Abstract:
The present invention provides a brushless motor for a fluid pump that allows implementing a fluid pump that overcomes problems of durability and reduction of energy efficiency due to DC motors in the related art and provides excellent operational characteristics, by ensuring a space allowing fluid to flow between a stator and a rotor, and ensuring and maintaining excellent driving characteristics of a motor, and a fluid pump using the brushless motor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a brushless motor, in more detail, a structure of a brushless motor that is used in a fluid pump pumping and discharging fluid, and a fluid pump using the brushless motor. 
         [0003]    2. Description of the Related Art 
         [0004]    In fluid pumps pumping and discharging fluid, fuel pumps that are mounted in a fuel tank of vehicles and pump fuel have been known, and typical DC motors equipped with a common commutator have been used in the fuel pumps in the related art. 
         [0005]    The DC motors are configured to be supplied with needed electricity for driving a commutator and a brush, in which the durability has a basic problem due to loose contact by wear of the brush and the method of supplying electricity by using contact of the commutator and the brush consumes a large amount of electric power in operation by reducing the efficiency of the DC motors, thereby reducing energy efficiency. 
         [0006]    Brushless motors has been proposed to overcome the defects of the DC motors and an interior permanent magnet brushless motor generally has a small gap between a stator and a rotor because the small gap between the stator and the rotor is advantageous in driving the motor, which is inadequate to a fluid pump that should pump and flow fuel between a stator and a rotor. 
       SUMMARY OF THE INVENTION 
       [0007]    It is an object of the present invention to provide a brushless motor for a fluid pump that allows implementing a fluid pump that overcomes problems of durability and reduction of energy efficiency due to DC motors in the related art and provides excellent operational characteristics, by ensuring a space allowing fluid to flow between a stator and a rotor, and ensuring and maintaining excellent driving characteristics of a motor, and a fluid pump using the brushless motor. 
         [0008]    A brushless motor for a fluid pump according to an embodiment of the present invention includes: a stator core having a cross section in which six core shoes symmetrically protrude toward the center of a circle and six slots for winding are formed between the core shoes; in which two core shoe grooves recessed in the longitudinal direction of the stator core the inner side of each of the core shoes are each formed with a center on a core shoe groove center line spaced apart at 8.4°±1° from a straight line passing through the center of the core shoe from the center of the stator core, and the width and depth of the core shoe grooves are 1.5 mm±0.5 mm and 0.53 mm±0.1 mm, respectively; a rotor core, which is inserted in the stator core, has rectangular permanent magnet holes that are formed in the circumferential direction from the center of the rotor core to be filled with four permanent magnets; symmetric bridge holes are formed at both ends of the permanent magnet hole; the bridge hole has a first wall that is spaced apart at 14.7°±2° from a straight line passing through the center of two adjacent permanent magnet holes from the center of the rotor core, a second wall that is connected to the first wall and spaced inside while maintaining a uniform thickness of 0.6 mm±0.1 mm from the outer circumference of the rotor core, a third wall that is connected to the second wall and spaced apart at 0.3 mm±0.1 mm from and in parallel with a straight line passing through the center of two adjacent permanent magnet holes from the center of the rotor core, and a fourth wall that is connected with the first wall and spaced apart at 0.35 mm±0.1 mm from and in parallel with a wall, which is closer to the center of the rotor core, of the permanent magnet hole; and the length of the fourth wall forming the bridge hole is set to 0.41 mm±0.1 mm. 
         [0009]    The first wall to the fourth wall forming the bridge hole are connected in the order of the fourth wall—the first wall—the second wall—the third wall, and the portion between the fourth wall and the third wall may be communicated with the permanent magnet hole. 
         [0010]    A fluid pump using a brushless motor according to the present invention includes: the brushless motor; a cover in which the brushless motor is disposed; a connector that is disposed to seal one side of the cover, has a terminal for supplying electricity to the brushless motor, and is equipped with a check valve discharging pumped fluid; a spring buffer that elastically supports a rotary shaft of the brushless motor against the connector; a lower casing that is disposed to seal the other side of the cover; an upper casing that is disposed above the lower casing; and an impeller that is disposed between the lower casing and the upper casing and pumps fluid by using rotational force transmitted from the rotary shaft of the brushless motor. 
         [0011]    The spring buffer may be composed of a coil spring inserted in a spring-seating groove formed in the connector and a pressing member formed to transmit the elastic force of the coil spring to one end of the rotary shaft of the brushless motor. 
