Scroll type fluid machine

Abstract: Both ends of a circling scroll are supported by a pin crank and the eccentric shaft of the circling scroll, thus assuring a stable circling or oscillating motion of the scroll. This in turn allows the scroll tooth length to be elongated, leading to an increase in the capacity of the fluid machine. Because the eccentric shaft and the pin crank are fitted into the center boss, the pin crank can work as a shaft that supports the left end of the circling scroll. The provision of the boss allows a radial load acting on the scroll tooth to be borne at the load position, thus shortening the shaft and reducing the bearing. Because the pin crank can be mounted to the boss, a two-block parallel arrangement and two-stage arrangement can be implemented easily. Further, the construction in which the pin crank is used as a left-end supporting bearing contributes to reducing the manufacturing cost of the apparatus.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a scroll type fluid machine. Description of the Related Art A conventional scroll type fluid machine generally includes a pair of scroll members of the same shape with a certain thickness, which have clockwise- or counter-clockwise-wound scroll teeth engaged 180 degrees out of phase with each other, with one scroll member fixed and the other performing a circling, but not rotating, motion with respect to the fixed member. A fluid is drawn in between the pair of scroll teeth and its volume is progressively reduced and compressed toward the center of a space formed by the paired scroll teeth. As shown in Figure 3, the scroll tooth is considered as consisting of a plurality of continuous semicircles. If we let R stand for the radius of a smallest semicircle R1 in the upper half of the tooth with respect to the center line, then a smallest semicircle in the lower half has a radius of 2R, a second semicircle R3 in the upper half has a radius of 3R, and a second semicircle R4 in the lower half has a radius of 4R, all these semicircles formed continuous. These scroll teeth are so constructed as to engage with each other from their ends toward their centers during the compression stroke. To allow this motion, bearings that support the scroll members are generally provided outside a scroll disk, and a pin crank mechanism to ensure the circular motion is normally mounted on an outer peripheral portion of the disk. An example of such a conventional scroll tooth construction is described in Japan Patent Publication No. Showa 64-1674. The conventional scroll type fluid machine has the following problems. As to the shape of the scroll teeth, although the scroll teeth are formed in such a way as to allow the fluid compression up to the central portion of the scroll teeth, when we look at the machine as a compressor, it has a relatively large delivery opening at the center for the delivery pressure of 7 kgf/cm2. So, the compressed space mostly comes to communicate with the delivery opening before the compression reaches the central portion. That is, the mechanism of the central portion is not utilized effectively. Denoted 3a in Figure 8 is the delivery opening. Further, because the scroll teeth engage up to the central portion, the bearings supporting the rotation and circling motion are located outside the circling scroll disk in the direction of drive shaft end. This means that the circling scroll disk is supported by the bearing on one side only, degrading the precision of the circling motion. This makes it impossible to elongate the scroll tooth length. Another drawback is that the bearing cannot be mounted at the position where it can efficiently receive a radial load acting on the scroll tooth that is performing the compression stroke. Because the bearing is installed outside the scroll disk, the bearing is applied a moment, which is a product of the radial load acting on the scroll tooth and the distance to the bearing mounting position. So, the bearing must have an excessively large load withstand strength considering the moment. This bearing position also poses a problem of requiring additional space in the direction of axis. Further, to achieve a circling motion without rotating the scroll, a pin crank is commonly employed in recent years. The pin crank is usually mounted on the outer periphery of the scroll disk. Because of its mounted position, the pin crank is not free from instability caused by expansion of the circling scroll disk and the accumulated mounting dimension errors of bearing, disk and housing. One of the steps taken to solve these problems is to install a shock absorbing structure in the pin crank bearing. This structure, however, causes the circling scroll to vibrate during the circling motion. These constructions are shown in Figure 1 and 2. As to the capacity increase, which is one of the major market demands, the problem of accuracy is posed by the elongated scroll tooth length. To deal with this problem, there is a conventional method which forms the circling scroll as a twin type. That is, two circling scroll teeth are formed on both sides of the center mirror disk and two fixed scrolls that engage with the circling scroll teeth are provided on the left and right side. This method can make the scroll teeth length short and therefore solve the precision problem. Because the left and right circling scroll teeth are configured symmetrical with respect to the center mirror disk, however, the imbalance in weight results in a dynamic imbalance during the circling motion. To counter this dynamic imbalance, a large balance weight must be installed. The construction of the conventional twin type is shown in Figure 9, as disclosed in JP Patent Publication N°1-38162. Another conventional machine is shown in US-A-4677949, upon which the preamble of the appended Claim 1 is based. Further, because this correction of dynamic imbalance requires an additional space and cost, it is not possible to increase the eccentricity, a means to effectively increase the delivery capacity, which