BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a cooling device for a spindle motor for driving a spindle of a machine tool, and in particular to a cooling device for a built-in-spindle type spindle motor of a machine tool, which can efficiently cool a spindle motor.  
         [0003]     2. Description of the Related Art  
         [0004]     A machine tool such as a numerical control lathe, a machining center, or the like has a spindle motor for rotating a spindle. Such a spindle motor is trending toward a built-in type, in which a spindle motor is integrated with a spindle. A built-in type spindle motor rapidly rotates a spindle without noise and vibration.  
         [0005]     Such a built-in type spindle motor comprises a motor housing  10  as shown in  FIG. 1 . The motor housing  10  is configured to enclose a spindle S. Here, respective bearings  12  are interposed between the motor housing  10  and the spindle S to assist the rotation of the spindle S. In addition, the opposite open sides of the motor housing  10  are sealed by covers  14 .  
         [0006]     The spindle motor comprises a rotor  20  fixed around the spindle S and a stator  22  located to surround the rotor  20  with a clearance t being formed between the rotor  20  and the stator  22 . The stator  22  is secured to the inner circumferential surface of the motor housing  10 .  
         [0007]     The spindle motor is provided with a cooling device for cooling high temperature generated while the spindle motor is being operated. The cooling device is a fluid-type cooling device using fluid such as water or oil, wherein the cooling device comprises a spiral flow passage  30  and fluid supply means for supplying fluid such as water or oil to the spiral flow passage  30 . In particular, the fluid supply means consists of a fluid pump  32 .  
         [0008]     Such a fluid-type cooling device is configured to pump fluid with the fluid pump  32  and then supply the pumped fluid to the spiral flow passage  30 , thereby allowing the fluid passing through the spiral flow passage  30  to cool the motor housing  10 .  
         [0009]     However, such a conventional fluid-type device has a disadvantage in that it can only cool the heat transferred to the motor housing  10  because it employs a construction that supplies cooling fluid to the motor housing  10 .  
         [0010]     Such a disadvantage makes it difficult to cool the rotor  20  and the stator  22 , thereby generating heat of high temperature, which gives rise to a problem that the heat emitted from the rotor  20  and the stator  22  is transferred to the spindle S.  
         [0011]     Meanwhile, the heat transferred to the spindle S causes fine deformation of the spindle, e.g., bending deformation, as a result of which a problem arises that the spindle cannot rotate with high precision, thereby making it impossible for a tool mounted on the spindle S to machine a work-piece with high precision. Consequently, due to the heat transferred to the spindle, poor work-pieces with inferior precision may be mass-produced.  
         [0012]     Taking this into account, a cooling device for preventing the fine deformation of a spindle has been recently proposed. As an example, Japanese Patent Laid-open Publication No. 7-185994 discloses a cooling device comprising an air supply path capable of supplying air to a motor housing and a nozzle provide at an end of the air supply path to inject the supplied air to a spindle. The cooling device renders air to be introduced into the air supply path and then injects the introduced air directly to the spindle using the nozzle to cool the spindle.  
         [0013]     Such a cooling device has an advantage of directly cooling the spindle, thus preventing the deformation of the spindle. However, because the cooling device also employs a construction that cannot cool the rotor and the stator, from which heat is generated intensively, it is impossible for the cooling device to basically prevent the generation of high temperature, as a result of which the heat generated from the rotor and the stator is continuously transferred to the spindle, whereby there is a problem in that the cooling efficiency is deteriorated.  
       SUMMARY OF THE INVENTION  
       [0014]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a cooling device for cooling a built-in-spindle type spindle motor of a machine tool, which can effectively cool a rotor and a stator, from which high temperature is generated, thereby basically blocking the heat transfer to the spindle.  
         [0015]     Another object of the present invention is to provide a cooling device for cooling a built-in-spindle type spindle motor of a machine tool, which can basically block the heat transfer to the spindle, thereby allowing the spindle to rotate with high precision and thus making it possible to produce a work-piece with high precision.  
