Asynchronous non-constant-pitch spiral scroll-type fluid displacement machine
A scroll-type spiral fluid displacement machine having at least one pair of interfitting scroll elements. The scroll vanes of the scroll elements are constructed upon a base line spiral defined by the equation: L=K0φK1e−φ/K2 where L is the distance from the spiral's origin to any point on the spiral curve, φ is the angular displacement of the spiral, K0 is a constant greater than 1, K1, is a constant greater than 1, and K2 is a constant greater than 10.
1. Field of the Invention
This application relates generally to a spiral scroll-type fluid displacement machine and more particularly to an asynchronous non-constant pitch spiral scroll-type fluid displacement machine.
2. Description of the Related Art
Generally, a conventional spiral scroll-type fluid displacement machine is formed with a pair of scroll elements (i.e., an orbiting scroll element and a fixed scroll element) each having spiral vanes that are fitted together in a certain predetermined way to intake fluid such as air or water through an intake port. The interfitting spiral vanes create one or more fluid pockets and trap the fluid inside the pocket(s) by moving the orbiting scroll element in a predetermined manner. The fluid pocket moves toward an outlet port while maintaining pressure in the pocket by continuously moving the orbiting scroll element within the interfitted fixed scroll element. The pressurized fluid is discharged though an outlet port.
U.S. Pat. No. 801,182 (Creux) describes a conventional spiral scroll-type machine. A typical spiral scroll-type machine includes a pair of scroll elements where one scroll element is termed a fixed scroll and the other one is termed an orbiting scroll. Either the fixed or orbiting scroll comprises a spiral vane or a curled up wrap connected to an end plate in such a manner that the spiral vane is perpendicular to the planar surface of the end plate. The projecting spiral vanes or wraps of the fixed and orbiting scrolls interfit to form a plurality of line contacts between them, and thus at least one pair of fluid pockets is formed. The fixed scroll is stationary and does not move. The orbiting scroll does not rotate by revolving around its center. Rather the movement of the orbiting scroll is an orbiting motion. That is, the non-rotating orbiting scroll is moved in an orbit (generally circular in shape) formed around the center of the fixed scroll. With such orbiting motion, the line contacts between the spiral vanes of the fixed and orbiting scrolls move along the curved surfaces of spiral wraps, thereby creating fluid pockets and possibly changing the volume of (and thus the pressure in) the fluid pockets. The volume can be increased or decreased depending on the orbiting direction of the orbiting scroll, or the geometry of the spiral vane structure. Therefore, a spiral scroll type machine can compress or expand fluids for pumping action.
In the past decade, the rapid development of the computer and the availability of high-precision CNC machines propelled a marvelous progress in this field. This type of fluid displacement machine demonstrates the following advantages:
1. High efficiency—mainly because the process of suction-compression-discharge occurs continuously and the expansion of remaining fluid into suction pocket does not exist, thereby offering a higher volume efficiency.
2. Torque varies in a relatively small range during a full rotation. Vibration is kept at the low level, as is the noise.
3. The structure is simple and compact.
The scroll-type compressor has gained increasing popularity and taken more and more market share, which used to be occupied by other types of compressors (such as the reciprocating-type compressor and rotary-type compressor, among others), especially for small-size compressors ranging in power from 0.5 to 15 kilowatts. Scroll-type fluid displacement machines are being widely used in some industries such as for air-conditioning and medical equipment. In order to meet the requirements for broader industry applications, it is desired to further optimize the design of these types of machines.
Although this design concept of scroll-type fluid displacement machines appeared as early as the beginning of twentieth century, its development was hindered due the difficulty to optimize its design and the requirement for high precision machining. A lot of effort is now being invested to improve the performance and reliability of scroll-type fluid displacement machines. Some are focusing on developing dual scroll compressors to enlarge capacity and achieve higher energy efficiency (as in U.S. Pat. Nos. 5,258,046 and 5,556,269). Some are emphasizing the axial and/or radial compliant mechanism (as in U.S. Pat. Nos. 4,846,639, 6,461,131, and 6,695,600). Some are focusing on a coating treatment on the spiral surface in order to prevent seizure or friction and provide good lubrication between scroll wraps. Some are trying to provide a better rotation preventive device (as in U.S. Pat. No. 6,752,606). Designing scroll vanes to improve the performance of compressor is one of various key areas. Some are focusing on the central portion of spiral surface (as in U.S. Pat. No. 5,513,967). Some are stressing on finding an appropriate scroll curve to increase the volume ratio (as in U.S. Pat. No. 5,458,471), or minimize the machine size (as in U.S. Pat. No. 5,318,424), or for special requirements (as in U.S. Pat. No. 5,547,353).