means that the capacity increase of the twin-type scroll fluid machine is difficult. SUMMARY OF THE INVENTION According to this invention, the circling scroll has a mirror disk installed at the center, on both sides of which are mounted left and right circling scroll teeth in a so-called twin-type configuration, with the left and right teeth set 180 degrees out of phase with each other. In other words, the left and right teeth assumes the same positions if they are turned 180 degrees about the drive shaft axis. More specifically, according to this invention, there is provided a balance type scroll fluid machine according to the appended Claim 1. The circling scroll mirror disk is mounted with a plurality of pin cranks having a bearing at two or more positions along the outer periphery of the mirror disk to prevent the rotation of the circling scroll during the circling motion. The fixed scrolls that engage with the left and right circling scroll teeth are also arranged 180 degrees out of phase with each other. That is, when the left fixed scroll just completes the suction stroke, the right fixed scroll enters the compression stroke, which is 180 degrees apart from the suction stroke. As mentioned above, because the left and right circling scrolls are mounted on both sides of the center mirror disk with the right circling scroll located at a position rotated 180 degrees from the left circling scroll, the halves of the circling scroll divided by a line passing through the drive shaft axis G, as shown in Figure 7, perfectly balance each other in weight. It is noted, however, that the weight correction associated with the bearing 59 must be done by forming drill holes in the boss. As the circling scroll can be formed to be perfectly balanced, there is no need to install a balance weight. Further, in this configuration if the amount of eccentricity is increased, only the mirror disk needs to be enlarged and the halves of the scroll remains balanced in terms of weight, so that the delivery capacity can easily be increased by increasing the eccentricity without a fear of increasing vibrations. Further, because the compression is performed on one side, left or right scroll, at a time, the pulsation during compression stroke decreases to one-half the magnitude of the conventional one. As shown in Figure 8, if a sealing portion is formed on both sides of the mirror disk and along the outer periphery of the disk, this configuration produces the same effect as the two-block parallel arrangement of the scroll compression section. This configuration has the advantage that because the two parallel blocks alternate in performing a series of operations--suction, compression and delivery--the compression strokes on both sides are completely isolated from each other, so that two-way parallel works can be performed simultaneously, for instance, with the right block working as a compressor and the left block as a vacuum pump. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a vertical cross section showing a conventional scroll type fluid machine at the pin crank position; Figure 2 is a cross section showing the conventional scroll teeth engaged with each other; Figure 3 is a schematic diagram showing the conventional scroll tooth; Figure 4 is a vertical cross section of an embodiment of this invention; Figure 5 is a schematic diagram showing a lap construction of the left scroll tooth in a twin scroll type fluid machine of this invention; Figure 6 is a schematic diagram showing a lap construction of the right scroll tooth in a twin scroll type fluid machine of this invention; Figure 7 is a schematic diagram showing a circling scroll construction as an embodiment of this invention; Figure 8 is a vertical cross section of a composite type scroll type fluid machine as an embodiment of this invention; and Figure 9 is a schematic cross section showing the construction of a conventional twin type scroll. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Further embodiments of this invention are described by referring to Figure 4 to 8. Reference numeral 51 represents a left frame which accommodates bearings that support a subshaft 55a. The subshaft 55a is aligned with a drive shaft 55 and receives a drive eccentric shaft 55b. Designated 52 is a right frame which accommodates bearings 57, 58 to support the drive shaft 55. Denoted 53 is a mirror disk of a circling scroll having scroll teeth 53a, 53b on both sides. The scroll teeth 53a, 53b are positioned 180 degrees out of phase about the drive shaft 55 to achieve a weight balance between them. Figure 7 shows the position of the scroll tooth of the circling scroll. Denoted 54 is a key that securely and accurately fixes the engagement between the drive eccentric shaft 55b and the subshaft 55a. A delivery port 56 is provided to each of the left and right scroll teeth. Bearings 59 for the circling scroll are mounted rotatable. A plurality of pin cranks 60 are provided along the outer circumference of the circling scroll to prevent rotation of the scroll. The pin cranks 60 are off-centered by the same eccentricity as the drive eccentric shaft 55b. Denoted 61 is an intake port and 62 a delivery port. Symbol 51a signifies a fixed scroll tooth provided to the left frame, and 52b a fixed scroll tooth provided to the right frame. The construction of balance type scroll teeth of this invention will be described by referring to Figure 5, 6 and 7. Figure 5 shows a cross section of the scroll teeth lap configuration taken along the line 12-12 of Figure 4. Figure 6 shows a cross section of the scroll teeth lap configuration taken along the line 11-11 of Figure 4. Figure 7 shows the circling scroll as seen from the direction of the drive shaft 55, with X-X' representing the drive shaft axis and G representing the center. Now, the engagement of the scroll teeth is explained. Figure 5 shows the engagement between the fixed scroll of the left frame and the left tooth of the circling scroll, with the center of the drive eccentric shaft 55b located at the center