         [0016]     In order to achieve the above-mentioned objects, there is provided a cooling device for cooling a built-in-spindle type spindle motor of a machine tool, in which the spindle motor includes a motor housing enclosing a spindle, a rotor fixed around the spindle, and a stator secured to the inner circumferential surface of the motor housing to surround the rotor with a clearance being formed between the rotor and the stator, wherein the cooling device comprises: cooling gas supply means for supplying cooling gas; a motor housing with a cooling gas introduction passage for introducing and guiding the cooling gas supplied from the cooling gas supply means to a side of the rotor and the stator; and a cooling gas injection nozzle removably installed in the motor housing and having one or more nozzle openings oriented to inject the cooling gas to the clearance between the rotor and the stator.  
         [0017]     Preferably, the cooling gas injection nozzle has a ring type body fixedly mounted on the inner circumferential surface of the motor housing to be arranged along the periphery of one side of the rotor and the stator, and wherein the ring type body comprises a flow channel formed in an annular shape along the bottom side of the ring type body to communicate with the cooling gas introduction passage, and a plurality of nozzle openings for injecting the cooling gas flowing along the flow channel toward the tip between clearance the rotor and the stator. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0019]      FIG. 1  is a side cross-sectional view showing the construction of a conventional built-in-spindle type spindle motor of a machine tool;  
         [0020]      FIG. 2  is a side cross-sectional view showing the a construction of the inventive cooling device of a built-in-spindle type spindle motor;  
         [0021]      FIG. 3 . is an exploded perspective view showing the construction of a cooling gas introduction passage and a cooling gas injection nozzle that forms the inventive spindle motor cooling device in detail; and  
         [0022]      FIG. 4  is a schematic view showing a variant of the cooling gas injection nozzle that forms the inventive spindle motor cooling device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Hereinafter, preferred embodiments for a cooling device for a built-in-spindle type spindle motor according to the present invention will be described with reference to the accompanying drawings. Components same with the conventional ones described above will be respectively indicated by the same reference numerals used in describing the prior art.  
         [0024]     Before describing the inventive spindle motor cooling device, a construction of a spindle motor is briefly described at first with reference to  FIG. 2 . As shown in the figure, the spindle motor includes a motor housing  10 . The motor housing  10  is configured to enclose a spindle S. The opposite ends of the motor housing  10  are sealed by covers  14 .  
         [0025]     In addition, the spindle motor comprises a rotor  20  fixed around the rotor  20  and a stator  22  located around the rotor  20  with a clearance being formed between the rotor and the stator. The stator  22  is secured to the inner circumferential surface of the motor housing  10 .  
         [0026]     The spindle motor further comprises a cooling device for cooling the motor housing  10 . The cooling device comprises a spiral flow passage  30  formed along the periphery of the motor housing  10 , and a fluid pump  32  for supplying fluid such as water or oil to the spiral flow passage  30 .  
         [0027]     Such a fluid-type cooling device pumps fluid with the fluid pump  32  and then supplies the pumped fluid to the spiral flow passage  30 , so that the fluid cools the motor housing  10  while passing through the spiral flow passage  30 .  
         [0028]     Next, the inventive cooling device for cooling the rotor  20  and the stator  22  is described. At first, the inventive cooling device comprises a cooling gas introduction passage  100  formed in the motor housing  10  as shown in  FIG. 2 .  
         [0029]     The cooling gas introduction passage  100  has an inlet  102  and an outlet  104 . The inlet  102  is formed toward the outside of the motor housing  10  and arranged to introduce cooling gas, e.g., cooling air, cooling gas or the like. In addition, the outlet  104  is formed toward the interior of the motor housing  10  and arranged to discharge the introduced cooling gas into the interior of the motor housing  10 .  
