Abstract:
An electric impact tightening tool in which the rotation of an output section of an electric motor is transmitted to an impact generation section (P) and impact force generated in the impact generation section (P) causes a main shaft ( 107 ) to produce strong torque, where the electric motor is an outer rotor electric motor (M). The outer rotor electric motor (M) has low-speed, high-torque characteristics. In the tool, the impact generation section (P) and a rotor flange ( 61 ) at the forward end of the motor (M) are adapted to rotate integrally. The electric impact tightening tool is small sized and lightweight, produces low reaction force, and has durability.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electric impact tightening tool. 
       BACKGROUND ART 
       [0002]    In a conventional electric impact tightening tool, as disclosed, for example, in Japanese Patent Laid-Open No. 5-123975, the rotation of an output shaft of an inner-rotor electric motor is usually transmitted to an impact generation section via a reducer and an impact force generated in the impact generation section causes a strong torque on a main shaft. 
         [0003]    However, the above-described conventional electric impact tightening tool has problems as described below. 
       (Problem 1) 
       [0004]    In an inner-rotor electric motor, as shown in  FIG. 20 , torque is transmitted from a magnet g to a rotor r and then a thin and brittle output shaft s which is press fitted into the rotor, and further to an impact generation section through a socket k provided at a forward end of the output shaft s. 
         [0005]    The rotation speed of the impact generation section decreases at a stroke due to generation of a high torque as resistance to tightening from seating of a bolt or the like increases. Each time a high torque is generated, therefore, such decrease causes a large torsional force to act on the output shaft of the electric motor which would rotate at a constant speed. 
         [0006]    As a result, the output shaft s and the rotor r or the press-fitted part of the socket k failed to slide on each other properly and resulting in failure of the transmission of the force. In case of a brush type motor, the proper positional relation between a commutator and a rotor is lost, and this electric motor ceases to work properly in a short time or does not work any more. 
         [0007]    To solve the above-described problem, the output shaft s needs to be thicker. In this case, however, an electric motor to be used must be larger by one size or two sizes. 
       (Problem 2) 
       [0008]    In case of a brushless inner-rotor electric motor, which is small-sized to be used in a wrench, the no-load rotation speed increases to the order of 40000 to 50000 rpm when high power is input and, therefore, the rotation speed is reduced mainly by increasing the number of magnetic poles so as to increase torque. 
         [0009]    In reducing the rotation speed by the above method, taking the size and weight of the electric motor into consideration, the number of magnetic poles could be increased double or so at the most, and such increase in number reduces the rotation speed to ½ or so. Therefore, a relatively large speed reducer becomes necessary and consequently the electric impact tightening tool increases in weight by the weight of the speed reducer. 
       (Problem 3) 
       [0010]    An electric impact tightening tool using an inner-rotor electric motor usually includes a speed reducer (a planetary gear mechanism) and, therefore, the power output is increased by the speed being reduced. Being received by an inner gear, the power is transmitted to an outer case. Therefore, a worker receives the power transmitted to the case and feels it as a relatively large reaction force, which results in deteriorating workability and increasing the degree of the worker&#39;s fatigue, and then the worker cannot work using the electric tightening tool for long hours. 
         [0011]    Thus, the industries using and handling electric impact tightening tools have been awaiting development of an electric impact tightening tool that is small in size and light in weight, produces a low reaction force, and has durability. 
       SUMMARY OF THE INVENTION 
       [0012]    It is therefore an object of the present invention to provide an electric impact tightening tool that is small in size and light in weight, has a low reaction force and durability. 
         [0013]    In an electric impact tightening tool according to the present invention, the rotation of an output section of an electric motor is transmitted to an impact generation section and an impact force generated in the impact generation section causes a strong torque on a main shaft and the foregoing electric motor is an outer-rotor electric motor. This outer-rotor electric motor may have low-speed, high-torque characteristics. The impact generation section may rotate simultaneously with a rotor flange portion at a forward end of the outer-rotor electric motor together as if they were one body. 
         [0014]    The electric impact tightening tool according to the present invention can be small in size and in weight, and has a low reaction force and durability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a sectional view of main portions of an electric impact tightening tool (an electric impulse wrench) in Embodiment 1 of the present invention. 
           [0016]      FIG. 2  is a transverse sectional view of an outer-rotor electric motor incorporated in the foregoing electric impulse wrench. 
           [0017]      FIG. 3  is a longitudinal sectional view of the outer-rotor electric motor incorporated in the foregoing electric impulse wrench. 
