Abstract:
To provide an internal gear pump capable of preventing small vibrations due to pressure differences at the outlet port side of a crescent disposed between the outer rotor and the inner rotor, so that fatigue failure does not occur in the crescent over a long time period, whereby the durability can be increased. The internal gear pump includes a rotor unit, in which an inner rotor is disposed within an outer rotor on the inner peripheral side and a crescent is disposed in the gap between the inner rotor and the outer rotor, the rotor unit being housed in a pump casing. Outer cells are formed by the crescent and the outer rotor. Inner cells are formed by the crescent and the inner rotor. Linking of the outer cells and the outlet port, and linking of the inner cells  6  and the outlet port, start substantially simultaneously.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an internal gear pump capable of preventing small vibrations generated in the crescent disposed between the outer rotor and the inner rotor due to pressure differences at the outlet port, so that fatigue failure of the crescent does not occur over a long period of time, and the durability is increased. 
         [0003]    2. Description of the Related Art 
         [0004]    Internal gear oil pumps frequently use trochoid-shaped rotors. Using trochoid-shaped gear teeth has the advantages that the inner and outer rotors are in rolling contact, so gear impact noise is small, and cavitation does not easily occur. Also, the height of the tooth (from the base to the top) can be made large, which has the advantage that the flow rate can be increased. On the other hand, however, with trochoid-shaped rotors the space between gear teeth (cells) is sealed by the line contact of the inner tooth form contacting the outer tooth form. Therefore, pressure is lost from the line contact portion to adjacent cells, there is the disadvantage that the pressure generated is not very high. Furthermore, for smooth rolling, there is a very small gap between the inner tooth form and the outer tooth form, and this is also a cause of loss of pressure. Also, there is a type of pump known as a crescent pump, in which a part known as the crescent is disposed between the inner rotor and outer rotor. In this form, there is line contact at a plurality of locations between the rotor teeth and the fixed crescent, so pressure cannot easily escape to adjacent cells. This has the advantage that a higher pressure can be generated compared with the normal internal gear pump with no crescent. Also, in conventional crescent pumps normal gears, in other words gears with comparatively low teeth, are generally used, so pressure fluctuations are not much of a problem. However, in recent years the requirements for greater efficiency and performance are increasing. In response to these requirements usually performance (flow rate) is improved by increasing the height of the teeth, and reducing the number of teeth. However, crescent pumps have the disadvantage that when the height of the teeth is increased and the number of teeth is reduced, outlet vibrations and cavitation can more easily occur. 
         [0005]    As a result, by trying to improve the flow rate with trochoid gear teeth form, for which the gear impact noise is low, cavitation does not easily occur, and the height of the teeth can be formed larger, there is a danger of occurrence of fatigue failure of the crescent due to small vibrations generated by pressure fluctuations when the flow rate is high. Therefore, it was very difficult to achieve high performance with gear rotors with high teeth, in particular in pumps whose structure combined trochoid-shaped teeth rotors, for which the height of the teeth can be increased compared with normal gears, with a crescent. The more that performance (flow rate) was increased the more the fatigue failure problem increased. For example, as disclosed in Japanese Patent Application Laid-open No. S59-131787, with rotors whose tooth form approximated circular arcs at the top and the base of the teeth, the space between teeth (cells) in the parts approximated by circular arcs is narrower than the space between teeth with normal trochoid curves. Therefore the quantity of oil that can be delivered in one revolution is reduced, and the performance (flow rate) is reduced accordingly. However, the resulting pressure fluctuations are small, so conventionally this was not such a big problem, but high efficiency, high performance pumps using trochoid rotors is a big problem. 
         [0006]    Furthermore, in that internal gear pump, there is a slight time difference between the timing that the cells formed between the inner rotor and the crescent and the cells formed between the outer rotor and the crescent link with the outlet port. In other words, in an internal gear pump, the rotation speeds of the outer rotor and the inner rotor are different. The rotation speed of the inner rotor is faster than the rotation speed of the outer rotor. Therefore, normally the time that the top of a tooth of the inner rotor separates from the crescent does not coincide with the time that the top of a tooth of the outer rotor separates from the crescent. Therefore, the time that the fluid in a cell on the outside of the crescent flows into the outlet port does not coincide with the time that the fluid in a cell on the inside of the crescent flows into the outlet port. Because one of these cells is first to link with the outlet port, a pressure difference arises between the cell on the inside of the crescent and the cell on the outside of the crescent. 
