Patent Publication Number: US-2022235763-A1

Title: Gear pump or motor

Description:
TECHNICAL FIELD 
     The present invention relates to a motor or a gear pump including a hydraulic gear pump. The motor or the gear pump is used for power conversion in various apparatuses. 
     BACKGROUND ART 
     A hydraulic gear pump includes: a pair of spur gears housed in a hollow space provided in a body with the spur gears meshing with each other; a driving axle and a driven axle of the respective spur gears; a suction passage for supplying hydraulic oil as working liquid provided in a low-pressure area in which the spur gears separate; and a discharge passage for discharging the hydraulic oil from the hollow space provided in a high-pressure area in which the spur gears mesh (see Patent literature 1). 
     Furthermore, a hydraulic helical gear pump that uses helical gears in place of spur gears has also been proposed (see Patent Literature 2). The helical gears are characterized by quietness and continuous tooth contact without containment. 
       FIG. 14  is a sectional side view around a body  11  of a traditional hydraulic gear pump in which spur gears are used. 
     In the hydraulic gear pump, a pair of spur gears  23  and  24  that mesh with each other are housed in a hollow space  19  provided in the body  11  which is called a spectacle-shaped hole. The spur gear  23  is fixed to a driving axle  21  rotated by a motor which is not shown. The spur gear  24  is fixed to a driven axle  22 . The spur gears  23  and  24 , meshing with each other, are rotated by the driving axle  21  in the respective directions indicated by the arrows in  FIG. 14 . 
     In the low-pressure area where teeth of the paired spur gears  23  and  24  in the hollow space  19  provided in the body  11  separate from each other, a suction passage  31  is formed for supplying hydraulic oil to the hollow space  19 . In the high-pressure area where teeth of the paired spur gears  23  and  24  in the hollow space  19  provided in the body  11  mesh, a discharge passage  33  is formed for discharging hydraulic oil from the hollow space  19 . 
       FIG. 15  is a sectional view taken along line B-B in  FIG. 14 , and shows the suction passage  31  viewed from the hollow space  19  and outside of the body  11 . 
     As shown in  FIG. 15 , the suction passage  31  has a circular cross section. The discharge passage  33  also has a circular cross section, like the suction passage  31 . 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2008-163759 A 
         Patent Literature 2: WO 2014/141377 A 
       
    
     If the capacity of the hydraulic gear pump is to be increased, the flow rate of the hydraulic oil sucked by the pump is also increased. Thus, it is necessary to prepare the suction passage  31  with a large scale. However, the opening of the large-scaled suction passage  31  interferes with the outskirt of the low-pressure area in the hollow space  19 , since the cross section of the suction passage  31  has a circular shape as mentioned earlier. The areas L shown in  FIG. 14  serve as sealing areas for preventing hydraulic oil from leaking from the high-pressure area toward the low-pressure area, owing to the sealing effect between the inner peripheral face of the hollow space  19  and tooth tips of the spur gears  23  and  24 . Accordingly, if the cross sectional area of the suction passage  31  is increased, the opening of the suction passage  31  interferes with the sealing area L. This prevents the sealing area L from adequately functioning. If the sealing area L is reduced, the pump volumetric efficiency, defined as a ratio between an actual discharge amount by the hydraulic gear pump and its theoretical discharge amount, deteriorates. 
     Meanwhile, if, despite an increase in the capacity of the pump, the suction passage  31  is not enlarged, the flow velocity of the hydraulic oil should increase due to the small opening area of the suction passage. This causes the generation of cavitation. 
     The present invention is made for solving the aforementioned problems. An object of the present invention is to provide a gear pump or a motor, in which the sealing area is adequately secured and the pump volumetric efficiency is maintained even if the cross sectional area of the flow-in passage is increased, to thereby supply a hydraulic liquid in a preferable manner. 
     SUMMARY OF INVENTION 
     The invention of claim  1  includes: a pair of gears housed in a hollow space provided in a body, in a state where the gears mesh with each other; a suction passage for supplying a hydraulic liquid to the hollow space; and a discharge passage for discharging the hydraulic liquid from the hollow space. The suction passage has an opening with respect to the hollow space, and the dimension of the opening in the direction along the tooth width of the gear is larger than the dimension of the opening in the direction perpendicular to the direction along the tooth width of the gear. 