         [0012]    The present invention provides a brushless motor for a fluid pump that allows implementing a fluid pump that overcomes problems of durability and reduction of energy efficiency due to DC motors in the related art and provides excellent operational characteristics, by ensuring a space allowing fluid to flow between a stator and a rotor, and ensuring and maintaining excellent driving characteristics of a motor, and a fluid pump using the brushless motor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a cross-sectional view illustrating the structure of a fluid pump using a brushless motor according to the present invention; 
           [0014]      FIG. 2  is a view illustrating the cross-sectional shape of a stator core used in the brushless motor of  FIG. 1 ; 
           [0015]      FIG. 3  is a view illustrating in detail the main parts of the stator core of  FIG. 2 ; 
           [0016]      FIG. 4  is a view illustrating the cross-sectional shape of a rotor core used in the brushless motor of  FIG. 1 ; 
           [0017]      FIG. 5  is a view illustrating in detail the main parts of the rotor core of  FIG. 4 ; 
           [0018]      FIGS. 6 and 7  are graphs comparing and showing test results for a model according to the related art, a first modified model, and a model according to the present invention; 
           [0019]      FIG. 8  is a detailed view of a graph about cogging torque of the model according to the related art of  FIG. 6 ; 
           [0020]      FIG. 9  is a detailed view of a graph about an operational torque of the model according to the related art of  FIG. 6 ; 
           [0021]      FIG. 10  is a detailed view of a graph about counter electromotive force of the model according to the related art of  FIG. 6 ; 
           [0022]      FIG. 11  is a detailed view of a graph about cogging torque of the first modified model of  FIG. 6 ; 
           [0023]      FIG. 12  is a detailed view of a graph about an operational torque of the first modified model of  FIG. 6 ; 
           [0024]      FIG. 13  is a detailed view of a graph about counter electromotive force of the first modified model of  FIG. 6 ; 
           [0025]      FIG. 14  is a detailed view of a graph about cogging torque of the model according to the present invention of  FIG. 6 ; 
           [0026]      FIG. 15  is a detailed view of a graph about an operational torque of the model according to the present invention of  FIG. 6 ; and 
           [0027]      FIG. 16  is a detailed view of a graph about counter electromotive force of the model according to the present invention of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Referring to  FIGS. 1 to 5 , a brushless motor according to an embodiment of the present invention includes a stator core  5  having a cross section in which six core shoes  1  symmetrically protrude toward the center of a circle and six slots  3  for winding are formed between the core shoes  1 , and two core shoe grooves  7  recessed in the longitudinal direction of the stator core  5  are formed on the inner side of each of the core shoes  1 . 
         [0029]    The two core shoe grooves  7  are each formed with a center on a core shoe groove center line B spaced apart at 8.4° from a straight line A passing through the center of the core shoe  1  from the center of the stator core  5 , and the width and depth of the core shoe grooves  7  are 1.5 mm and 0.53 mm, respectively. 
         [0030]    A rotor core  9 , which is inserted in the stator core  5 , has permanent magnet holes  11  that are formed in the circumferential direction from the center of the rotor core  9  to be filled with four permanent magnets. Further, bridge holes  13  are symmetrically formed from the center portion of the permanent magnet hole  11  at both ends of the permanent magnet hole  11 . 
         [0031]    The permanent magnet hole  11  is formed in a rectangular shape, and the bridge hole  13  has a first wall  15  that is spaced apart at 14.7° from a straight line C passing through the center of two adjacent permanent magnet holes  11  from the center of the rotor core  9 , a second wall  17  that is connected to the first wall  15  and spaced inside while maintaining a uniform thickness of 0.6 mm from the outer circumference of the rotor core  9 , a third wall  19  that is connected to the second wall  17  and spaced apart at 0.3 mm from and in parallel with a straight line C passing through the center of two adjacent permanent magnet holes  11  from the center of the rotor core  9 , and a fourth wall  21  that is connected with the first wall  15  and spaced apart at 0.35 mm from and in parallel with a wall W, which is closer to the center of the rotor core, of the permanent magnet hole  11 , in which the length of the fourth wall  21  forming the bridge hole  13  is set to 0.41 mm. 
         [0032]    The first wall  15  to the fourth wall  21  forming the bridge hole  13  are connected in the order of the fourth wall  21 —the first wall  15 —the second wall  17 —the third wall  19 , and the portion between the fourth wall  21  and the third wall  19  is communicated with the permanent magnet hole  11 . 
         [0033]    On the other hand, an embodiment of a fluid pump using a brushless motor according to the present invention is configured to include: a brushless motor  23  having the above structure; a cover  25  in which the brushless motor  23  is disposed; a connector  31  that is disposed to seal one side of the cover  25 , has a terminal  27  for supplying electricity to the brushless motor  23 , and is equipped with a check valve  29  discharging pumped fluid; a spring buffer  33  that elastically supports a rotary shaft  39  of the brushless motor  23  against the connector  31 ; a lower casing  35  that is disposed to seal the other side of the cover  25 ; an upper casing  37  that is disposed above the lower casing  35 ; and an impeller  41  that is disposed between the lower casing  35  and the upper casing  37  and pumps fluid by using rotational force transmitted from the rotary shaft  39  of the brushless motor  23 . 