           [0018]      FIG. 4  is a diagram to explain the principle of working of the above outer-rotor electric motor. 
           [0019]      FIG. 5  is a diagram to explain the principle of working of the above outer-rotor electric motor. 
           [0020]      FIG. 6  is a diagram to explain the principle of working of the above outer-rotor electric motor. 
           [0021]      FIG. 7  is a diagram to explain the principle of working of the above outer-rotor electric motor. 
           [0022]      FIG. 8  is a diagram to explain the principle of working of the above outer-rotor electric motor. 
           [0023]      FIG. 9  is a sectional view of a hydraulic pulse generation section. 
           [0024]      FIG. 10  is a series of sectional views of the hydraulic pulse generation section of the above electric impact wrench in use, taken along line A-A of  FIG. 9 , which includes a first to a fifth stage in one revolution. 
           [0025]      FIG. 11  is an enlarged sectional view of the first stage in the above hydraulic pulse generation section. 
           [0026]      FIG. 12  is an enlarged sectional view of the second stage in the above hydraulic pulse generation section. 
           [0027]      FIG. 13  is a perspective view of a main shaft. 
           [0028]      FIG. 14  is another perspective view of the main shaft. 
           [0029]      FIG. 15  is an explanatory diagram of a rotor of an outer-rotor electric motor in another example. 
           [0030]      FIG. 16  is an explanatory diagram of a rotor of an outer-rotor electric motor in another example. 
           [0031]      FIG. 17  is a sectional view of an electric impact tightening tool (an electric wrench having a hammer type impact mechanism section) in Embodiment 2 of the present invention. 
           [0032]      FIG. 18  is a sectional view of an electric impact tightening tool (an electric wrench having a clutch type impact mechanism section) in Embodiment 3 of the present invention. 
           [0033]      FIG. 19  is a conceptual diagram of an electric wrench in a referential example. 
           [0034]      FIG. 20  is a transverse sectional view of an inner-rotor electric motor. 
           [0035]      FIG. 21  is a longitudinal sectional view of the inner-rotor electric motor. 
           [0036]      FIG. 22  is a longitudinal sectional view of an outer-rotor electric motor. 
           [0037]      FIG. 23  is an explanatory diagram of an outer-rotor electric motor in another example. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0038]    Preferred Embodiments for carrying out an electric impact tightening tool of the present invention will be described below with reference to the drawings. 
       Embodiment 1 
       [0039]    Embodiment 1 relates to an electric impulse wrench R, one kind of the electric impact tightening tool of the present invention. 
         [0040]    This electric impulse wrench R directly transmits the rotation of a rotor  6 , which is an output section of an outer-rotor electric motor M, as shown in  FIG. 1 , to a liner  102  of a hydraulic pulse generation section P (corresponding to the impact generation section described in the section of Summary of the Invention), and, by an impact pulse generated in the hydraulic pulse generation section P, generates a strong torque on a main shaft  107 . And the outer-rotor electric motor M is driven to rotate with a battery power supply  7 . 
         [0041]    As shown in  FIGS. 1 to 3 , the outer-rotor electric motor M includes a support  1 , a rotary shaft  2 , stators  3 , coils  4 , magnets  5  and a rotor: the support  1  has a cylindrical portion  10  and a flanged portion  11  provided on a side of one end of the cylindrical portion; the rotary shaft  2  is provided via inner races of a pair of bearings B provided within the cylindrical portion  10 ; the stators  3  are fixed to an outer circumferential surface of the cylindrical portion  10  and have six magnetic pole portions  30 ; the coils  4  are wound around the stators  3 ; the magnets  5  are attached to an inner surface side of a barrel portion  60  having a gap from an outer circumferential side of the stators  3 ; and the rotor  6  has the barrel portion  60  holding the magnets  5  on its inner circumferential surface, a rotor flange portion  61  tightly fitted onto the rotary shaft  2  and a socket portion  62  provided on the rotor flange portion  61 . As shown in  FIG. 1 , this outer-rotor electric motor M is installed within the main wrench body by means of the support  1  fixed thereto with a screw and the like, not illustrated, so as not to drop. 
         [0042]    In this outer-rotor electric motor M, the rotor  6  is driven to rotate on the principle as shown in  FIGS. 4 to 8 . Coils  4  around stators  3  excite an S pole and an N pole in two poles (two teeth) (only the excited poles are indicated by solid lines), and an N pole and an S pole of the rotor  6  are attracted to the coils  4  of the stators  3 . Magnetic pole pairs of the rotor  6  are arranged every angle of 360°/7=51.43°, and poles of the stators  3  are arranged every angle of 360°/6=60°. 