     In the invention of claim  2  according to claim  1 , the dimension of the opening, of the suction passage, with respect to the hollow space in the direction along the tooth width of the gear is larger than the dimension, in the direction along the tooth width of the gear, of the opening of the suction passage in the side from which the hydraulic liquid is supplied, and the dimension of the opening, of the suction passage, with respect to the hollow space in the direction perpendicular to the direction along the tooth width of the gear is smaller than the dimension, in the direction perpendicular to the direction along the tooth width of the gear, of the opening of the suction passage in the side from which the hydraulic liquid is supplied. 
     In the invention of claim  3  according to claim  2 , the opening of the suction passage in the side from which the hydraulic liquid is supplied is shaped in a circle, the dimension of the opening of the suction passage with respect to the hollow space in the direction along the tooth width of the gear is larger than the diameter of the circle, and the dimension of the opening, of the suction passage, with respect to the hollow space in the direction perpendicular to the direction along the tooth width of the gear is smaller than the diameter of the circle. 
     In the invention of claim  4  according to any one of claims  1  to  3 , the cross sectional area of the suction passage is constant from the opening in the side from which the hydraulic liquid is supplied to the opening with respect to the hollow space. 
     In the invention of claim  5  according to any one of claims  1  to  4 , the gear is a spur gear, and the opening of the suction passage with respect to the hollow space has opposite ends with respect to the direction perpendicular to the direction along the tooth width of the spur gear parallel to the tooth tip line of the spur gear in an area, of the opening, which faces the spur gear. 
     In the invention of claim  6  according to any one of claims  1  to  4 , the gear is a helical gear, and the dimension of the opening, of the suction passage, with respect to the hollow space in the direction perpendicular to the direction along the tooth width of the helical gear is larger in the side where helical gears which are paired and mesh with each other separate earlier and smaller in the side where the paired helical gears meshing with each other separate later, in an area, of the opening, which faces the helical gears. 
     In the invention of claim  7  according to claim  6 , the opening of the suction passage with respect to the hollow space has opposite ends in the direction perpendicular to the direction along the tooth width of the helical gears, and each of the opposite ends is shaped in a sine curve corresponding to the tooth tip line of the helical gears, in the area of the opening, which faces the helical gears. 
     The invention of claim  8  includes: a pair of helical gears housed in a hollow space provided in a body, in a state where the helical gears mesh with each other; a suction passage for supplying a hydraulic liquid to the hollow space; and a discharge passage for discharging the hydraulic liquid from the hollow space. The opening of the suction passage with respect to the hollow space has a dimension in the direction perpendicular to the direction along the tooth width of the helical gears. The dimension is larger in the side where the helical gears that are paired and mesh with each other separate earlier and smaller in the side where the paired helical gears meshing with each other separate later, in the area, of the opening, which faces the helical gears. 
     In the invention of claim  9  according to claim  8 , the opening of the suction passage with respect to the hollow space has opposite ends in the direction perpendicular to the direction along the tooth width of the helical gears shaped in a sine curve corresponding to the tooth tip line of the helical gears, in the area of the opening, which faces the helical gears. 
     According to the invention of claim  1 , the cross sectional area of the suction passage can be increased while the sealing area between the inner peripheral face of the hollow space and the tooth tips of the gear is secured. Accordingly, it is possible to prevent the pump volumetric efficiency from deteriorating due to reduction in the flow rate of the hydraulic liquid. In addition, it is possible to prevent cavitation by controlling the occurrence of defective suction, to thereby enable a prolonged product life. 
     According to the invention of claim  2 , the dimension of the opening in the direction along the tooth width of the gear is increased while the cross sectional area of the suction passage is kept constant. This can reduce the dimension of the opening in the direction perpendicular to the direction along the tooth width of the spur gear. Therefore, it is possible to efficiently increase the cross sectional area of the suction passage, while the sealing area between the inner peripheral face of the hollow space and the tooth tips of the spur gear is secured. 
