Patent Publication Number: US-6709250-B1

Title: Gear and a fluid machine with a pair of gears

Description:
FIELD OF THE INVENTION 
     The present invention relates to a gear, more particularly, to the gear which has at least one longer tooth, shorter teeth and transition teeth. 
     In addition, the present invention relates to a fluid machine more particularly, to the fluid machine for conveying, compressing or expanding liquid or gaseous fluids, which has at least one gear pair according to the present invention. 
     PRIOR ART 
     In the prior arts in addition to be widely used as driving force transmission, the gear can also be used in many other fields. For example, a pair of gear-shaped rotors can be used as a gear pump to transport liquid fluids. However, the effective area used for fluid transferring by the rotors of the gear pump is relatively small, so the pumping efficiency is kept low. U.S. Pat. No. 3,574,491 discloses a gear-type rotary machine for transporting liquid fluid and compressing or expanding gaseous fluids, which consists of a housing and two engaging gear-shaped rotors being accommodated in the housing. Each gear includes two sets of shorter teeth alternating with one or more longer teeth. Because the two engaging gear-shaped rotors are provided with longer teeth, the effective area used for fluid transferring by the rotors of the gear pump is greatly increased. Unfortunately, when the longer teeth of the two rotors go to be near the inflection point of the “8”-shaped housing, because the profile of the longer tooth is not perfectly designed, the seal effect cannot be kept between the two longer teeth, resulting in a great amount of liquid backflow, thus the efficiency of the fluid transmission is caused at a low level, with nearly no function of compressing or expanding gas. In fact, although the two rotors keep engaging with each other, they are out of actual metallic contact with each other; additional torque transmitting gears have to be mounted outside so as to drive the shaft of the rotor, so the size of the rotor machine has to be increased. 
     U.S. Pat. No. 5,682,793 discloses an engaging rotor. When it is used for compressing gas, the gas in the tooth groove  3  of the rotor  1  cannot be compressed, only being moved from the inlet to the outlet. When the groove communicates with the compression chamber or the outlet, the gas is compressed at a constant volume, resulting in the power consumption increased and noise generated. When used for compressing gas, it becomes a rotor compressor with partial built-in compressing process. If every rotors are formed with a longer tooth and a longer tooth groove, when the longer teeth go to be near the inflection point of the “8”-shaped housing, the perfect seal effect cannot be realized, so some liquid will backflow and leak to the outside, thus the engaging rotor of this patent is inappropriate to be used in a compressor. 
     On the other hand, in the rotary compressors according to the prior art, the rotor compressors, the sliding-plate compressor, and the rotary vane compressor are all provided with the sliding-plates, the springs, the valves or the like which are easy to be damaged. The screw-rod compressor or the scroll compressor is simple in structure, but their curve surfaces are complex in shape, so it is difficult to be manufactured and checked. More particularly, in condition that those compressors are miniaturized, above-mentioned drawbacks are even worse. For the single tooth rotor compressor, the two rotors are out of actual metallic contact with each other, a clearance is kept between the corresponding engaging points of the two rotors. In such kind of compressor, a great of leakage between the two rotors can not be prevented, and it is difficult to make the compression ratio big enough. In fact, the single-stage compressor can only be used as an air blower. Because the rotors cannot transmit force to each other for their profiles, the angular position and the rotation of one rotor relative to another are controlled by a separate gear which can be synchronously rotated with said one rotor. The synchronous gear and its assembly make the compressor complex in structure and big in volume. 
     OBJECT OF THE INVENTION 
     An object of the present invention is to provide a gear as a component of fluid compressing or expanding machine so as to transport fluid more efficiently. 
     Another object of the present invention is to provide a gear whose inertia force when used as a rotor can be cancelled out completely, although the teeth of which have different sizes with respect to each other. 
     A further object of the present invention is to provide a gear pair for reducing the leakage between the two engaging gears as rotors. 
     An additional object of the present invention is to provide a compressor or expansion machine, which has a complete built-in compression process, so its compression ratio can be obviously enhanced, so that the single-stage compressor can also be used as the compressor for generating pressured gas and the compressor for refrigerator, without over compression and under compression. 
     Another object of the present invention is to provide a fluid machine which have a perfect sealing effect. 
     TECHNICAL SOLUTIONS 
     A gear pair according to the present invention are formed as at least two gear-shaped rotors that engage with each other, so that the driving force can be transmitted. The driving gear and the driven gear are provided with shorter teeth, transition teeth and at least one longer tooth on their pitch circles respectively. The cross-section of the longer tooth is of a hawk beak shape, and the profile of the longer tooth is smoothly connected one after another by a convex section of the longer tooth, a tip section of the longer tooth, a concave section of the longer tooth and a leading section of the longer tooth. A transition tooth is provided on each of the two sides of the longer tooth. Each transition tooth is provided in neighborhood relationship with the longer tooth on one side thereof and a shorter tooth on the opposite side thereof. That is, the teeth of gear according to this invention is distributed in the order of a shorter tooth, a transition tooth, a longer tooth, the other transition tooth, and another shorter teeth. 
     An external engaging gear pair according to the present invention comprises at least two gear-shaped rotors that engage with each other. The two rotors are provided with shorter teeth, transition teeth and at least one longer tooth on their pitch circles respectively. The shaft of the driving rotor and the shaft of the driven rotor are arranged to be parallel to each other. The center to center distance from the driving rotor to the driven rotor is equal to the radial sum of the pitch circles of the two rotors. The cross-section of the longer tooth is of a hawk beak shape, the profile of the longer tooth is composed of a convex section, a tip section, a concave section and a leading section of the longer tooth, which are smoothly connected one to another in series. The longer tooth is connected at its two sides to the shorter teeth via transition teeth. 