         [0007]    This pressure difference causes small vibrations to occur in the crescent. These small vibrations could cause fatigue failure in the crescent. This phenomenon arises regardless of the shape of the teeth. It is considered that with trochoid-shaped teeth the extent of the outlet vibrations is small, but in internal gear pumps that use a crescent this problem can easily arise. 
       SUMMARY OF THE INVENTION 
       [0008]    Japanese Patent Application Laid-open No. S54-30506 is a pump that solves this problem with crescents in internal gear pumps. Here an invention is disclosed in which linking grooves are provided from the outlet port to the inside and outside of the crescent, so that the pressure difference between the inside and outside of the crescent is minimized. According to the technical details of this invention, a through hole is formed in the filler piece (a member that corresponds to the crescent), and grooves are formed in the pump body. 
         [0009]    However, when the grooves are provided, oil can flow backwards along the groove, so the flow rate could be reduced. Also, forming the through hole in the filler piece increases the number of manufacturing operations of the component, which increases the cost. Therefore, the task that the present invention aims to solve (the technical task or object) is to provide a pump with an extremely simple structure, that uses a crescent combined with rotors (including trochoid gear teeth rotors) with comparatively high gear teeth as in a trochoid rotor. Also, by optimizing the shape of the port to prevent the occurrence of pressure fluctuations, to provide a crescent pump that can use trochoid rotors and is capable of high performance, having a crescent with good durability and long life. 
         [0010]    Therefore, as a result of diligent research by the inventors to solve this problem, the invention according to claim  1  solves this problem with an internal gear pump having therein a rotor unit, in which an inner rotor is disposed on an inner peripheral side of an outer rotor and a crescent is disposed in a gap between the inner rotor and the outer rotor, in a pump casing, wherein linking of an outlet port in the pump casing to outer cells formed by the crescent and the outer rotor, and linking of the outlet port to inner cells formed by the crescent and the inner rotor start substantially simultaneously. 
         [0011]    The invention according to claim  2  solves this problem with an internal gear pump comprising a pump casing, an outer rotor, an inner rotor, and a crescent disposed between the outer rotor and the inner rotor, wherein the start of separation of the crescent and the top of each tooth of the outer rotor, and the start of separation of the crescent and the top of each tooth of the inner rotor occur substantially simultaneously, and linking to an outlet port occurs at the start of separation. 
         [0012]    The invention according to claim  3  solves this problem with an internal gear pump according to the configuration described above, wherein a port projection portion, formed in an outer peripheral side of a starting end portion of the outlet port, projects along a circumferential direction and extends across the area over which the tooth top portions of the outer rotor, and a position of an end of the port projection portion is a position at which the top of each tooth of the outer rotor starts to separate from the crescent. Next, the invention according to claim  4  solves this problem with an internal gear pump according to the configuration described above, wherein the continuity area of the port projection portion and the non-projecting starting edge of the outlet port substantially coincides in shape with the end portion on an outer peripheral side of the crescent. The invention according to claim  5  solves this problem with an internal gear pump according to the configuration described above, wherein the teeth of the outer rotor and the inner rotor are in trochoidal form. 
         [0013]    [Effects of the Invention] 
         [0014]    According to the invention of claim  1 , linking of the outlet port within the pump casing and the outer cells formed by the crescent and the outer rotor, and linking of the outlet port with the inner cells formed by the crescent and the inner rotor starts approximately simultaneously, so it is possible to make the fluid flow simultaneously into the outlet port from the outer cells and the inner cells on both the outside and the inside of the crescent. Therefore it is possible to eliminate the difference in pressure of the fluid in the outer and inner cells. In this way, only uniform pressure acts over the crescent as a whole, and unstable pressure is not applied, so small vibrations are not generated in the crescent. Therefore the durability and the life of the oil pump is improved. 
         [0015]    The invention according to claim  2  is an internal gear pump in which the start of separation of the crescent and the top of the teeth of the outer rotor and the start of separation of the crescent and the top of the teeth of the inner rotor occurs approximately simultaneously. Also, linking with the outlet port occurs when separation starts. Therefore the top of a tooth of the outer rotor and the top of a tooth of the inner rotor simultaneously separate from the crescent, and linking with the outlet port occurs. Therefore the fluid pressure in the outer cell and the inner cell that are linked to the outlet port is the same, so it is possible to prevent small vibrations in the crescent. Therefore the durability and life of the oil pump is improved, similar to the invention according to claim  1 . 
         [0016]    The invention according to claim  3  is an internal gear pump wherein a port projection portion is formed in the outer peripheral side of the starting portion of the outlet port, the port projection portion projects along the circumferential direction and extends across the area over which the tops of the teeth pass, and the position of the end of the port projection portion is the position at which the tops of the teeth of the outer rotor start to separate from the crescent. Therefore there is no particular need to carry out processing on the crescent. 