     According to the invention of claim  3 , the suction passage can be connected to a hydraulic-liquid supply tube or the like, using a commonly-used apparatus. 
     According to the invention of claim  4 , the hydraulic liquid can be smoothly supplied from the suction passage to the hollow space. 
     According to the invention of claim  5 , when spur gears are used as the paired gears, it is possible to efficiently increase the cross sectional area of the suction passage while the sealing area between the inner peripheral face of the hollow space and the tooth tips of the gear is secured. 
     According to the inventions of claims  6  to  9 , when helical gears are used as the paired gears, it is possible to further efficiently increase the cross sectional area of the suction passage while the sealing area between the inner peripheral face of the hollow space and the tooth tips of the gear is secured. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal sectional view of a gear pump according to the first embodiment of the present invention. 
         FIG. 2  is a cross sectional view of the gear pump, taken along line A-A in  FIG. 1 . 
         FIG. 3  is a cross sectional view taken along line B-B in  FIG. 2 , and shows a suction passage  32  viewed from a hollow space  19  and the outside of a body  11 . 
         FIG. 4  is an explanation view indicating a shape of the suction passage  32  in a side close to the hollow space  19  in the body  11 . 
         FIG. 5  is a cross sectional view taken along the line B-B in  FIG. 2 , and shows the suction passage  32  viewed from the hollow space  19  and the outside of the body  11  according to a first modification of the first embodiment of the present invention. 
         FIG. 6  is an explanation view indicating a shape of the suction passage  32  in a side close to the hollow space  19  in the body  11 , according to the first modification of the first embodiment of the present invention. 
         FIG. 7  is an explanation view indicating a shape of the suction passage  32  in the side close to the hollow space  19  in the body  11 , according to a second modification of the first embodiment of the present invention. 
         FIG. 8  is a longitudinal sectional view of a gear pump according to the second embodiment of the present invention. 
         FIG. 9  is a cross sectional view of the gear pump, taken along line A-A in  FIG. 8 . 
         FIG. 10  is a cross sectional view taken along line B-B in  FIG. 9 , and shows the suction passage  32  viewed from the hollow space  19  and the outside of the body  11 . 
         FIG. 11  is an explanation view indicating a shape of the suction passage  32  in the side close to the hollow space  19  in the body  11 . 
         FIG. 12  is an explanation view indicating a shape of the suction passage  32  in the side close to the hollow space  19  in the body  11 , according to a modification of the second embodiment of the present invention. 
         FIG. 13  is an explanation view indicating a shape of the suction passage  32  in the side close to the hollow space  19  in the body  11 , according to another modification of the second embodiment of the present invention. 
         FIG. 14  is a sectional side view around a body  11  of a traditional gear pump. 
         FIG. 15  is a cross sectional view taken along line B-B in  FIG. 14 , and shows the suction passage  31  viewed from the hollow space  19  and the outside of the body  11 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention are described, with reference to the drawings.  FIG. 1  is a longitudinal sectional view of a gear pump according to the first embodiment of the present invention, and  FIG. 2  is a cross sectional view of the gear pump taken along line A-A in  FIG. 1 . 
     The gear pump uses hydraulic oil as a hydraulic liquid, and serves as a hydraulic gear pump for sending the hydraulic oil by the operation of a pair of spur gears  23  and  24 . The gear pump includes a body  11  held between a front cover  12  and a rear cover  13  via a gasket  14 , and a pair of the spur gears  23  and  24  that mesh with each other and are housed in a hollow space  19  that is provided in the body  11  and is called as a spectacle-shaped hole. The spur gear  23  is fixed to a driving axle  21  that is rotated by a motor which is not shown. The spur gear  24  is fixed to a driven axle  22 . Each of the driving axle  21  and the driven axle  22  has one end pivotally supported, via a bush  15 , by a bearing hole  17  provided in the front cover  12 , and the other end pivotally supported, via a bush  16 , by a bearing hole  18  provided in the rear cover  13 . The spur gears  23  and  24 , meshing with each other, are individually rotated by the driving axle  21  in the direction indicated by the arrows in  FIG. 2 . 