     At least one gear pair according to the present invention is formed as two gear-shaped rotors that engage with each other. One of the two rotors is an internal gear, and another is an external one, the two rotors are provided with shorter teeth, transition teeth and at least one longer tooth on their pitch circles respectively. The shaft of the driving rotor and the shaft of the driven rotor are arranged to be parallel to each other. The center to center distance from the driving rotor to the driven rotor is equal to the radial difference of the pitch circles of the two rotors. The cross-section of the longer tooth is of a hawk beak shape, the profile of the longer tooth is composed of a convex section of the longer tooth, a tip section of the longer tooth, a concave section of the longer tooth, and a leading section of the longer tooth. The four sections of the longer tooth are smoothly connected one to another in series, so as to form the profile of the longer tooth. The convex section of the longer tooth of the internal gear projects into the inside of the pitch circle of the internal gear, while the leading section thereof recesses into the outside of the pitch circle. The convex section of the external gear projects into the outside of the pitch circle of the external gear, while the leading section thereof recesses into the inside of the pitch circle. Two transition teeth are respectively provided at the two sides of the longer tooth between the longer tooth. Each transition tooth is in neighborhood relationship with the longer tooth on one side thereof and a shorter tooth on the other side thereof. 
     According to another aspect of the present invention, the external engaging gear-type compressor includes a casing which is composed of an “8”-shaped housing, an tipper end cover and a lower end cover. At least one pair of engaging gear-shaped rotors are accommodated in the casing, and each pair of engaging gear-shaped rotors include one driving rotor and one driven rotor. An gas inlet is provided on the casing, and at least one gas outlets are provided on the end covers. The driving rotor and driven rotor are provided with shorter teeth, transition teeth and at least one longer tooth on their pitch circles respectively. The cross-section of the longer tooth is of a hawk beak shape, and the profile of the longer tooth is composed of a convex section, a tip section, a concave section and a leading section. The four sections are smoothly joined together in a manner of one after another, so as to form the profile of the longer tooth. The two sides of longer tooth are both adjacently provided with a transition tooth which in turn adjoins a shorter tooth. An elementary volume is enclosed by the longer teeth of the rotors, the engaging point, the wall of the housing, the upper end cover, and the lower end cover. When the gear-type compressor operates, the elementary volume varies periodically. When the elementary volume increases, the elementary volume communicates with the gas inlet, while when the elementary volume reduces, the elementary volume communicates with the gas outlet, so as to accomplish a complete working process of a suction, a compression and an evacuation. 
     According to another aspect of the present invention, the internal engaging gear-type compressor includes a casing which comprises a cylinder, an upper end cover, and a lower end cover. A shims in a shape of a part of moon is accommodated in the casing. The shim occupies the superfluous portion of the rotating space of the driving and driven rotors. At least one pair of internal engaging gears which include one driving rotor and one driven rotor are provided within the casing. Gas inlet and gas outlet are provided on the end covers. The driving rotor and the driven rotor are provided with shorter teeth, transition teeth and at least one longer tooth on their pitch circles respectively. The cross-section of the longer tooth is of a hawk beak shape, and the profile of the longer tooth is composed of a convex section, a tip section, a concave section and a leading section. The four sections of the longer tooth are smoothly connected one after another, so as to form the profile of the longer tooth. The convex section of the external gear projects into the outside of the pitch circle of the external gear, while the leading section recesses into the inside of the pitch circle thereof. The convex section of the internal gear projects into the inside of the pitch circle of the internal gear, while the leading section thereof recesses into the outside of the pitch circle. The two sides of the longer tooth are both provided with a transition tooth which adjoins a shorter tooth in turn. An elementary volume is enclosed by the longer teeth of the two rotors, the engaging point, the upper and the lower end covers, and the shim. When the gear-type compressor operates, the elementary volume varies periodically. When the elementary volume increases, the elementary volume communicates with the gas inlet, while when the elementary volume reduces, the compression starts, then the elementary volume communicates with the gas outlet, so as to accomplish a complete working process of a suction, a compression and an evacuation. 
     ADVANTAGES OF THIS INVENTION 
     1. The two rotors keep engaging with each other, so that the driving force is directly transmitted from the driving rotor to the driven rotor while the working medium is perfectly sealed. In this way, the compressor can be simplified in structure, and the components of the compressor can be minimized. 
     2. The two rotors are both provided with the shorter teeth, the transition teeth and the longer teeth. Since the longer tooth is higher than the shorter tooth many times, the space between the rotors and the surrounding housing becomes larger, so that more effective area used for transferring fluid by the rotor of the gear pump can be used to transfer, compress or expand more working medium during one rotating working process of the rotors. As the effective area used for transferring fluid by the rotor of the gear pump is increased, the working efficiency of the gear pump is also improved. 
     3. For the external engaging gear-type compressor, when the tip sections of the longer teeth of the two rotors passes the edge of the gas inlet, an elementary volume is enclosed by the longer teeth of the two rotors, the engaging point, the wall of the “8”-shaped housing, and the upper and the lower end covers. In the compressor, the working medium is compressed so as to have a high-pressure. A clearance between the tip sections of the longer teeth of the two rotors and the housing is used to seal the working medium (the so-called slit seal solution). When the tip section of the longer tooth of the driving rotor reaches to the inflection point of the “8”-shaped housing, the tip section of the longer tooth of the driven rotor also reaches to the inflection point of the “8”-shaped housing. Once the tip sections of the longer teeth of the two rotors begin to disengage with the wall of the “8”-shaped housing, the tip section of the longer tooth of the driving rotor begins to engage with the starting point of the concave section of the longer tooth of the driven rotor. At this time, the tip section of the longer tooth of the driving rotor engages with the concave section of the longer tooth of the driven rotor, so that the working medium is kept being sealed. As no gap is appeared in the engaging point between the two rotors when the longer teeth of the two rotors disengage with the inflection point of the housing, the leakage of the working medium is prevented, so that the sealing effect can be kept during the complete working process. However, when the rotor with the traditional longer tooth profile is used, as the longer tooth of one gear engages with the longer tooth interval of the other gear, a gap is appeared between the high-pressure and low-pressure chambers when the longer teeth leave the inflection point of the “8”-shaped housing, resulting in a large amount of working medium backflow. 