         [0017]    Moreover, the very simple structure of only forming the port projection portion in the outlet port may be adopted. Moreover, there is no need to carry out any processing on the crescent, or provide linking grooves or similar, so it is possible to prevent the reduction in flow rate. Furthermore, the port projection portion only is formed in the outlet port, so this can be adequately achieved with the mold. Therefore it is possible to reduce the manufacturing cost by eliminating processing. 
         [0018]    In the invention according to claim  4 , the shape of the continuity area of the port projection portion and the non-projecting starting edge of the outlet port is similar to and approximately coincides with the shape of the end portion of the outer side of the crescent. In the invention according to claim  5 , the teeth of the outer rotor and the inner rotor are in trochoidal form. Therefore it is possible to form the height of the teeth of the outer rotor and the inner rotor higher than the teeth of a normal gear pump. Therefore it is possible to increase the capacity of the cells formed by the crescent and the outer rotor and the inner rotor. Therefore it is possible to increase the flow rate that can be delivered at one time, so the efficiency of the pump can be improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1A  is a plan view showing the structure of the present invention; 
           [0020]      FIG. 1B  is a plan view showing the rotor chamber and the inlet and outlet ports of the pump housing; 
           [0021]      FIG. 2  is an enlarged plan view of the outlet port; 
           [0022]      FIG. 3A  is an enlarged transverse plan view showing the state in which the cell on the outside and the cell on the inside have not linked with the outlet port; 
           [0023]      FIG. 3B  is an enlarged transverse plan view showing the state in which the cell on the outside and the cell on the inside have linked with the outlet port; 
           [0024]      FIG. 4A  is an enlarged transverse plan view showing the state in which the top of the gear tooth of the outer rotor and the inner rotor are in contact with the arc-shaped convex surface side and the arc-shaped concave side of the crescent; and 
           [0025]      FIG. 4B  is an enlarged transverse plan view showing the state in which the top of the gear tooth of the outer rotor and the inner rotor have simultaneously started to separate from the arc-shaped convex surface side and the arc-shaped concave side of the crescent. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    The following is an explanation of the embodiments of the present invention based on the drawings. The structure of the present invention includes mainly a pump casing  1 , an outer rotor  2 , an inner rotor  3 , and a crescent  4 , as shown in  FIG. 1A . As shown in  FIG. 1B , a rotor chamber  11 , an inlet port  12 , and an outlet port  13  are formed in the pump casing  1 . Also, the inlet port  12  and the outlet port  13  connect with the flow path outside the pump casing  1 . Also, the pump casing  1  is used with a pump cover, which is not shown in the drawings. 
         [0027]    The inlet port  12  includes a starting portion  12   a  and a finishing portion  12   b.  Also, the outlet port  13  includes a starting portion  13   a  and a finishing portion  13   b  (see  FIG. 1B ). The starting portions  12   a,    13   a  of the inlet port  12  and the outlet port  13  are the sides from which tops of teeth  21  and  31 , which are described later, enter, and the finishing portions  12   b,    13   b  are the sides from which the tops of the teeth  21  and  31  exit, when the outer rotor  2  and the inner rotor  3  rotate. 
         [0028]    Next, as shown in  FIG. 1A , the outer rotor  2  is formed in a ring shape. On the inside of the outer rotor  2  the plurality of tooth top portions  21  is formed, and tooth base portions  22  are formed between adjacent tooth top portions  21 . On the outer periphery of the inner rotor  3  the plurality of tooth top portions  31  is formed, and between adjacent tooth top portions  31  tooth base portions  32  are formed. The outer rotor  2  is disposed to the outer peripheral side of the inner rotor  3 , and the tooth top portions  31  of the inner rotor  3  mesh with the tooth base portions  22  of the outer rotor  2 . 
