Scroll Manufacturing Tool

This invention relates to a scroll type fluid displacement apparatus and more particularly, to a tool for manufacturing the scroll.

Scroll type fluid displacement apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 discloses a device including two scrolls, each having a circular end plate and a spiroidal or involute spiral element. These scrolls are maintained at an angular and radial offset so that both spiral elements interfit to make 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 the scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pocket changes. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, scroll type fluid displacement apparatus are applicable to compress, expand or pump fluids.

FIG. 1 illustrates a basic design of a scroll 1 suitable for use in a scroll type fluid displacement apparatus. Scroll 1 includes a circular end plate 2 and a warp or involute spiral element 3 affixed to or extending from one side surface of end plate 2. A scroll type fluid displacement apparatus includes a pair of such scrolls, both of which are maintained at an angular and radial offset so that they interfit and form a plurality of line or radial contacts and axial contact to define at least one pair of sealed off fluid pockets. In such 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 each spiral element and the inner end surface of the end plate of the other scroll. The volume of such pockets is thereby defined by both line contacts and axial contacts.

The scroll is generally formed from a single piece of metal by a machining process, such as milling. However, a milling process consumes a great deal of time and energy and, also produces large quantities of waste metal. If the scroll member is formed by casting or forging, and axial dimension of the spiral element is to be made relatively long to obtain a large volume or higher capacity, the draft angle of mold must be made large. After forming in such a mold, the amount of machining of the spiral element which is necessary to obtain uniform wall thickness is relatively large 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 attain high accuracy of the wall dimensions of the spiral element.

In order to avoid these disadvantages in single piece construction of a scroll, U.S. Pat. No. 3,994,635 (McCullough) discloses a scroll consisting of two pieces. The scroll is formed of a separate end plate and spiral element. The end plate has an involute configured groove in the one side surface and the separate spiral element is seated in the groove. However, in this construction, the process of sealing the spiral element into the groove is intricate. Also, after seating the spiral element, finishing on the surface of end plate and spiral element is intricate and difficult. Furthermore, in comparison with single piece scroll, the reliability of a two piece scroll is inferior.

It is a primary object of this invention to provide an improvement in a manufacturing tool for finishing a preformed single piece scroll which is to be used in a scroll type fluid displacement apparatus.

It is another object of this invention to provide a manufacturing tool which can use a simple finishing process in finishing a preformed single piece scroll.

A manufacturing tool for finishing a preformed scroll for use in a scroll type fluid displacement apparatus according to this invention includes a working member with a first involute element, a separate second involute element and a rotatable member. The working member has an end plate, the first involute element and, a drive shaft. The first involute element extends from one side surface of the end plate and has a cutting edge extending along the inner side wall of its axial end portion. The drive shaft extends from the other end surface of the end plate to effect rotation of the working member. A plurality of arc shaped holes are formed in the end plate along the inner side wall of the first involute element. Outer and inner side walls of the arc shaped hole consist of arcs, the centers of which are concentric with the center of the first involute element. The second involute element has a plurality of pins extending from one of its axial end surfaces and a cutting edge extending along the outer side wall of the other axial end portion. The pins extending from the second involute element extend into the arc shaped holes in the end plate of the working member so that the second involute element interfits with the first involute element with a radial gap. The rotatable member has a plurality of holes into which the axial end portions of the pins fit and a tubular shaft for rotatably supporting the drive shaft of the working member. The drive shaft and/or the tubular shaft are connected to a rotation power source to effect rotation. The radial gap between the inner side wall of the first involute element, which has the cutting edge along its axial end portion, and the outer side wall of the second involute element, which has the cutting edge along its axial end portion, defines the working space for finishing the spiral element of scroll. By using this tool, both side walls of the spiral elements are finished at the same time. Also, the desired thickness of the spiral element can be changed or selected by the rotation of at least one of involute elements.

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

FIG. 1 is a perspective view of a scroll for use in a scroll type fluid displacement apparatus;

FIG. 2 is a diagram illustrating properties of an involute of a circle;

FIG. 3 is a diagram of two involutes illustrating basic properties of an involute wrap of a scroll;

FIG. 4 is a diagram illustrating another property of an involute of a circle;

FIG. 5 is an exploded perspective view of a manufacturing tool according to the present invention;

FIG. 6 is an exploded perspective view of the manufacturing tool as seen from the opposite side of FIG. 5;

FIG. 7 is a perspective view of the manufacturing tool in FIG. 5 in an assembled condition; and

FIG. 8 is a sectional view of the assembled manufacturing tool.

Before the preferred embodiment of this invention is described, principle properties of involute contours, which are used to form spiral elements for scroll type fluid displacement apparatus, will be described with reference to FIGS. 2-4.

Generally, a side wall of the spiral element follows an involute of a circle. FIG. 2 shows such an involute of a circle. This involute is formed by beginning at a starting point P on the generating circle and tracing the involute from the end of an inextensible string unwinding from point P. The curvature of the involute, i.e., the length .rho. along a tangent from the generating circle to the intersection of the involute surface, is given by .rho.=.phi..multidot.rg, where .phi. is the involute angle and rg is a radius of the generating circle. FIG. 3 illustrates two involutes, one involute I starts at point P.sub.1 on the generating circle, and the other involute II starts at point P.sub.2 on the generating circle. Point P.sub.2 is located at an angular offset of .beta. from point P.sub.1. Since, length L.sub.1 along the tangent from the generating circle to the intersection of involute I surface is given by L.sub.1 =.phi..multidot.rg and length L.sub.2 along the tangent from the generating circle to the intersection of involute II surface is given by L.sub.2 =(.phi.-.beta.).multidot.rg, the distance d between the both involutes I and II is given by d=L.sub.1 -L.sub.2 =.phi..multidot.rg-(.phi.-.beta.).multidot.rg=.beta..multidot.rg. Thus, the distance between involutes I and II is uniform and is not influenced by the involute angle at which the distance is measured.