     In a low-pressure area in the hollow space  19  provided in the body  11 , where teeth of each of the paired spur gears  23  and  24  separate from each other, a suction passage  32  for supplying the hydraulic oil to the hollow space  19  is formed. In a high-pressure area in the hollow space  19  provided in the body  11 , where teeth of each of the paired spur gears  23  and  24  mesh with each other, a discharge passage  33  for discharging the hydraulic oil from the hollow space  19  is formed. It should be noted that the discharge passage  33  may be formed to extend in an X direction that is the direction along the axle center of each of the driving axle  21  and the driven axle  22  (a direction perpendicular to the sheet of  FIG. 2 ). 
       FIG. 3  is a cross sectional view taken along line B-B in  FIG. 2 , and shows the suction passage  32  viewed from the hollow space  19  (right side in  FIG. 2 ) and the outside of the body  11  (left side in  FIG. 2 ).  FIG. 4  is an explanation view showing a shape of the suction passage  32  in a side close to the hollow space  19  in the body  11 . The arrow T in  FIG. 4  shows an area of the suction passage  32 , which faces the spur gears  23  and  24 . 
     As shown in these drawings, the cross section of the suction passage  32  has a rectangular shape viewed from the hollow space  19  side in the body  11 , and has a circular shape viewed from the outside of the body  11  (a side from which the hydraulic oil is supplied). The suction passage  32  has a shape in which the rectangular shape in the hollow space  19  side in the body is smoothly connected with the circular shape in the outside of the body  11 . As aforementioned, the shape of the suction passage  32  in the side from which the hydraulic oil is supplied is a circle, so that a commonly-used apparatus can be used when the suction passage  32  is connected to a supply tube or the like for supplying the hydraulic oil. 
     Regarding the rectangular shape of the suction passage  32  in the hollow space  19  side in the body  11 , a dimension in a direction along the tooth width of the spur gears  23  and  24  (X direction) is larger than a dimension in a direction perpendicular to the direction along the tooth width of the spur gears  23  and  24  (Y direction). In other words, a long side of the rectangular extends in the direction along the tooth width of the spur gears  23  and  24 , and a short side extends in the direction perpendicular to the tooth width direction. 
     Regarding the rectangular shape of the suction passage  32  in the hollow space  19  side in the body  11 , the dimension in the direction along the tooth width of the spur gears  23  and  24  (the direction along the long side of the rectangular shape) is larger than the diameter of the opening of the suction passage  32  in the outside of the body  11 , and a dimension in the direction perpendicular to the direction along the tooth width of the spur gears  23  and  24  (the direction along the short side of the rectangular shape) is smaller than the diameter of the opening of the suction passage  32  in the outside of the body  11 . 
     The cross sectional area of the suction passage  32  from its opening in the outside of the body  11  (the side from which the hydraulic oil is supplied) to its opening with respect to the hollow space  19  is substantially constant. 
     The suction passage  32  has such a shape, to thereby increase its cross sectional area while adequately securing the sealing area L, which is shown in  FIG. 2 , between the inner peripheral face of the hollow space  19  and the tooth tips of the spur gears  23  and  24 . Accordingly, it is possible to prevent the pump volumetric efficiency from deteriorating due to the reduction in flow rate of the hydraulic oil. In addition, it is possible to prevent the occurrence of defective suction, to thereby enable a prolonged product life. 
     The dimension, in the direction along the tooth width of the spur gears  23  and  24 , of the opening of the suction passage  32  with respect to the hollow space  19  is increased, while the cross sectional area of the suction passage  32  is kept constant. This reduces the dimension, in the direction perpendicular to the tooth width direction, of the opening of the suction passage  32  with respect to the hollow space  19 . Therefore, it is possible to efficiently enable the cross sectional area of the suction passage  32  to be increased while the sealing area L between the inner peripheral face of the hollow space  19  and the tooth tips of the spur gears  23  and  24  is secured. 
     In addition, the cross sectional area of the suction passage  32  from its opening in the side from which the hydraulic oil is supplied to its opening with respect to the hollow space  19  is substantially constant, thereby allowing the hydraulic oil to be smoothly supplied from the suction passage  32  to the hollow space  19 . 