         [0029]    The number of tooth top portions  31  on the inner rotor  3  is fewer than the number of tooth top portions  21  in the outer rotor  2  by a factor of two or more. The outer rotor  2  is rotatably supported by the inner peripheral wall  11   a  of the rotor chamber  11 , so that the position of the center of the outer rotor  2  is fixed with respect to the rotor chamber  11 . Also, the inner rotor  3  is fixed to a drive shaft that penetrates the rotor chamber  11 , and is rotated by the drive shaft. Also, the inner rotor  3  is disposed to the inside of the outer rotor  2  so that the center of the inner rotor  3  is eccentric to the center of the outer rotor  2 , and so that the tooth top portions  31  of the inner rotor  3  are set to mesh with the tooth base portions  22  of the outer rotor  2 . The arrow symbol in the circumferential direction shown in  FIGS. 1A ,  3 , and  4  indicates the direction of rotation of the outer rotor  2  and the inner rotor  3 . Also, the teeth on the outer rotor  2  and the inner rotor  3  are formed as trochoidal-shaped teeth. In other words, the tooth top portions  21  and the tooth base portions  22  of the outer rotor  2  are formed in a trochoidal shape. Also, the tooth top portions  31  and the tooth base portions  32  of the inner rotor  3  are formed in a trochoidal shape, so that they mesh with the tooth top portions  21  and the tooth base portions  22 . Also, the outer rotor  2  and the inner rotor  3  are not limited to trochoidal tooth forms; other types of tooth shape may be used. 
         [0030]    Next, as shown in  FIG. 1A , the crescent  4  is inserted and disposed in a gap S formed between the outer rotor  2  and the inner rotor  3 . The gap S is the approximately crescent moon-shaped space formed between the inside of the outer rotor  2  and the outer periphery of the inner rotor  3 . The crescent  4  has an approximately crescent moon-shape or an arc shape, that includes an arc-shaped convex surface side  41  and an arc-shaped concave surface side  42 . The crescent  4  is housed in the gap S, with the tooth top portions  21  and  31  in contact with the arc-shaped convex surface side  41  and the arc-shaped concave surface side  42  of the crescent  4  respectively. Also, one end of the crescent  4  is disposed near the finishing portion  12   b  of the inlet port  12 , and the other end of the crescent  4  is disposed near the starting portion  13   a  of the outlet port  13 . 
         [0031]    The tooth top portions  21  of the outer rotor  2  contact the arc-shaped convex surface side  41  of the crescent  4 , and form void portions in the space enclosed by the arc-shaped convex surface side  41  and the tooth base portions  22 . These void portions are referred to as cells. In particular the cells formed by the tooth base portions  22  of the outer rotor  2  and the arc-shaped convex surface side  41  are referred to as outer cells  5 . In the same way, the tooth top portions  31  of the inner rotor  3  contact the arc-shaped concave surface side  42  of the crescent  4 , and form void portions in the space enclosed by the arc-shaped concave surface side  42  and the tooth base portions  32 . These void portions are referred to as inner cells  6  (see  FIG. 1A ). 
         [0032]    When the inner rotor  3  is rotated by the drive shaft, the outer rotor  2  rotates. As the outer rotor  2  rotates, near the finishing portion  12   b  of the inlet port  12 , the tooth top portions  21  move from one end in the length direction of the arc-shaped convex surface side  41  of the crescent  4  towards the other end in the length direction while contacting the arc-shaped convex surface side  41  (see  FIGS. 3A ,  4 A). The tooth top portions  21  gradually separate from the surface of the arc-shaped convex surface side  41  of the crescent  4  near the other end in the length direction (see  FIGS. 3B ,  4 B). As the tooth top portions  21  separate from the arc-shaped convex surface side  41 , the outer cells  5  link with the outlet port  13 , the fluid in the outer cells  5  flows into the outlet port  13 , and the fluid is discharged. 
         [0033]    In the same way, as the inner rotor  3  rotates, near the finishing portion  12   b  of the inlet port  12 , the tooth top portions  31  move from one end in the length direction of the arc-shaped concave surface side  42  of the crescent  4  towards the other end in the length direction while contacting the arc-shaped concave surface side  42  (see  FIGS. 3A ,  4 A). The tooth top portions  31  gradually separate from the surface of the arc-shaped concave surface side  42  of the crescent  4  near the other end in the length direction (see  FIGS. 3B ,  4 B). As the tooth top portions  31  separate from the arc-shaped concave surface side  42 , the inner cells  6  link with the outlet port  13 , the fluid in the inner cells  6  flows into the outlet port  13 , and the fluid is discharged. 
         [0034]      FIG. 4A  shows the state just before the tooth top portion  21  of the outer rotor  2  and the tooth top portion  31  of the inner rotor  3  start to separate from the crescent  4 . Both the tooth top portion  21  of the outer rotor  2  and the tooth top portion  31  of the inner rotor  3  are in contact with the arc-shaped convex surface side  41  and the arc-shaped concave surface side  42  of the crescent  4  respectively, forming sealed (including approximately sealed) outer cells  5  and inner cells  6 . 