         [0034]    For reference, the fluid pump of this embodiment is used as a fuel pump that is mounted in the fuel tank of a vehicle. 
         [0035]    The spring buffer  33  is composed of a coil spring  45  inserted in a spring-seating groove  43  formed in the connector  31  and a pressing member  47  formed to transmit the elastic force of the coil spring  45  to one end of the rotary shaft  39  of the brushless motor  23 . 
         [0036]    The lower casing  35  has an inlet  49  for sucking fluid, such as fuel, and though not clearly shown in the figures, the upper casing  37  has an outlet allowing the impeller  41  to discharge the pumped fluid while rotating. 
         [0037]    Accordingly, the fluid discharged through the outlet is stored in a space between the upper casing  37  and the brushless motor  23 , flows to the connector  31  through a space between the stator and the rotor of the brushless motor  23 , and then is discharged outside through the check valve  29  of the connector  31 . 
         [0038]    In particular, in the present invention, since the fluid flows through the core shoe grooves  7  when passing through between the stator and the rotor, it is possible to overcome the problem in that sufficient channel is not formed in brushless motors in the related art, such that the fluid can smoothly flow. 
         [0039]    Further, the core shoe grooves  7  reduce cogging torque that causes cogging in which the rotor cannot smoothly rotate and rotates while chattering by the relationship between the magnetic field of the permanent magnets of the rotor and the magnetic field formed by the stator core  5  such that the rotor can smoothly rotate. 
         [0040]    Meanwhile, the spring buffer  33  allows the stator to stably and smoothly rotate by stably supporting the rotor that is axially moved by pressure change generated in the space between the upper casing  37  and the brushless motor  23  when pumping the fluid as described above. 
         [0041]    Further, the detailed structures of the bridge holes  13  of the rotor core  9  increases efficiency of the brushless motor  23  and improves the counter electromotive force waveform for easily controlling the brushless motor  23  without using a sensor. 
         [0042]    That is, in controlling electric current that is supplied to stator wires of the brushless motor  23  without using a specific sensor, the control can be more easily achieved by making the counter electromotive force waveform outputted to the wires of the stator in a smooth curve shape without excessive changes. 
         [0043]      FIGS. 6 and 7  show test results for a model of simple brushless motors in the related art, a first modified model manufactured by additionally forming core shoe grooves to the model according to the related art, and a model of the present invention manufactured by changing the shape of the bridge holes in the first modified model, in which the waveforms of cogging torque, operational torque, and counter electromotive force are compared and shown for each model. For reference,  FIGS. 8 to 16  show detailed views of graphs used in  FIGS. 6 and 7 . 
         [0044]    Comparing first the cogging torque with the operational torque, when core shoe grooves are formed as in the first modified model, the magnitudes of cogging torque and torque ripple are considerably decreased as compared with the model according to the related art; however, ripple is generated in the cogging torque and the torque waveform of the operational torque is distorted, such that the motor may make vibration and noise. 
         [0045]    Therefore, when the shape of bridge holes are additionally changed as in the model according to the present invention, as shown in the figures, the cogging torque becomes larger than the first modified model, but smaller than the model according to the related art and a smooth waveform without ripple is achieved. Further, the magnitude of operational torque largely increases as compared with the model according to the related art, and the torque ripple is larger than the first modified model, but is significantly reduced as compared with the model according to the related art, such that it is possible to ensure overall excellent characteristics of the motor. 
         [0046]    Further, comparing the state of the counter electromotive force for controlling the electric current that is applied to the stator wires without using a sensor with reference to  FIG. 7 , the counter electromotive force is largest and ideal waveform is obtained in the model according to the related art; however, large cogging torque and torque ripple are generated as described above, such that it is not preferable in terms of overall characteristics of the motor. Further, when a change is applied as in the first modified model for improving the cogging torque and the torque ripple, as shown in the figure, the waveform of the counter electromotive force is distorted sharp and control becomes difficult. Accordingly, when the configuration is changed as in the model according to the present invention, as shown in the figure, a smooth waveform without deformation is formed, though not better than the model according to the related art, such that easier characteristics are provided for the control. 
         [0047]    As a result, the model according to the present invention is a model that is provided with various characteristics appropriately optimized, including the cogging torque, operational torque, and counter electromotive force, such that it is possible to provide characteristics of a motor that can be easily controlled, operates stably without noise, generates relatively large operational torque, and has excellent durability.