     4. For the internal engaging gear-type compressor, when the tip section of the longer tooth of the driving rotor or the external gear passes the lower tip of the shim in the shape of a part of moon, an elementary volume is enclosed by the longer teeth of the two rotors, the engaging point of the two rotors, the shim in the shape of a part of moon, and the upper and the lower end covers. The working medium is sealed by means of the clearance provided between the longer teeth of the two rotors and the shim in the shape of a part of moon. Once the tip sections of the longer teeth of the driving and driven rotors reach to the upper tip of the shim in the shape of a part of moon, the tip sections of the longer teeth of the two rotors begin to disengage with the upper tip of the shim in the shape of a part of moon simultaneously. At the same time, the tip section of the longer teeth of the driving rotor is in engagement with the starting point of the leading section of the longer teeth of the driven rotor, so that an elementary volume is enclosed by the engaging point between the two rotors, the engaging point between the tip section of the longer tooth of the driving rotor and the concave section of the longer tooth of the driven rotor, and the upper and the lower end covers. In this way, no gap between the two longer teeth is appeared when the longer teeth of the two rotors pass through the upper tip of the shim in the shape of a part of moon, so that the perfect sealing effect is kept during the complete working process of a compression and an evacuation. 
     5. As the two rotors are in actual metallic engagement with each other, the fluid leakage between the two rotors can be minimum. In addition, as an oil injection technique is used, the fluid leakage through the clearance between the tip sections of the longer teeth and the housing and through other leakage passages can be greatly reduced, so that the volumetric efficiency is high and the compression ratio is also high. 
     6. All of the working medium in the closed elementary volume can be evacuated from the gas outlet, so no closed volume at the suction stage and/or closed volume at the discharge stage are remained in the compressor, so that the volumetric efficiency is improved. 
     7. When a rotor is provided with two or more longer teeth, since the longer teeth are symmetrically arranged with respect to the shaft of the rotor, the inertia force can be cancelled out completely. When the rotor is provided with only one longer tooth, the inertia force of the rotor can also be cancelled out completely by means of a balancing weight. As a result, the compressor can always be able to be kept a minimum vibration and noise. 
     8. In the prior art, the slip sheets, the spring and the valves as components of a compressor always subject to forces periodically varied, so they are liable to be damaged for fatigue reasons. In the present invention, however, no easily damaged components, such as the slip sheets, the spring and the valves, are arranged, so that the compressor seldom stop to work for the damage of the easily damaged components, thus the compressor according to the present invention is high in reliability. 
     9. Variant working conditions and variant capacity requirements can be conveniently met by means of regulating a slide valve, so as to help to save energy. 
     10. The rotor may be designed to have teeth which are perpendicular to the side surface of the rotor, so it is easier to manufacture the rotor. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The present invention will be further described together with the accompanying drawings, in which 
     FIG. 1 is a schematic view showing the structure of rotors according to the present invention. 
     FIG. 2 is a schematic view showing one embodiment of the profile of the teeth of the driving rotor of the present invention. 
     FIG. 3 is a schematic view showing one embodiment of the profile of the teeth of the driven rotor according to the present invention. 
     FIG. 4 is a schematic view showing the structure of the external engaging gear-type compressor according to the present invention. 
     FIG. 5 is a schematic view of the whole structure of one embodiment of the present invention, in which the upper end cover is provided with a slide valve regulating means and liquid spraying apertures. 
     FIG. 6 is a schematic view of the whole structure of one embodiment of the present invention, in which the lower end cover is provided with a slide valve regulating means and liquid spraying apertures. 
     FIG. 7 is a schematic view of the whole structure of one embodiment of the present invention, in which the end cover is provided with an gas inlet. 
     FIG. 8 is a schematic view showing one embodiment of the structure of the rotors of the internal gear pair according to the present invention. 
     FIG. 9 is a schematic view showing one embodiment of the profile of the external gear according to the present invention. 
     FIG. 10 is a schematic view showing one embodiment of the profile of the internal gear according to the present invention. 
     FIG. 11 is a schematic view showing one embodiment of the whole structure of the internal engaging gear-type gas compressor according to the present invention. 
     FIG. 12 is a schematic view showing another embodiment of the whole structure of the internal engaging gear-type gas compressor according to the present invention. 
     FIG. 13 is a schematic view of a portion of one embodiment of the present invention illustrating the upper and lower end covers. 
     FIG. 14 is a schematic view of a portion of another embodiment of the present invention illustrating the upper and lower end covers. 
    
    
     BEST EMBODIMENTS FOR CARRYING OUT THIS INVENTION 
     The rotors according to the present invention includes a driving rotor  214  and a driven rotor  224 . The shaft  211  of the driving rotor  214  and the shaft  21  of the driven rotor  224  are arranged to be parallel to each other. The center to center distance from the driving rotor  214  to the driven rotor  224  is equal to the sum of the radii of the pitch circles  212  and  222  of the two rotors. The driving rotor  214  is formed with shorter teeth  210 , convex transition teeth  217 , concave transition teeth  28  and a longer tooth  27 . The cross-sections of the longer teeth  27 ,  219  of the driving and driven rotors  214  and  224  respectively are of a hawk beak shape. The profile of the longer tooth  27  of the driving rotor  214  includes a convex section  26 , a tip section  22 , a concave section  29 , and a leading section  216 . The four sections  26 ,  22 ,  29 , and  216  are smoothly connected in series, so as to form the profile of the longer tooth  27 . Similarly, the profile of the longer tooth  219  of the driven rotor  224  is connected smoothly by a convex section  218 , a tip section  215 , a concave section  221  and a leading section  23  on after another. The convex sections  26  and  218  refer to the edge curves of the longer teeth from the pitch circle to the tip section. The tip sections  22  and  215  refer to a curve section at the top of the longer teeth connecting the convex section and the concave section. The tip section of an external gear is farthest from the center of the pitch circle thereof. The concave sections  29 ,  221  refer to such curves that extend from the tip sections  22 ,  215  to the root portions of the longer teeth and concave toward to the convex sections of the longer teeth. The leading sections  216 ,  23  refer to such curves that extend from the root portions to the pitch circles  212 ,  222  respectively. The transition teeth refer to the first short tooth connecting the longer tooth to the shorter teeth and there are two types of transition teeth i.e., the convex transition teeth  217 ,  24  and the concave transition teeth  28 ,  220 . The convex section, the tip section, the concave section and the leading section can be connected smoothly by several sections of cycloids, lines, arcs, involutes and/or their envelope curves. The convex sections  26 ,  218  of the driving rotor  214  and the driven rotor  224  project into the outside of the pitch circle  212 ,  222 . The two sides of the longer tooth  27  of the driving rotor  214  are respectively provided with the transition teeth  217 ,  28  which adjoins the shorter teeth  210  in turn. The two sides of the longer tooth  219  of the driven rotor  224  are respectively provided with the transition teeth  24 ,  220  which adjoins the shorter teeth  225  in turn. When the driving rotor  214  rotates in the clockwise direction, during the longer tooth  27  of the driving rotor engages with the longer tooth  219  of the driven rotor, until the engaging point is changing from the convex section  26  of longer tooth of the driving rotor  214  to the concave section  216  of the longer tooth of the driving rotor, the tip section  22  of the longer tooth of the driving rotor begins to be in disengagement condition, so that during this engaging-point changing process, a reasonable contact ratio (multiple engaging point solution) is used, thus a smooth and constant run of the rotors is realized. That is, the leading section should enter into engagement in time just before the convex section is out of engagement, or the convex section should enter into engagement in time just before the leading section is out of engagement. The transition teeth comprise convex transition teeth  217 ,  24  and concave transition teeth  28 ,  220 . The convex transition tooth  217  of the driving rotor  214  is connected with the end point of the concave section  216  of the longer tooth. The concave transition tooth  28  is connected with the start point of the convex section  26  of the longer tooth. The convex transition tooth  24  of the driven rotor  224  is connected with the end point of the concave section  23  of the longer tooth. The concave transition tooth  220  is connected with the start point of the convex section  218  of the longer tooth. The convex transition tooth  217  of the driving rotor  214  and the concave transition tooth  220  of the driven rotor, having conjugate curves with respect to each other, can be in engagement with each other. The concave transition tooth  28  of the driving rotor and the convex transition tooth  24  of the driven rotor, with conjugate curves with respect to each other, can be in engagement with each other. The other shorter teeth are the conventional teeth as the prior art. 