FIG. 4 illustrates another property of an involute of a circle. A line L is drawn tangent to the generating circle and intersects the involute surface at a plurality of points. The distance between these points of intersection is uniform and defines the pitch P of the involute. The pitch P is thus periodic and defined by P=2.pi..multidot.rg.

Referring to FIGS. 5, 6, 7 and 8, a manufacturing tool 10 to form a scroll in accordance with the present invention is shown. Tool 10 includes a working member 11 having a first involute element 112, a second involute element 12 having a plurality of pins 121 projecting from one of its axial end surfaces and, a rotatable member 13.

Working member 11 includes an end plate 111, a first involute element 112 affixed to or extending from one end surface of end plate 111, and a drive shaft 113 extending from the other opposite end surface of end plate 111. An inner side wall of distal axial end portion of first involute element 112 has a cutting edge. The cutting edge is preferably in the form of a tooth 115 which projects inward from the inner side wall of involute element 112 and extends along the entire length of the involute. Tooth 115 is used to finish one side of the spiral element of a preformed scroll. A plurality of arc shaped holes 114 are formed through the end plate 111 along the outer side wall of the first involute element 112. The outer and inner side walls of each arc shaped hole 114 consist of an arc shaped curve, the center of which are concentric with the center of first involute element 112.

Second involute element 12 is rotatably coupled to working member 13 by pins 121 which extend through holes 114. An outer side wall of an axial end portion of second involute element 12 has a cutting edge. The cutting edge is preferably in the form of a tooth 122 which projects outward from the outer side wall of involute element 12 and extends along the entire length of the involute. Tooth 122 is used to finish the other side of the spiral element of a preformed scroll.

Rotatable member 13 includes a circular plate 131. A plurality of holes 132 extend into one end surface of plate 131 and a tubular shaft 133 extends from the other end surface. The axial end portions of pins 121 which extend through holes 114 of end plate 111 are received in holes 132 of circular plate 131. Tubular shaft 133 has a penetrating hole at its center for rotatably supporting drive shaft 113 of working member 11. The center of tubular shaft 133 is concentric with the center of drive shaft 113 of working member 11.

In this tool, the curve of second involute element 12 is formed in the same direction as the first involute element 112 and both involute elements 112 and 12 interfit with a radial gap defined between the facing side walls of the involute elements. Each pin 121 of second involute element 12 extends through a hole 114 of end plate 111 in such a manner as to be movable along the arc shaped direction of the hole. An axial end portion of each pin 121 which extends beyond hole 114 fits into a hole 132 of rotatable member 13. Therefore, second involute element 12 can be moved relative to first involute element 112 by the rotation of rotatable member 13 because pins 121 can move along the arc shaped direction of holes 114. However, the scope of rotation angle of second involute element 12, i.e., the amount which involute element 12 can rotate with respect to involute element 112, is limited by the boundaries of arc shaped hole 114, since pins 121 of second involute element 12 penetrate the boundaries of the arc shaped holes 114. Similarly, while working member 11 can be rotated, the scope of rotation angle of working member 11 is also limited by the boundaries of arc shaped holes 114. Working member 11 and second involute element 12 are thus able to rotate in opposite directions within the scope of a limited angle which is defined by the extent of arc shaped holes 114.

With reference to FIG. 8, a broaching method using the above tool will be explained below.

As a first step, second involute element 12 is placed on working member 11 so that both involute elements 112, 12 interfit with a radial gap. Also, rotatable member 13 is located along the end surface of end plate 111 so that pins 121 of second involute element 12 extend into holes 132 of circular plate 132.

A preformed scroll 14, which has been precision formed as closely to the desired final dimensions and finish as possible, is fixedly disposed on a working table 15. An involute wrap or spiral element 141 of preformed scroll 14 is placed near the gap between tooth 115 on the inner side wall of first involute element 112 and tooth 122 on the outer side wall of second involute element 12.

After this positioning of preformed scroll 14 and tool 10, either working table 15 or tool 10 is axially moved so that tool 10 and scroll 14 move axially toward one another. Alternatively, both table 15 and tool 10 could be moved toward one another. During this motion, both side walls of spiral element 141 of preformed scroll 14 are cut by cutting edges (teeth) 115 and 122. Next, after this first cut, working table 15 or tool 10 is axially moved to separate tool 10 from preformed scroll 14. Thereafter, rotatable member 13 is rotated in a clockwise direction shown as arrow A in FIG. 8). Second involute element 12 is thus rotated through pins 121 by this rotation of rotatable member 13.

This rotation of second involute element 12 reduces the gap between teeth 115, 122. This reduction of the gap can be understood by reference to FIG. 3. As seen therein, if the starting point P.sub.2 of involute surface II is rotated clockwise to be closer to the starting point P.sub.1 of involute surface I, the angle .beta. is reduced and the distance d between surfaces I and II is also reduced.

After this rotation of second involute element 12 with the consequent reduction of the gap between teeth 115, 122, working table 15 and tool 10 are moved axially toward one another again. Both side walls of spiral element 141 are cut an additional amount by teeth 115, 122. In these cutting operations, both side walls of spiral element 141 are finished at the same time. The use of tool 10 also improves the uniformity and the dimensional accuracy of spiral elements finished with the tool. Furthermore, tool 10 can be adjusted to the desired thickness of the spiral element being finished by rotation of the second involute element.

This invention has been described in detail in connection with the preferred embodiment, but these are merely examples only and this invention is not limited thereto. It will be easily understood by those skilled in the art that variations and modifications can be easily made within the scope of this invention.