the scroll member.

In the third step, after solidification of molten metal, the connection between both moulding members 11 and 13 is released and second moulding member 13 is removed from the first moulding member 11. Then, outer end portions of pins 121 of insertion member 12 which extend from holes 114 of the first moulding member 11 are pushed out in the axial direction. Insertion member 12 disposed in outer groove 20 is, therefore, removed from outer groove 20. Because the axial end surface of insertion member 12 is fitted against the end surface of the end plate of the formed scroll member, the formed scroll member is thus removed from inner groove 21 of first moulding member 11 by removing the insertion member 12. The formed scroll member and insertion member 12 are removed from first moulding member 11 at the same time, and therefore, removal of formed scro)) member is smoothly performed. Because the open space of outer groove 20 will be vacated by removal of insertion member 12, involute wall element 112 which separates the outer and inner grooves 20 and 21 can be radially bent, so that the space of the inner groove 21 is made larger.

Fig. 6 shows another embodiment of manufacturing tool according to this invention, in which the involute wall element is modified. The first and second involute wall elements 112 and 113 have a plurality of slits 116 at suitable involute angular positions. Both involute wall elements 112 and 113 are, thus, formed by a plurality of tongue-shaped portions. The removal of the formed scroll member is, therefore, made easier, since, each of the tongue-shaped portions of involute wall element has less rigidity for easier elastic deformation and can be easily bent.

The scroll member formed by the above method and tool is then machined, such as by milling, and thus the final scroll member used in the scroll type apparatus is obtained.

As described above, since the draft angle of the mould of the spiral element portion can be minimized according to this invention, the quantity of waste metal which is produced by finishing of the formed scroll member is reduced. Furthermore, the time and energy for working of the final scroll member is greatly reduced without influence upon the accuracy of the spiral element dimensions.