     In operation, the driving rotor  214  rotates in the clockwise direction, so as to make the driven rotor  224  to rotate in the anti-clockwise direction. In a case, the concave transition tooth  28  of the driving rotor  214  engages with the convex transition tooth  24  of the driven rotor  224 . Then, the convex section  26  of the driving rotor  214  engages with the leading section  23  of the driven rotor  224 . After that, the leading section  216  of the driving rotor  214  engages with the convex section  219  of the driven rotor  224 . Then, the convex transition tooth  217  of the driving rotor  214  engages with the concave transition tooth  220  of the driven rotor  224 . Then, the ordinary shorter teeth of the one rotor begin to engage with the ordinary shorter teeth of the another rotor. In this process, the perfect seal effect and therefore the effective driving is realized. On the other hand, if the driven rotor  224  rotates in the clockwise direction so as to drive the driving rotor  214  to rotate in the anti-clockwise direction, the perfect seal effect and therefore the effective driving can also be realized 
     FIG. 2 shows one embodiment of the teeth profile of the driving rotor  214 . 
     The convex section  26  of the driving rotor  214 , i.e. the curve A 1 F 1 , is smoothly connected by a cycloid, a line, an arc and an envelope curve of lines, in which the section of E 1 F 1  is the cycloid, D 1 E 1  the line, C 1 D 1  the arc, and A 1 C 1  the envelope curve of the lines. The tip section  22 , i.e. the curve A 1 B 1 , is a cubic spline curve or an arc. The concave section  29 , i.e. the curve B 1 L 1 , is a cycloid which keeps engaging with a fixed point on the driving rotor or an envelope curve of arcs. The leading section  216 , i.e. the curve L 1 Q 1 , is smoothly connected by three curves, in which the section of L 1 M 1  is a line, M 1 P 1  an envelope curve of lines, and P 1 Q 1  a cycloid. On the profile of the concave transition tooth  28 , the curve F 1 G 1  is a cycloid, G 1 H 1  a part of root circle and H 1 I 1  an involute. On the profile of the protruding transition tooth  217 , the curve R 1 Q 1  is a cycloid, R 1 S 1  a part of addendum circle and S 1 T 1  an involute. The shorter teeth are ordinary involute teeth. 
     FIG. 3 shows one embodiment of the teeth profile of the driven rotor  224 . 
     The convex section  218  of the driven rotor  224 , i.e. the curve Q 2 L 2 , is smoothly connected by a cycloid, a line, and an envelope curve of several lines, in which the section of Q 2 P 2  is the cycloid, P 2 M 2  the line, and L 2 M 2  the envelope curve of the lines. The tip section  215 , i.e. the curve L 2 K 2 , is a small section of arc. The concave section  221 , i.e. the cure A 2 K 2 , is a cycloid which keeps engaging with a fixed point on the driving rotor or which is an envelope curve of arcs. The leading section  23 , i.e. the curve A 2 F 2 , is smoothly connected by four sections, in which the section of A 2 C 2  is a line, C 2 D 2  an arc, D 2 E 2  an envelope curve of the lines, and E 2 F 2  a cycloid. Regarding to the profile of the concave transition tooth  220 , the section of R 2 Q 2  is a cycloid, R 2 S 2  a part of the root circle, and S 2 T 2  an involute. Regarding to the profile of the convex transition teeth  24 , the section of F 2 G 2  is a cycloid, G 2 H 2  a part of the addendum circle, and H 2 I 2  an involute. The shorter teeth are ordinary involute teeth. 
     In FIG. 2, the convex section  26  of the driving rotor  214 , i.e. the section of A 1 F 1 , may have the following variant solution: the arc C 1 D 1  is omitted and the line D 1 E 1  is designed to be tangent both to the envelope curve A 1 C 1  of several lines and to the cycloid E 1 F 1 , so as to form another type of the convex section which is composed of a cycloid, a line and an envelope curve of several lines in series. The cycloid E 1 F 1  can also be replaced by an involute, in this case, the convex section is smoothly connected by an involute, a line, an arc, and an envelope curve of several lines in series. In addition, the cycloid E 1 F 1  may also be replaced by a parabola, in this case, the convex section of the longer tooth is smoothly connected by a parabola, a line, an arc and an envelope curve of several lines in series. The cycloid E 1 F 1  may also be replaced by a section of an ellipse, in this case, the convex section of the longer tooth is smoothly connected by a section of an ellipse, a line, an arc, and an envelope curve of several lines in series. Alternatively, the envelope curve A 1 C 1  of several lines may be replaced by a cycloid, in this case, the convex section of the longer tooth is smoothly connected by a cycloid, a line, an arc, and a cycloid in series. The envelope curve A 1 C 1  of several lines may also be replaced by a parabola, in this case, the convex section of the longer tooth is smoothly connected by a cycloid, a line, an arc, and a parabola in series. Alternatively, the envelope curve A 1 C 1  of several lines may also be replaced with a section of an ellipse, in this case, the convex section of the longer tooth is smoothly connected by a cycloid, a line, an arc, and a section of an ellipse in series. In addition, the envelope curve A 1 C 1  of several lines can be replaced with an arc and the arc C 1 D 1  is omitted, then the convex section of the longer tooth is smoothly connected by a cycloid, a line, and an arc in series. In this way, several profile variants of the convex section can be obtained. Similarly, the profile of the convex section  218  of the driven rotor may be modified in the same way as done for the profile of the convex section  26  of the driving rotor. 