         [0035]      FIG. 4B  shows the instant that the tooth top portion  21  of the outer rotor  2  and the tooth top portion  31  of the inner rotor  3  start to simultaneously (including approximately simultaneously) separate from the arc-shaped convex surface side  41  and the arc-shaped concave surface side  42  of the crescent  4 . The fluid filling the outer cell  5  and the inner cell  6  simultaneously (including approximately simultaneously) flows into the outlet port  13 .  FIG. 4B  shows that the dimension δa of the gap between the tooth top portion  21  of the outer rotor  2  and the arc-shaped convex surface side  41  of the crescent  4  and the dimension δb of the gap between the tooth top portion  31  of the inner rotor  3  and the arc-shaped concave surface side  42  of the crescent  4  are the same (including approximately the same). 
         [0036]    Also, the time that the outer cell  5  starts to link with the outlet port  13  is the same (including approximately the same) as the time that the inner cell  6  starts to link with the outlet port  13 . Here, perfectly simultaneous is ideal, but approximately simultaneous is included in the concept of simultaneous. Approximately simultaneous indicates a very small time difference. In other words, a very small time difference between the time that the outer cell  5  and the inner cell  6  start to link with the outlet port  13  is equivalent to the time difference for which the fluid pressure difference between the outer cell  5  and the inner cell  6  is almost zero. 
         [0037]    In this way, at the position of the starting portion  13   a  of the outlet port  13 , the tooth top portion  21  of the outer rotor  2  and the tooth top portion  31  of the inner rotor  3  simultaneously separate from the arc-shaped convex surface side  41  and the arc-shaped concave surface side  42  of the crescent  4 . The outer cell  5  and inner cell  6  simultaneously link with the outlet port  13 . As shown in  FIG. 3B and 4B , the fluid filling the outer cell  5  and the inner cell  6  simultaneously flows into the outlet port  13 , so the difference in the internal pressure of the outer cell  5  and the inner cell  6  immediately after starting to link with the outlet port  13  is eliminated. In other words, the difference in pressure on the arc-shaped convex surface side  41  and the arc-shaped concave surface side  42  of the crescent  4  is eliminated, so it is possible to prevent small vibrations of the crescent  4 . 
         [0038]    The shape of the starting portion  13   a  of the outlet port  13  is the shape for which the time at which the outer cell  5  starts to link with the outlet port  13  and the time at which the inner cell  6  starts to link with the outlet port  13  are simultaneous (including approximately simultaneously), as stated previously. Specifically, as shown in  FIG. 1B  and  FIG. 2 , in the starting portion  13   a  of the outlet port  13 , a port projection portion  131  is formed in which the outer periphery side of the outlet port  13  projects along the circumferential direction. 
         [0039]    In other words, the part at the starting portion  13   a  of the outlet port  13  and near the inner peripheral side surface  11   a  of the rotor chamber  11  is formed projecting towards the finishing portion  12   b  of the inlet port  12  along the circumferential direction. The port projection portion  131  has a path width that is approximately half the port width (the direction along the diametral direction of the rotor chamber  11 ) at the starting portion  13   a  of the outlet port  13 . 
         [0040]    Also, in the starting portion  13   a,  the portion in which the port projection portion  131  is not formed is referred to as the non-projecting starting edge  132 . The port projection portion  131  is the area where the tooth top portions  21  of the outer rotor  2  pass, and the non-projecting starting edge  132  is the area where the tooth top portions  31  of the inner rotor  3  pass. 
         [0041]    The projection length T of the port projection portion  131  from the non-projecting starting edge  132  is set so that the time at which the tooth top portion  31  of the inner rotor  3  starts to separate from the arc-shaped concave surface side  42  of the crescent  4  and the inner cell  6  starts to link with the non-projecting starting edge  132 , and the time at which the tooth top portion  21  of the outer rotor  2  starts to separate from the arc-shaped convex surface side  41  of the crescent  4  and the outer cell  5  starts to link with the port projection portion  131  is simultaneous (see  FIG. 2 ). 
         [0042]    Furthermore, the shape of the continuity area K, which is the portion that connects the port projection portion  131  and the non-projecting starting edge  132  of the outlet port  13  in the circumferential direction, is formed so that its shape approximately coincides with the shape of the arc-shaped convex surface side  41  of the crescent  4  on the side near its other end (see  FIG. 2 ). In other words, the continuity area K is formed in an approximate arc-shape that is similar to the outer peripheral shape of the arc-shaped convex surface side  41  of the crescent  4  near the outlet port  13  end. In this way, when the outer cells  5  link with the outlet port  13 , the fluid in the outer cells  5  can smoothly flow into the outlet port  13 .