G1 that is off-centered by the eccentricity K from the drive shaft axis X-X'. G represents the center of the circling scroll, which has a boss with a radius of R1. The configuration of this scroll teeth conforms to that of the scroll type fluid machine of Japan Patent Application No. Heisei 6-169906, filed on June 17, 1994. The fixed scroll of the left frame that engages with the left tooth of the circling scroll has its center G2 downwardly off-centered by the same eccentricity K from the drive shaft axis and is defined by an arc having a radius R1a about the center G2. They engage as shown in Figure 5. The following relation holds: R1a=R1+K+t. Figure 6 shows the engagement between the fixed scroll of the right frame and the right tooth of the circling scroll, with the center of the drive eccentric shaft 55b located at the center G1 that is off-centered upwardly by the eccentricity K from the drive shaft axis X-X'. G represents the center of the circling scroll. The boss of the right tooth with a radius of R1, unlike the left tooth of the circling scroll of Figure 5, is directed upwardly, that is, formed in the opposite direction to that of the left tooth, as shown in Figure 6. The fixed scroll of the right frame that engages with the right tooth of the circling scroll has its center G2 off-centered in a direction opposite to that of the fixed scroll of the left frame by the same eccentricity K from the drive shaft axis and is defined by an arc having a radius Rla about the center G2. It is noted that the fixed scroll of the right frame is formed in the upward direction and engages as shown in Figure 6. The following relation holds: R1a=R1+K+t. Figure 7 shows the configuration of the circling scroll 53 as seen from the direction of the drive shaft 55, with the solid line 53b representing the right scroll tooth and the dashed line 53a representing the left scroll tooth. When the circling scroll 53 is divided by an arbitrary line passing through the center G, the divided halves completely balance each other in weight. Next, as shown in Figure 8, seals 63 are provided on both sides of the mirror disk of the circling scroll along the outer circumference at the contacting positions in order to form a two-way compression mechanism with suction ports 61a, 61b. This construction allows each scroll tooth to be used for different purposes. For example, one scroll tooth may be used as a compressor while the other is used as a vacuum pump. As shown in Figure 4 to 7, the circling scroll 53 has a left scroll tooth and a right scroll tooth separated from each other by the mirror disk and arranged 180 degrees out of phase. In the state of engagement in which the left scroll tooth has completely drawn in a fluid, as shown in Figure 5, the right scroll tooth of Figure 6 is leading the left scroll tooth by 180 degrees in the compression stroke and the space F of Figure 6 is in the delivery stroke. At this moment, the space F1 of Figure 5 is in the compression stroke. The conventional twin type has the left and right scroll teeth operate in the same strokes so that the spaces F both enter the delivery stroke at the same time. With the construction of this invention, however, the left and right scroll teeth alternately enter the suction stroke or delivery stroke, reducing the pulsation to half. The advantages of these embodiments may be summarized as follows. (1) The circling scroll is formed as a twin type, in which left and right scroll teeth balance each other, so that there is no need to provide a balance weight, ensuring low vibration and high revolution. (2) Because a complete balance is established between the left and right circling scroll teeth in the balance type twin scroll, it is possible to have a large eccentricity and therefore allow the manufacture of a scroll fluid machine of large capacity. (3) A two-way compression mechanism can be formed, which consists of left and right circling scrolls on both sides of the center mirror disk of the circling scroll. It is therefore possible to use the single machine for different purposes, i.e., as a compressor and a vacuum pump. (4) The twin type circling scroll has two circling scroll teeth arranged 180 degrees out of phase with each other. This arrangement reduces the suction and delivery pulsations to one-half the magnitude of the conventional twin type.

Claims: A balance type scroll fluid machine comprising: a central mirror disk (53) of a circling scroll having scroll teeth (53a, 53b) on both sides, said scroll teeth having the same configuration; and fixed scrolls on both sides of said mirror disk (53), having scroll teeth (51a, 52b) respectively engaged with corresponding scroll teeth (53a, 53b) on said mirror disk, CHARACTERIZED in that: said scroll teeth (53a, 53b) of the circling scroll each has a boss at a central portion thereof and are positioned 180 degrees out of phase about a drive shaft axis (X-X') to achieve a weight balance therebetween, and that: one of said scroll teeth (51a, 52b) of the fixed scrolls has a central arc directed upwardly relative to a center point thereof (G2) which is downwardly off-centered from said drive shaft axis (X-X') by the same eccentricity as an eccentric drive shaft (55b) of said mirror disk (53), the other of said scroll teeth (51a, 52b) of the fixed scrolls has a central arc directed downwardly relative to said point (G2), whereby scroll laps on both sides of said mirror disk alternately perform compression operations by 180 degrees. A balance type scroll fluid machine according to claim 1, further comprising seals (63) between said central mirror disk (53) and frames (51, 52) on both sides of said mirror disk along a circumference of said mirror disk to provide a two-way compression mechanism in which scroll laps on both sides of said mirror disk each has a suction and a delivery port (61a, 61b; 62a, 62b).

Inventors: NAKAMURA MITSUO, NAKAMURA, MITSUO
Applicants: ASUKA JAPAN CO LTD, ASUKA JAPAN CO., LTD.
Application year: 1995
Main classification: F04C18
IPC codes: F04C18, F04C23