     The gearing zone of a pair of the internal engaging gears is arranged in the central area of the “8”-shaped housing, i.e., with an appearance of a pair of twin cylinders inter-invaded to each other. The two ends of the housing are provided with the upper end cover and the lower end cover respectively. The end covers or the side wall of the housing are provided with through holes for suction and discharge of gas (air) or liquid, so as to form a complete gear-type mechanism, it is realized to compress the gas, to expand the gas, to transfer the fluid or colloid by means of the chambers enclosed by the longer teeth of the rotors, the engaging points, and the side walls of the housing together with the through holes for suction and discharge of gas (air) or liquid. 
     A preferred embodiment of the compressor according to the present invention will be described together with the FIGS. 4 to  7 . 
     The compressor according to the present invention is mainly composed of the gear-shaped rotors  214 ,  224  engaging with each other, the “8”-shaped housing  213 , the upper and the lower end covers  43 ,  44 . The shaft  211  of the driving rotor  214  and the shaft  21  of the driven rotor  224  are arranged to be parallel with each other. The axes of the two shafts are located in the centers of the two cylinders of the “8”-shaped housing respectively. The distance between the centers of the driving rotor  214  and the driven rotor  224  is equal to the sum of the radii of the two pitch circles  212  and  222  of the two rotors. The driving and driven rotors are provided with the shorter teeth  210 ,  225 , the convex transition teeth  217 ,  24 , the concave transition teeth  28 ,  220 , and the longer teeth  27 ,  219  on their pitch circles  212 ,  222  respectively. The profiles of the longer teeth of the driving and driven rotors are formed by smoothly connecting the convex sections  26 ,  218 , the tip sections  22 ,  215 , the concave sections  29 ,  221 , and the leading section  216 ,  23  respectively in series. The convex sections  26  and  218  refer to such curves that project from the pitch circles to the tip sections of the convex sections of the longer teeth respectively. The tip sections  22  and  215  refer to a curve section at the top of the longer teeth connecting the convex section and the concave section. The tip section of an external gear is farthest from the center of the pitch circle thereof. The concave sections  29 ,  221  refer to such curves that concave to the convex sections of the longer teeth and extend from the tip sections  22 ,  215  to the root portions of the longer teeth. The leading sections  216 ,  23  refer to such curves that extend from the root portions to the pitch circles  212 ,  222  respectively. The convex section, the tip section, the concave section, and the leading section are smoothly connected by several of the cycloids, the lines, the arcs, the involutes, and the envelope curves composed thereof. The convex sections  26 ,  218  project into the outside of the pitch circles  212 ,  222 . The two sides of the longer teeth  27 ,  219  of the driving and driven rotors are provided with the convex transition teeth  217 ,  24  and the concave transition teeth  28 ,  220  respectively, and the transition teeth further adjoin the shorter teeth  210 ,  225 , respectively. The upper and the lower end covers are in the shape of a plate, and they are arranged on the two ends of the housing  213  respectively. The gas discharge ports, i.e. gas (air) outlets  223 , which are in a shape of a section of a ring, are provided on the one or two end covers of the driven rotor  224 . In detail, the radius of the outer arc  42  of the air outlet is slightly shorter than the radius of the root circle of the shorter teeth of the driven rotor, while the radius of the inner arc  41  of the air outlet is larger than or equal to the minimum distance from the concave section of the longer tooth of the driven rotor to the axis thereof. The starting position of the air outlet  223  is set by a pre-determined pressure. The ending position of the air outlet is an arc whose center is the axis of the driving rotor and whose radius is the distance from the axis to the tip section of the longer tooth of the driving rotor. The air inlet  25  is located on the side wall of the housing. The axis of the air inlet  25  is on an imaging line connecting the two inflection points  410 ,  411  of the two cylinders of the “8”-shaped housing  213 . The driving rotor  214  rotates in the clockwise direction. When the tip section of the longer tooth of the driving rotor  214  rotates into the area of the air inlet  25 , the working chamber  226  enclosed by the walls of the housing and the upper and the lower end covers is divided into two closed elementary volumes by means of the longer teeth  27 ,  219  of the two rotors and the engaging points of the two rotors. One of the elementary volume becomes bigger and bigger and communicates with the air inlet  25 , so as to run in the suction process, while the other the elementary volume becomes smaller and smaller, then communicates with the air outlet  223 , so as to run in the compression and gas discharge process. As the driving rotor  214  rotates, each of the elementary volumes finishes a complete working process, that is, the processes of suction, compression and evacuation. When one elementary volume finishes a complete working process, that is, the processes of suction, compression and evacuation, the rotor needs to rotate an angle of 4π. Whenever the rotor rotates an angle of 2π, there is one process of suction and evacuation. In operation, no closed suction volume and closed evacuation volume are formed, and efficient suction is kept. 
     FIG. 5 is a schematic view of the whole structure of the gear-type compressor, in which the air inlet and air outlet of the upper end cover are provided with a sliding valve regulating means and the housing is provided with a liquid spraying aperture. 
     FIG. 6 is a schematic view of the whole structure of the gear-type compressor, in which the lower end cover is provided with an air inlet, an air outlet and a sliding valve regulating means, and the housing is provided with a liquid spraying aperture. 