         [0030]     Referring again to  FIG. 2 , the inventive cooling device comprises cooling gas supply means for supplying cooling gas to the cooling gas introduction passage  100 . The cooling gas supply means consists of a pneumatic pressure source  110 , e.g., a pneumatic pump.  
         [0031]     Such a pneumatic pump  110  pumps cooling air and renders the pumped cooling air to be introduced into the cooling gas introduction passage  100 . Here, the pneumatic pressure source  110  is connected with the cooling gas introduction passage  100  of the motor housing  10  through a pneumatic line  112 , in which the pneumatic line  112  is sequentially provided with a filter  114  for filtering the cooling air and a pressure control valve  116  for controlling the pressure of the cooling air.  
         [0032]     Referring to  FIGS. 2 and 3 , the inventive cooling device comprises a cooling gas injection nozzle  120  to inject the cooling air discharged from the outlet of the cooling gas introduction passage  100  to the rotor  20  and the stator  22 .  
         [0033]     The cooling gas injection nozzle  120  has a ring type body  122 . The ring type body  122  is located around the spindle S and removably mounted on the inner circumferential surface of the motor housing  10 . Here, the inner circumferential surface of the motor housing  10  is formed with an annular seating part  16  so that the ring type body  122  can be stably seated on the seating part  16 , and a plurality of screw holes  16  are formed in the seating part  16 . Screws  18  are threaded into the screw holes  16  through the ring type body  122 . As the screws  18  are threaded into the screw holes  16  through the screw holes  16   a  in this manner, the ring type body  122  is removably installed in the motor housing  10 .  
         [0034]     The bottom side of the ring type body  122  is formed with a flow channel  124  communicated with the outlet  104  of the cooling introduction passage  100 . The flow channel  124  is formed in an annular shape along the bottom side of the ring type body  122 . Such a flow channel  124  serves to guide the cooling air discharged from the cooling gas introduction passage  100  along the inner circumferential surface of the motor housing  10 .  
         [0035]     In addition, a plurality of nozzle openings  126  are formed on the top side of the ring type body  122  to inject the cooling air in the flow channel  124  toward the rotor  20  and the stator  22 . The nozzle openings  126  are equally spaced along the ring type body  122 .  
         [0036]     These nozzle openings  126  serve to directly cool the rotor  20  and the stator  22  both generating high temperature by injecting the cooling air in the flow channel  124  toward the rotor  20  and the stator  22 . In particular, the nozzle openings  126  serve to basically block the generation of high temperature by directly cooling the rotor  20  and the stator  22  both generating high temperature. Furthermore, as the nozzle openings  126  evenly inject the cooling air while following along the periphery of the bottom side of the rotor  20  and stator  22  under the rotor  20  and stator  22 , the entire of the rotor  20  and the stator  22  are more efficiently cooled.  
         [0037]     Meanwhile, the nozzle openings  126  of the ring type body  122  are arranged to face the rotor  20  and the stator  22 , in particular the intermediate position between the rotor  20  and the stator  22 . This is to inject the cooling air to the clearance t between the rotor  22  and the stator  22  because the high temperature is mainly generated from the area where the rotor  20  and the stator  22  come into contact with each other. Accordingly, by injecting the cooling air to the clearance t between the rotor  20  and the stator  22 , it is possible to efficiently cool the high temperature generating area.  
         [0038]     The cooling air injected toward the clearance t between the rotor  20  and the stator  22  moves along the clearance t and fully cools the rotor  20  and the stator  22 . In addition, the cooling air is discharged to the opposite side to the rotor  20  and the stator  22  after cooling the rotor  20  and the stator  22 .  
         [0039]     Returning again to  FIG. 2 , the inventive cooling device comprises a vent passage for venting the cooling air, which has been discharged to the opposite side to the rotor  20  and the stator  22 , out of the motor housing I O. The vent passage  130  is formed on a cover  14  of the motor housing  10 . Such a vent passage  130  serves to quickly discharge outwardly the cooling air discharged from between the rotor  20  and the stator  22 . Meanwhile, although the vent passage  130  is shown as being formed in the cover  14  of the motor housing  10 , it is possible to form such a vent passage, e.g., directly on the motor housing  10 .  