     In the aforementioned embodiment, the suction passage  32  has a shape in which the rectangular shape in the hollow space  19  side in the body  11  is smoothly connected with the circular shape in the outside of the body  11 . Here, the suction passage  32  may have a shape in which the rectangular shape is stepwise connected with the circle. Alternatively, the suction passage  32  may have shapes other than the shape in which the rectangular shape is connected with the circle. 
       FIG. 5  is a cross sectional view taken along line B-B in  FIG. 2 , according to a first modification of the first embodiment of the present invention, and shows the suction passage  32  viewed from the hollow space  19  and the outside of the body  11 .  FIG. 6  is an explanation view indicating a shape of the suction passage  32  in a side close to the hollow space  19  in the body  11 , according to the first modification of the first embodiment of the present invention. 
     The suction passage  32  in the hollow space  19  side in the body  11  has a rectangular shape in the aforementioned first embodiment, whereas the suction passage  32  in the hollow space  19  side in the body  11  has an oval shape in this first modification. Other configurations are the same as those in the first embodiment. 
     If such a configuration is adopted, the shape of the suction passage  32  in the hollow space  19  side in the body  11  is close to the rectangular shape shown in  FIG. 4 , in an area that is indicated by the arrow T in  FIG. 6  and faces the spur gears  23  and  24 . Therefore, an effect close to those obtained in the embodiment shown in  FIGS. 3 and 4  can be obtained. 
       FIG. 7  is an explanation view indicating a shape of the suction passage  32  in the side close to the hollow space  19  in the body  11 , according to a second modification of the first embodiment of the present invention. 
     The suction passage  32  in the hollow space  19  side in the body  11  has the rectangular shape in the embodiment shown in  FIG. 4 , and the suction passage  32  in the hollow space  19  side in the body  11  has the oval shape in the first modification shown in  FIG. 6 . In this instance, in the second modification, the suction passage  32  in the hollow space  19  side in the body  11  has a shape in which a rectangular shape and a circular shape are combined. Other configurations are the same as those in the first embodiment. 
     If such a configuration is adopted, the shape of the suction passage  32  in the hollow space  19  side in the body  11  is similar to the rectangular shown in  FIG. 4  in the area that is indicated by the arrow T in  FIG. 6  and faces the spur gears  23  and  24 . Therefore, an effect similar to those obtained in the embodiment shown in  FIGS. 3 and 4  can be obtained. 
     Subsequently, another embodiment of the present invention is described.  FIG. 8  is a longitudinal sectional view of a gear pump according to the second embodiment of the present invention.  FIG. 9  is a cross sectional view of the gear pump taken along line A-A in  FIG. 8 . 
     The gear pump uses hydraulic oil as the hydraulic liquid, and serves as a hydraulic gear pump for sending the hydraulic oil by operation of a pair of helical gears  25  and  26 . The gear pump includes the body  11  held between the front cover  12  and the rear cover  13 , a pair of the helical gears  25  and  26  that mesh with each other and are housed in the hollow space  19  that is provided in the body  11  and is called a spectacle-shaped hole, and side plates  27  and  28  that hold a pair of the helical gears  25 ,  26  in the hollow space  19 . The helical gear  25  is fixed to the driving axle  21  that is rotated by a motor which is not shown. The helical gear  26  is fixed to the driven axle  22 . Each of the driving axle  21  and the driven axle  22  has one end pivotally supported, via the bush  15 , by the bearing hole  17  provided in the side plate  27 , and the other end pivotally supported, via the bush  16 , by the bearing hole  18  provided in the side plate  28 . The helical gears  25  and  26 , meshing with each other, are individually rotated by the driving axle  21  in the directions indicated by the arrows in  FIG. 9 . 
     In a low-pressure area in the hollow space  19  provided in the body  11 , where teeth of each of the paired helical gears  25  and  26  separate from each other, the suction passage  32  for supplying the hydraulic oil to the hollow space  19  is formed. In a high-pressure area in the hollow space  19  provided in the body  11 , where teeth of each of the paired helical gears  25  and  26  mesh with each other, the discharge passage  33  for discharging the hydraulic oil from the hollow space  19  is formed. It should be noted that the discharge passage  33  may be formed to extend in the X direction that is the direction along the axle center of each of the driving axle  21  and the driven axle  22  (a direction perpendicular to the sheet of  FIG. 9 ). 