     Since a gear-type compressor is a complete built-in compression machine, once the air inlet  231  has been designed, the evacuation pressure is determined only by the starting and ending positions of the air outlet  223 . When the evacuation pressure needs to be changed according to the working condition, the sliding valve  229  can be operated so as to regulate the starting and ending positions of the air outlet, and therefore regulate the final pressure of the built-in compression, so that the over compression can be avoided and energy consumption can be reduced. The gear-type compressor can be widely used under different working conditions and can always save energy. A concave sliding valve groove  230  in a shape of a section of a ring is provided on the upper end cover of the gear-type compressor, being near the inner surface of the housing. One end of the sliding valve groove  230  is communicated with the air outlet  223 . The radii of the inner arc  45  and the outer arc  46  of the sliding valve groove  230  are equal to the radii of the inner arc and the outer arc of the air outlet  223  respectively. The sliding valve groove  230  is provided with a sliding valve  229  in a shape of a section of a ring. The radii of the inner arc  47  and the outer arc  48  of the sliding valve  229  are equal to the radii of the inner arc and the outer arc of the air outlet  223  respectively. If a two-side discharge method is adopted, the area for gas discharging can be doubled, while the loss for gas discharging resistance can be reduced. In this case, the sliding valves can be provided on the two end covers, so as to be suitable to variant working conditions. The concave sliding valve grooves  230 ,  237  in a shape of a section of a ring are respectively provided on the upper and the lower end covers, being near to the inner surface of the housing. One end of the sliding valve grooves  230 ,  237  are communicated with the air outlet  223 ,  235 , respectively. The radii of the inner arc and the outer arc of the sliding valve groove  230 ,  237  are equal to the radii of the inner arc and the outer arc of the air outlet  223 ,  235  respectively. The sliding valve grooves  230 ,  237  are respectively provided with the sliding valves  229 ,  236  in a shape of a section of a ring. The radii of the inner arc and the outer arc of the sliding valve  229 ,  236  are equal to the radii of the inner arc and the outer arc of the air outlet  223 ,  235  respectively. When the discharge pressure needs to be increased, the sliding valves  229 ,  236  can be rotated in the anti-clockwise direction along the sliding valve grooves  230 ,  237 , so that the area of the air outlets  223 ,  235  becomes smaller and smaller, thus the final pressure of the built-in compression is enhanced. On the other hand, if the sliding valves  229 ,  236  are rotated in the clockwise direction, the final pressure of the built-in compression will be reduced. The air inlet, i.e. the gas absorbing port, can be arranged in various solutions. According to one of the solutions, the air inlet  25  is arranged on the side wall of the housing  213 . In this solution, the axis of the air inlet  25  is located to coincide an imaging line between the two inflection points of the “8”-shaped housing  213 . In many cases, the gas transferring amount is required to be able to be regulated, that is, variable volume regulation is required. Especially, the capability of variable volume regulation is very important for the compressor of the air-conditioner for the automobiles. By setting sliding valve in the air inlet, the gear-type compressor can conveniently realize the variable volume regulation, nearly no power loss, and even can realize a stepless regulation. In this case, the air inlet  231  is provided on an end cover which is the so called upper end cover. The radius of the radially inner arc  412  of the air inlet  231  is equal to or slightly smaller than the root circle of the shorter teeth of the driving rotor. The radius of the radially outer arc  413  of the air inlet  231  is slightly smaller than that of the inner radius  49  of one end of the cylinder on the side of the driving rotor  214 . A concave sliding valve groove  233  in a shape of a section of a ring is provided on the upper end cover, being near the inner surface of the housing. One end of the sliding valve groove  233  is communicated with the air inlet  231 . The radii of the inner arc  414  and outer arc  415  of the sliding valve groove  233  are equal to the radii of the inner arc and outer arc of the air inlet  231  respectively. A sliding valve  232  in a shape of a section of a ring is provided on the sliding valve groove. The radii of the inner arc  416  and outer arc  417  of the sliding valve  232  are equal to the radii of the inner arc and outer arc of the air inlet  231  respectively. When the gas transferring volume needs to be reduced, the sliding valve  232  of the air inlet can be rotated in the clockwise direction, so as to make the area of the air inlet  231  becomes bigger and bigger, thus the elementary volume of compression and evacuation, which is formed when the tip sections of the two longer teeth  27 ,  219  passes the inflection point of the “8”-shaped housing, is still communicated with the air inlet  231 . As a result, the working medium, which has entered into the elementary volume of compression and evacuation, partially backflows from air inlet  231 , so that the working medium compressed in one working cycle is reduced, thus the variable volume regulation can be realized. If the upper and the lower end covers are both provided with sliding valves regulating means, the range of volume regulation will be wider. In an embodiment, the regulating means of the upper end cover is not changed, while an air inlet  238  in a shape of a section of a ring and a sliding valve groove  240  in a shape of a section of a ring are provided on the lower end cover. The radii of the inner arc and outer arc of the air inlet  238  are equal to the radii of the inner arc and outer arc of the air inlet in the upper end cover. The starting position  241  of the air inlet of the lower end cover is slightly located before the ending position  234  of the air inlet of the upper end cover. The sliding valve groove  240  is provided with a sliding valve  239  in a shape of a section of a ring. The gas transferring volume can be further regulated by regulating the location of the sliding valve  239 . The sliding valves in the upper and the lower end covers cab be cooperated with each other, so that the gear-type compressor can have a wide range of volume regulation, so as to be able to be used in different conditions. 
     FIG. 7 shows an air inlet arrangement solution. An air inlet  242  in a shape of a section of a ring is provided on one end cover. The air inlet is provided on the end cover on the side of the driving rotor  214 . The radius of the inner arc of the air inlet is slightly shorter than the radius of the root circle of the shorter teeth of the driving rotor  214 . The radius of the inner arc of the air inlet is equal to the minimum distance from the leading section of the longer tooth of the driving rotor to the axis of the driving rotor. In the gear-type compressor, clearances are provided between the side surfaces and the end covers and between the tip sections of the longer teeth and the inner surface of the housing, as a result, the fluid leakage through the clearances cannot be prevented. As shown in FIG. 5, liquid spraying apertures  227 ,  228  are provided on the side wall of the housing. By means of using the liquid spraying technique, the fluid leakage, through the clearances can be greatly reduced, while generated noise is also reduced and a good lubrication effect is obtained. As the liquid spraying reduces the temperature in the compressor and the power loss of the compressor, the single-stage compression ratio can be greatly improved. 