         [0040]     Next, a working example of the present invention is described with reference to  FIG. 2 . At first, cooling air is pumped from the pneumatic pressure source  110 . Then, the pumped cooling air is introduced into the cooling gas introduction passage  100  of the motor housing  10  by way of the pneumatic pressure line  112 . At this time, the cooling air is filtered and controlled to have an appropriate pressure while passing through the filter  114  and the pressure control valve  116 .  
         [0041]     In addition, the cooling air introduced into the cooling gas introduction  100  flows to the outlet  104  and then flows into the flow channel  124 , and the cooling air flowing into the flow channel  124  moves along the flow channel  124 . Then, the cooling air moving along the flow channel  124  is injected around the bottom sides of the rotor  20  and the stator  22  through the nozzle openings  126 . In particular, the cooling air is injected to the clearance t between the rotor  20  and the stator  22 .  
         [0042]     Meanwhile, the cooling air injected to the clearance t between the rotor  20  and the stator  22  absorbs the high temperature generated from the rotor  20  and the stator  22  while rapidly moving along the clearance t between the rotor  20  and the stator  22 , thereby fully cooling the rotor  20  and the stator  22 . Then, the cooling air is discharged to the opposite side of the rotor  20  and the stator  22  after cooling the rotor  20  and the discharged cooling air is outwardly vented through the vent passage  130  of the cover  14 .  
         [0043]     According to such working of the present invention, the cooling air is directly injected to the rotor  20  and the stator  22 , thereby making it possible to directly cool the rotor  20  and the stator  22  which are the source of high temperature. In particular, by blowing the cooling air into the clearance t between the rotor  20  and the stator  22  which are the main source of high temperature, it is possible to basically block the generation of high temperature.  
         [0044]      FIG. 4  shows a variant of the inventive cooling gas injection nozzle  140 . The cooling gas injection nozzle  120  of the variant further comprises a plurality of guiders  140  for directly guiding the cooling air injected from the nozzle openings  126  to the clearance t between the rotor  20  and the stator  22 .  
         [0045]     The guiders  140  are guide tubes integrally formed with the ring type body  122  and extending toward the clearance t between the rotor  20  and the stator  22  so as to guide the cooling air injected from the nozzle openings  126  to the clearance t between the rotor  20  and the stator  22  so that more cooling air can be flown into the clearance t between the rotor  20  and the stator  22 , thereby maximizing the cooling effect.  
         [0046]     As described above, according to the inventive spindle motor cooling device, as cooling air of high pressure is directly injected to a rotor and a stator, it is possible to directly cool the rotor and the stator which are the source of generating high temperature. In particular, by blowing cooling air into a clearance between the rotor and the stator which are the main source of generating high temperature, it is possible to basically block the generation of high temperature, thereby maximizing the cooling effect.  
         [0047]     While the invention has been shown and described with reference to certain preferred embodiments thereof for the purpose of exemplification, the present invention is not limited to the specific embodiment. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
A cooling device for cooling a built-in-spindle type spindle motor of a machine tool, in which the spindle motor includes a motor housing enclosing a spindle, a rotor fixed around the spindle, and a stator secured to the inner circumferential surface of the motor housing to surround the rotor with a clearance being formed between the rotor and the stator, wherein the cooling device comprises: a cooling gas supply source for supplying cooling gas; a motor housing with a cooling gas introduction passage for introducing and guiding the cooling gas supplied from the cooling gas supply source to one side of the rotor and the stator; and a cooling gas injection nozzle removably installed in the motor housing and having one or more nozzle openings oriented to inject the cooling gas to the clearance between the rotor and the stator.