However, the conventional scroll-type fluid displacement machines have problems in that the fluid pressure distribution and the fluid pressure variation during operation are not optimized such that the conventional scroll-type fluid displacement machines have the shortcomings less-than-optimal efficiency, and relatively high noise and vibration, all of which contributes to decreased durability of the machines.
SUMMARY OF THE INVENTIONWith the aid of sophisticated computer-based real-time measurement systems and advanced computer fluid dynamics analysis, it was found that fluid pressure distribution and variation during the operation of scroll-type fluid displacement machines is key to the design of a new fluid displacement machine structure, and to choose an appropriate curve for scroll wraps. The present fluid displacement machine overcomes the general shortcomings of current machines and manifest inherent advantages such as high efficiency, low noise, low vibration and enhanced durability. With such consideration and using an optimization technique, the present invention uses a single, continuous curve as the base line for constructing scroll vanes.
The scroll vanes of the present invention are constructed based upon a base line spiral defined by the equation:
L=K0φK1e−φ/
Wherein L is the distance from the origin to any point on the spiral curve, φ is the angular displacement of the spiral, Ko is a constant greater than 1, K1 is a constant greater than 1, and K2 is a constant greater than 10.
The fluid displacement machine according to a preferred embodiment of the present invention comprises two pairs of scroll elements, where each element is made up of a fixed scroll and an orbiting scroll. These two pairs of scroll elements are separate and mounted in a back-to-back manner. The scroll wraps of the two orbiting scrolls are symmetric with respect to the central axis of a driving shaft. So are the scroll vanes of two fixed scrolls. Two pairs of scrolls are offset by a phase difference of 180 degrees. These two orbiting scrolls share the same orbiting circle.
The scroll elements can be mounted on two separate crankshafts, of which the eccentric parts are positioned opposite radially. The two crankshafts are then linked with a rigid coupling such that the rotation force can be transmitted to the second crankshaft through the first one. The fluid displacement machine has two inlets and two outlets. The inflowing fluid will be divided and may be compressed or expanded through either pair of scrolls simultaneously. The discharged fluid from each outlet is then merged together to export.
Referring to
The orbital movement generating mechanism for this preferred embodiment comprises two crankshafts 4 and 10 connected by the rigid coupling 6. However, the orbital movement generating mechanism could comprise a single crankshaft or any other means for producing non-rotating relative orbital movement between the orbital and fixed scrolls. It is noted that, none of the scrolls necessarily needs to be fixed as long as relative orbital movement between mating scrolls is achieved through some means.
As shown in
C3 represents the orbiting circle along which the center of C1 and the center of C2 travel. The orbiting scroll 2 is mounted on eccentric part 4a and the orbiting scroll 9 is mounted on eccentric part 10a, so these two orbiting scrolls share the same orbiting circle. When connecting crankshaft 4 and crankshaft 10, it is preferred that the centers of the eccentric parts 4a and 10a of both crankshafts 4 and 10 are located radially oppositely with respect to the circle C3. Such an arrangement simplifies the balancing of the machine. As shown in
The scroll-type fluid displacement machine in accordance with present invention preferably comprises two inlets and two outlets. Referring back to
The non-constant-pitch spiral curve shown in
L=K0φK1e−φ/
where
L: the distance from the origin to any point on the spiral curve;
φ: the angular displacement of the spiral curve
K0: a real number greater 1, (K0>1)
K1: a real number greater 1, (K1>1)
K2: a real number greater 10, K2>10
The strategy to select an appropriate spiral curve is:
1. To obtain a high volume ratio. The ratio of the displacement (Vs) to the final compression volume (Ve) is required to be high enough to meet the requirement according the application of the scroll-type fluid displacement machine.