       FIG. 10  is a cross sectional view taken along line B-B in  FIG. 9 , and shows the suction passage  32  viewed from the hollow space  19  (right side in  FIG. 9 ) and the outside of the body  11  (left side in  FIG. 9 ).  FIG. 11  is an explanation view showing a shape of the suction passage  32  in a side close to the hollow space  19  in the body  11 . The arrow T in  FIG. 11  shows an area of the suction passage  32 , which faces the helical gears  25  and  26 . 
     As shown in  FIG. 11 , the cross section of the suction passage  32 , in the hollow space  19  side in the body  11 , is shaped as an opening having two sides that are opposite to each other and shaped in sine curves  39  with a shape corresponding to the tooth tip line of each of the helical gears  25  and  26 , and the other two sides which are opposite to each other and shaped in straight lines. The opening is shaped such that in the area T that faces the helical gears  25  and  26 , a dimension in a direction perpendicular to the direction along the tooth width of the helical gears  25  and  26  (Y direction shown in  FIGS. 8, 9, and 10 , and the vertical direction in  FIG. 11 ) is larger in a side where the paired and meshed helical gears  25  and  26  separate from each other earlier in one tooth line, and is smaller in a side where the paired and meshed helical gears  25  and  26  separate from each other later in one tooth line. The cross section of the suction passage  32  has a circular shape in the outside of the body  11  (a side from which the hydraulic oil is supplied). The suction passage  32  has a shape in which the opening shape in the hollow space  19  side in the body  11  is smoothly connected with the circular shape in the outside of the body  11 . As aforementioned, the shape of the suction passage  32  in the side from which the hydraulic oil is supplied is a circle, so that a commonly-used apparatus can be used when the suction passage  32  is connected to a supply tube or the like for supplying the hydraulic oil. 
     Regarding the opening of the suction passage  32  in the side close to the hollow space  19  in the body  11 , a dimension in a direction along the tooth width of the helical gears  25  and  26  (X direction) is larger than a dimension in a direction perpendicular to the tooth width of the helical gears  25  and  26  (Y direction). 
     Regarding the opening of the suction passage  32  in the side close to the hollow space  19  in the body  11 , the dimension in the direction along the tooth width of the helical gears  25  and  26  is larger than the diameter of the opening of the suction passage  32  in the outside of the body  11 , and the dimension in the direction perpendicular to the direction along the tooth width of the helical gears  25  and  26  is smaller than the diameter of the opening of the suction passage  32  in the outside of the body  11 . 
     The cross sectional area of the suction passage  32  from its opening part in the outside of the body  11  (the side from which the hydraulic oil is supplied) to the opening part with respect to the hollow space  19  is substantially constant. 
     The opening of the suction passage  32  has two sides that are the sine curves  39  corresponding to the tooth tip line of the helical gears  25  and  26 , to thereby increase the cross sectional area of the suction passage  32  while adequately securing the sealing area L, which is shown in  FIG. 9 , between the inner peripheral face of the hollow space  19  and the tooth tips of the helical gears  25  and  26 . Accordingly, it is possible to prevent the pump volumetric efficiency from deteriorating due to the reduction in flow rate of the hydraulic oil. In addition, it is possible to prevent the occurrence of defective suction, to thereby enable a prolonged product life. 
     The dimension, in the direction along the tooth width of the helical gears  25  and  26 , of the opening of the suction passage  32  with respect to the hollow space  19  is increased, while the cross sectional area of the suction passage  32  is kept constant. This reduces the dimension, in the direction perpendicular to the tooth width direction, of the opening of the suction passage  32  with respect to the hollow space  19 . Therefore, it is possible to efficiently enable the configuration in which the cross sectional area of the suction passage  32  is increased while the sealing area L between the inner peripheral face of the hollow space  19  and the tooth tips of the helical gears  25  and  26  is secured. 