     FIG. 8 is a schematic view showing the structure of the rotors which are a pair of inner gearing gears according to the present invention. According to another embodiment of the present invention, the fluid machine includes an internal gear  31  and an external gear  34 . The internal gear  31  works as the driven rotor, while the external gear  34  works as the driving rotor. The shaft  35  of the driving rotor  34  and the shaft the driven rotor are arranged to be parallel with each other. The distance between the axes of the driving rotor  34  and the driven rotor  31  is equal to the radius difference of the pitch circles  32 ,  313  of the two rotors. The driving rotor  34  is provided with shorter teeth  314 , a convex transition teeth  36 , a concave transition teeth  312  and a longer tooth  310 . The cross-section of the longer tooth  310  of the driving rotor  34  is of a hawk beak shape, and the profile thereof is smoothly connected by a convex section  311 , a tip section  39 , a concave section  38 , and a leading section  37  in series. The convex sections  311  refers to such a convex curve that extends from the pitch circle  313  of the longer tooth  310  to the tip section thereof. The concave section  38  refers to such a concave curve that extends from the tip section  39  to the root portion of the longer tooth. The tip section  39  refers to a curve section at the top of the longer tooth connecting the convex section and the concave section. The tip section of an external gear is farthest from the center of the pitch circle thereof. The leading section  37  refers to such a curve that extends from the root portion of the longer tooth to the pitch circles  313  thereof. The transition teeth refer to the first short tooth connecting the longer tooth to the shorter teeth, and there are two types of transition teeth, i.e., the convex transition tooth  36  and the concave transition tooth  312 . The convex section  311  of the external gear, i.e. the driving rotor  34 , projects into the outside of the pitch circle  313 . The two sides of the longer tooth  310  are respectively provided with the convex transition tooth  36  and the concave transition tooth  312 . The convex transition tooth  36  and the concave transition tooth  312  adjoin the shorter teeth  314  in turn. The driven rotor, i.e. the internal gear  31 , is provided with shorter teeth  33 , a convex transition teeth  321 , a concave transition teeth  315 , and a longer tooth  317 . The cross-section of the longer tooth  317  of the internal gear  31  is of a hawk beak shape, and the profile of the longer tooth  317  is smoothly connected by a convex section  316 , a tip section  318 , a concave section  319 , and a leading section  320  in series. The convex sections  316  of the internal gear  31  refers to such a convex curve that extends from the pitch circle of the longer tooth  310  to the tip section  318  thereof. The concave section  319  refers to such a concave curve that extends from the tip section  318  to the root portion of the longer tooth. The tip section  318  refers to a curve section at the top of the longer tooth connecting the convex section and the concave section. The tip section of an internal gear is nearest from the center of the pitch circle thereof. The leading sections  320  refers to such a curve that extends from the root portion of the longer tooth to the pitch circle  32 . The transition teeth refer to the first short tooth connecting the longer tooth to the shorter teeth, and there are two types of transition teeth, i.e., the convex transition tooth  321  and the concave transition tooth  315 . The convex section  316  of the internal gear  31  projects into the inside of the pitch circle  32 , while the leading section  320  recesses into the outside of the pitch circle  32 . The two sides of the longer tooth  317  are respectively provided with the convex transition tooth  321  and the concave transition tooth  315 . The convex transition tooth  321  and the concave transition tooth  315  adjoin the shorter teeth  33  in turn. The convex section, the tip section, the concave section, and the leading section are all smoothly connected by several sections of cycloids, lines, arcs, involutes and envelope curves thereof. 
     The convex section  311  of the longer tooth  310  of the external gear  34  and the leading sections  320  of the longer tooth  317  of the external gear  31 , as conjugate curves, engages with each other. The leading sections  37  of the longer tooth  310  of the external gear  34  and the convex section  316  of the longer tooth  317  of the external gear  31 , as conjugate curves, engages with each other. The profiles of the two sides of the transition teeth are different. The shorter teeth are ordinary teeth of the conventional gear. 
     When the driving rotor  34  rotates in the clockwise direction, the longer tooth  310  of the driving rotor engages with the longer tooth  317  of the driven rotor  31 . In the case that the engagement point reaches the leading section  37  of the longer tooth of the driving rotor  34 , the engagement line is broken at the tip section  39  of the longer tooth of the driving rotor  34 . During such operation, the reasonable contact ratio can make the gears transmit power or driving force smoothly and constantly. That is, the leading section must enter into engagement in time just before the convex section is out of engagement, or the convex section must enter into engagement in time just before the leading section is out of engagement. Then, the convex transition tooth  36  of the driving rotor  34  engages with the concave transition tooth  315  of the driven motor. The shorter teeth engage with each other so as to form a perfect sealing effect and transmit power or driving force. 
     During rotors rotates in engagement with each other, a seal effect is realized along the engaging lines between a shorter tooth of one rotor and a transition tooth of the other rotor. When the rotors rotates, it is more important that a seal effect for the working medium in the working chamber is also realized between the longer tooth  317  of the internal gear  31  and the longer tooth  310  of the internal gear  34  with benefits of the shape of a hawk beak. Especially, it can be realized for such a pair of rotors to compress, expand and transfer the fluids. 
     FIG. 9 shows one embodiment of the profile of the teeth of the external gear. 
     The convex section  311  of the longer tooth  310  of the driven rotor  34 , i.e. the curve I 2 M 2 , is smoothly connected by a cycloid, a line, an arc, and an envelope curve of several lines, in which the section of M 2 L 2  is the cycloid, L 2 K 2  the line, K 2 J 2  the arc, and I 2 J 2  the envelope curve of the lines. The tip section  39 , i.e. the curve A 2 I 2 , is an arc. The concave section  38 , ie. the curve B 2 A 2 , is a curve composed of a cycloid and arcs, the cycloid being such one that keeps engaging with a fixed point on the driving rotor. The leading section  37 , i.e. the curve B 2 E 2 , is in series connected by a line, an arc, and an envelope curve of another several lines, in which the section of B 2 C 2  is the line, C 2 D 2  the arc, and D 2 E 2  is the envelope curve of the another several lines. Regarding to the profile of the convex transition teeth  36 , the section of E 2 F 2  is a cycloid, F 2 G 2  a part of addendum circle, and H 2 G 2  an involute. On the concave transition tooth  312 , the section of M 2 N 2  is a cycloid, O 2 N 2  a part of root circle, and O 2 P 2  an involute. The shorter teeth are ordinary involute teeth. 