2. To use a single, continuous, smoothly changing curve to define the scroll wraps for its entire length. It is required that the change of the volume of the fluid pocket formed between two scrolls be smooth and continuous in order to increase or decrease the fluid pressure smoothly and avoid shock.
3. When the former two conditions are satisfied, it is desired to have a spiral curve, which defines a faster change of volume of the fluid pocket. In so doing, the full cycle of suction-processing-discharge is shortened. Energy efficiency can be also enhanced.
The particular curve shown in
L=2φ1.5e−φ/100
It is important to note that this particular curve is just a member of a family of curves that are described by the equation. In practice, the consideration of performance requirements including power, physical properties of fluid and pressure ratio, will be included in the design of the curve. All these requirements must be met with the highest priority. Then the curve will be optimized to enable the fluid displacement machine to achieve its optimum performance in terms of its fluid dynamics. The result of optimization is the best combination of three parameters: K0, K1 and K2. The intended machine will be improved in the following aspects: increased operating efficiency, reduced vibration, reduced noise and increased durability.
The proposed curve can be used to construct a scroll vane for a single-scroll fluid displacement machine as well as dual-scroll fluid displacement machine. A typical method is employed to construct the scroll vanes for a single-scroll fluid displacement machine.
The proposed curve can be also adopted in the design of dual-scroll fluid displacement machine. A typical dual-scroll fluid displacement machine has a crankshaft which goes through the fixed scroll 22 and the orbiting scroll 20. In order to allow the eccentric part of the crankshaft to pass through the central portion of orbiting scroll 20, the spiral scrolls must start from some angular offset, such as is depicted in
It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While various embodiments including the presently preferred one has been described for purposes of this disclosure, various changes and modifications may be made, which are well within the scope of the present invention. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.
Claims
1. A scroll-type fluid displacement device comprising:
- a first scroll and a second scroll, each scroll having an end plate from which a spiral projects transversely from the end plate;
- said first scroll and said second scroll being opposingly arranged to interfit said spirals;
- said spirals being opposingly symmetrical about a central axis;
- a base line for each spiral be defined by the equation: L=K0φK1e−φ/K2
- wherein L is the distance from said central axis to any point on the base line curve, φ is the angular displacement of the base line curve, Ko is a constant greater than 1, K1 is a constant greater than 1, and K2 is a constant greater than 10.
2. The device according to claim 1 further comprising an orbital movement generating mechanism that moves at least one of the scrolls so that said first scroll moves in a non-rotating orbital path perpendicular to said central axis, relative to said second scroll.
3. The device according to claim 1 further comprising a housing to which one of said scrolls is rigidly affixed.
4. The device according to claim 2 wherein said orbital movement generating mechanism is a rotationally driven crankshaft.
5. The device according to claim 1 further comprising a third scroll and a fourth scroll that are defined and interfit in the same manner as said first and second scrolls;
- wherein said first and third scrolls are rigidly affixed to a housing; and
- wherein said second and fourth scrolls are driven in a non-rotating orbital path perpendicular their respective central axes, relative to said first and third scrolls.
6. The device according to claim 5 wherein the central axes of said second and fourth scrolls are parallel;
- wherein said second and fourth scrolls are driven in the same direction on their respective orbital paths and at an angular phase difference of 180 degrees.
7. The device according to claim 5 wherein said second and fourth scrolls share a common central axis.
8. A method of designing scroll elements for a scroll-type fluid displacement device, the steps comprising: wherein L is the distance from a central axis to any point on the base line curve, φ is the angular displacement of the base line curve, Ko is a constant greater than 1, K1, is a constant greater than 1, and K2 is a constant greater than 10;
- designing a base line spiral for first and second scroll elements, the base line spiral being defined by the equation: L=K0φK1e−φ/K2
- designing inner and outer spirals to define spiral walls that create fluid pockets having a desired change in volume when said first and second scroll elements are fit and orbitally rotated together in the scroll-type fluid displacement device.
Type: Application
Filed: Jul 16, 2007
Publication Date: Jan 22, 2009
Inventors: Zhihuang DAI (Chicago, IL), Zhengzhi ZHAN (Westmont, IL)
Application Number: 11/778,131
International Classification: F04C 18/063 (20060101);