     The cross sectional area of the suction passage  32  from its opening in the side from which the hydraulic oil is supplied to the opening with respect to the hollow space  19  is substantially constant, thereby allowing the hydraulic oil to be smoothly supplied from the suction passage  32  to the hollow space  19 . 
     The opening, which is shown in  FIG. 11 , of the suction passage  32  in the hollow space  19  side in the body  11  is shaped such that opposite ends of the opening in the direction along the tooth width of the helical gears  25  and  26  define straight lines respectively, in the area that faces the helical gears  25  and  26 . However, the opposite ends of the opening may respectively define curves extending from the area that faces the helical gears  25  and  26  to the outside of the body  11 . 
       FIG. 12  is an explanation view indicating a shape of the suction passage  32  in the side close to the hollow space  19  in the body  11 , according to a modification of the second embodiment of the present invention. 
     The shape of the opening of the suction passage  32  in the hollow space  19  side in the body  11  has two sides shaped in the sine curves  39  each corresponding to the tooth tip line of the helical gears  25  and  26  in the aforementioned second embodiment. Here, the two sides are shaped in straight lines in the modification. Other configurations are the same as those in the second embodiment. 
     If such a configuration is adopted, the shape of the suction passage  32  in the hollow space  19  side in the body  11  is close to the opening shape shown in  FIG. 11 . Therefore, an effect close to those obtained in the embodiment shown in  FIG. 11  can be obtained. 
       FIG. 13  is an explanation view indicating a shape of the suction passage  32  in a side close to the hollow space  19  in the body  11 , according to another modification of the second embodiment of the present invention. 
     The capacity of the gear pump, for example, may cause the tooth tip line of the helical gears  25  and  26  to have a large angle with respect to the direction along the tooth width of the helical gears  25  and  26 . In such a case, the cross sectional area of the suction passage  32  in the hollow space  19  side in the body  11  has two opposite sides that are sine curves  38  each of which has a large angle with respect to the direction along the tooth width of the helical gears  25  and  26 . The sine curves  38  correspond to the tooth tip line of the helical gears  25  and  26 . In this case, in the opening shape of the suction passage  32  in the side close to the hollow space  19  in the body  11 , a dimension in the direction along the tooth width of the helical gears  25  and  26  (X direction) is smaller than a dimension in a direction (Y direction) perpendicular to the direction along the tooth width of the helical gears  25  and  26 , unlike the aforementioned embodiment. 
     However, even in the case where such a configuration is adopted, the two opposite sides of the cross section of the suction passage  32  define the sine curves  38  that correspond to the tooth tip line of each of the helical gears  25  and  26 . Accordingly, the cross sectional shape of the suction passage  32  matches the tooth tip line of the helical gears  25  and  26 , to thereby enable the increase in the cross sectional area of the suction passage for securing a sealing area. 
     In the gear pumps according to the first and second embodiments mentioned earlier, hydraulic oil having pressure higher than that of the discharge passage  33  can be introduced. This takes a rotary torque from the driving axle  21  and allows the gear pump to function as a gear motor exhibiting a motor effect in which an external load is driven, and the hydraulic oil that has a low pressure is discharged from the suction passage  32 . In other words, the gear pump according to each of the embodiments mentioned earlier also serves as a gear motor. 
     Although hydraulic oil is used as the hydraulic liquid in the first and second embodiments mentioned earlier, a hydraulic liquid other than hydraulic oil, such as other liquids, fluids and semiliquids, can be used. 
     REFERENCE SIGNS LIST 
     
         
           11  . . . Body 
           12  . . . Front Cover 
           13  . . . Rear Cover 
           15  . . . Bush 
           16  . . . Bush 
           17  . . . Bearing Hole 
           18  . . . Bearing Hole 
           19  . . . Hollow Space 
           21  . . . Driving Axle 
           22  . . . Driven Axle 
           23  . . . Spur Gear 
           24  . . . Spur Gear 
           25  . . . Helical Gear 
           26  . . . Helical Gear 
           32  . . . Suction Passage 
           33  . . . Discharge Passage 
           38  . . . Sine Curve 
           39  . . . Sine Curve