     FIG. 10 shows one embodiment of the profile of the teeth of the internal gear  31 . The convex section  316  of the longer tooth  317  of the internal gear  31 , i.e. the curve B 1 E 1 , is smoothly connected in series by a line, an arc, and an envelope curve of another several lines, in which the section of B 1 C 1  is the envelope curve of several lines, C 1 D 1  the arc, D 1 E 1  the envelope curve of another several lines. The tip section  318  of the longer tooth  317 , i.e. the curve A 1 B 1 , is the arc. The concave section  319 , i.e. the curve A 1 I 1 , is a point-engaging forming cycloid. The leading section  320 , i.e. the curve I 1 M 1 , is smoothly connected in series by a line, an arc, an envelope curve of another several lines, and a cycloid, in which the section of I 1 J 1  is the line, J 1 K 1  the arc, K 1 L 1  is the envelope curve of the lines, and L 1 M 1  the cycloid. Regarding to the profile of the convex transition tooth  321 , the section of M 1 N 1  is a cycloid, O 1 N 1 , a part of addendum circle, and O 1 P 1  an involute. On the concave transition tooth  315 , the section of E 1 F 1  is a cycloid, F 1 G 1 , an arc, a part of root circle, and H 1 G 1  an involute. The shorter teeth are ordinary involute teeth. 
     The pair of the internal engaging gears are arranged within a cylindrical body. A shim in the shape of a part of moon is provided in the space for the two rotors&#39; rotation. The upper end cover  51  and the lower end cover  52  are respectively installed at the two ends of the cylinder. The end covers are provided with through holes for fluid suction and evacuation. In this way, a complete internal engaging gear-type fluid machine is formed, so as to compress, expand, and convey the fluids. 
     FIG. 11 is a schematic view of one embodiment of the internal engaging gear-type compressor. The shim  324  in the shape of a part of moon, the external gear  34 , and the internal gear  31  are all arranged within the cylindrical body  323 . An air inlet  326  is defined by the addendum circle  57  of the shorter teeth of the internal gear, the addendum circle of the shorter teeth of the external gear, and a line passing through the lower tip section  327  of the shim. An air outlet  325  is arranged on the end cover, and located between the root circle  56  of the shorter teeth  33  of the internal gear  31  and the root circle  55  of the longer tooth  317 . That is, the radius of the inner arc  53  of the air outlet is equal to or larger than the radius of the root circle of the shorter teeth of the driven rotor, and the radius of the outer arc  54  of the air outlet is equal to or smaller than the radius of the root circle of the longer tooth of the driven rotor. An elementary volume is enclosed by the longer teeth  317 ,  310  of the two rotors, the shim  324  in the shape of a part of moon, and the engaging point of the two rotors. When the longer tooth  310  of the external gear  34  rotates so as to reach to the lower tip section  327  of the shim  324  in the shape of a part of moon, the closed elementary volume is formed, so that the gas can be compressed. When the longer teeth  317 ,  310  of the longer teeth of the two rotors rotates so as to reach to the upper tip section  328  of the shim  324  in the shape of a part of moon, the two longer teeth and the upper tip section  328  of the shim  324  begin to be in their engagement with one another simultaneously, thus a perfect seal effect is realized in the upper tip section  328  of the shim  324 . When the leading section of the longer tooth of the internal gear  31  rotates to pass the air outlet  325 , the gas begin to discharge from the elementary volume. In this way, a complete working cycle, i.e., suction, compression and evacuation, is realized. 
     By means of sliding valves provided on the gas discharging port (air outlet) and the gas absorbing port (air inlet), the variable working conditions and the variable gas transferring volume can be conveniently regulated. 
     FIG. 12 is a schematic view of the internal engaging gear-type compressor, in which sliding valves are provided. By moving the sliding valve  329  along the sliding valve groove  330 , the air outlet  325  may be opened to be wider or narrower, so that a stepless regulation is realized, so as to be suitable to variable working conditions. 
     The fluid machine according to this invention can also be used as an expansion machine. 
     This invention is directed to use minimum components to solve the problems on the seal effect and the transmission reliability of rotary fluid machines, so as to effectively compress, expand, and transfer the fluids. 
     According to this invention, among every curve sections of the longer tooth in the shape of a hawk beak, the convex section and the leading section is used to transmit power and to seal the fluids, while the tip section and the concave section is used to seal the fluids within a desired working chamber. 
     The preferred embodiments of the present invention have been described in detail together with the accompanying drawings. However, the present invention is not limited to the preferred embodiments. Those skilled in the art will appreciate that various modifications, substitutions and improvements are possible without departing from the scope and spirit of the invention. 
     For example, the gear according to this invention may be provided with only one longer tooth, but it can also be provided with two or more longer teeth. 
     Especially, the longer teeth can be even distributed along the circumferential direction. 
     Moreover, according to this invention, more than two gears with at least one longer tooth can be arranged in the expansion machine or the compressor. The radii of such gears can be same as or different to each other. 
     Although the teeth of the above embodiments are all spur teeth, they can be made as helical or herringbone teeth. 
     Moreover, the gear according to this invention not only can be a columnar gear, but also can be a bevel gear. 
     Furthermore, the gear according to this invention not only can be a circular gear, but also can be a non-circular gear. 
     As stated above, the gear according to this invention not only can be an external gear, but also can be an internal gear. 
     Moreover, in the fluid machine according to this invention, a pair of engaging gears can be both the external gears, but they can also be one external gear and one internal gear. 
     By means of regulating the rotating speed of rotors, such as by using different frequencies, the fluid machine according to this invention can also have variable gas transfer volumes. 
     In addition, in the fluid machine according to this invention, a clearance can be arranged between the engaging points of a pair of engaging gears, so the machine can be used in such industrial fields that its products such as the food and the textile cannot be contaminated by the lubricating oil. In the case, this pair of engaging gears is driven by other separate synchronizing gears. 
     INDUSTRIAL APPLICABILITY OF THIS INVENTION 
     This invention can be applied into a wide range of the industrial fields such as the compressor, the pump, the fluid measurement, the hydraulic motor, and the compact machines.