         [0043]    (A) The excited positions of the coils  4  around the stators  3  shift by an angle of 60° (a change from a posture in  FIG. 4  to a posture in  FIG. 5 ). 
         [0044]    (B) When the excited positions shift or rotate by an angle of 60° as stated above, a magnet  5  of the rotor  6  are attracted in response to this rotation. More specifically, a magnet ( 3 ) out of the magnets  5  of the rotor  6 , which is closest to the magnetic pole portion  30  of the excited stator  3 , is attracted (a change from the posture of  FIG. 5  to a posture of  FIG. 6 ). In other words, while the magnetic poles of the coils  4  around the stators  3  make a 60° rotation, the rotor  6  rotates by an angle of 8.57° (360°/42) (calculating formula: 360°/6−360°/7=360°/42). 
         [0045]    (C) The excited positions of the coils  4  around the stators  3  further rotate by an angle of 60° (a change from the posture in  FIG. 6  to a posture in of  FIG. 7 ). In response thereto, a magnet ( 5 ) out of the magnets  5  of the rotor  6  is attracted, and the rotor  6  rotates by an angle of 8.57° (360°/42) (a change from the posture in  FIG. 7  to a posture in  FIG. 8 ). 
         [0046]    (D) The rotor  6  is caused to rotate by repeating the above (A) to (C). When the magnetic poles of the stators  3  revolve once (6×60°), the rotor  6  rotates by 360°/7. Under the same efficiency, a 7-fold torque is obtained. 
         [0047]    In the hydraulic pulse generation section P, as shown in  FIGS. 1 and 9 , a liner  102  is provided within a liner case  101 , and a main shaft  107  is fitted into the liner  102  so that the liner  102  is rotatable with respect to the main shaft  107 . Working fluid (oil) for generating torque is filled in this liner  102 , and the liner  102  is sealed with a liner bottom plate  103  and a liner top plate  104  attached to both ends of the liner  102 . 
         [0048]    As shown in  FIG. 9 , the liner bottom plate  103  has a hole  130  through which the main shaft  107  is inserted, and a chamber  108  formed between a constituting wall surface of the hole  130  and an outer circumferential surface of the main shaft  107  receives an O-ring  180  for ensuring air tightness (fluid tightness) therebetween. 
         [0049]    The liner case  101  and the liner  102  are coupled together, and driven to rotate together as if they were one in response to the rotation of the outer-rotor electric motor M. 
         [0050]    The interior of the liner  102  is shown in  FIG. 11 , and a liner chamber  120  having a cross section in the form of an ellipse is formed therein. Blades  105  are inserted in two opposing grooves  170  and  170  of the main shaft  107  via a spring  106 , and contractibly abut against an inner surface of the liner  102  having a cross section in an elliptical form. As shown in  FIGS. 13 and 14 , the outer surface of the main shaft  107  is provided with second sealing faces  171  and  172  which are two protruding ribs positioned oppositely on the outer surface between the two blades  105  and  105 . One of the second sealing faces  171  is formed in a stepped shape as shown in  FIG. 13 , while the other second sealing face  172  is linearly formed as shown in  FIG. 14 . 
         [0051]    The inner circumferential surface of the liner  102 , as shown in  FIG. 11 , is provided with first sealing faces  121 ,  122 ,  123  and  124  which are respectively projecting in a mound shape at both ends of the major axis of the elliptical section and on both sides of the minor axis thereof. And only once while the liner  102  is making one revolution with respect to the main shaft  107 , as shown in ( 1 ) and ( 2 ) of  FIG. 10 ,  FIG. 11  and  FIG. 12 , the first sealing face  121  and the second sealing face  171 , the first sealing face  122  and the second sealing face  172 , the first sealing face  123  and an outer end surface of one of the blades  105 , and the first sealing face  124  and an outer end surface of the other blade  105  respectively coincide with each other (they coincide so as to maintain an air-tightness in the whole area in the axial direction of the main shaft  107 ). As a result, the liner chamber  120  is hermetically divided into four chambers: two high-pressure chambers H and two low-pressure chambers L. To realize this, the first sealing face  121  is formed in the stepped shape in the same manner as the second sealing face  171 , and the first sealing face  122  is formed linearly in the same manner as the second sealing face  172 . 
         [0052]    The above-mentioned hydraulic pulse generation section P is constituted as stated above, and a two-blade type impulse wrench R employing this hydraulic pulse generator P functions as follows. 
         [0053]    Operation of a lever SL actuates the outer-roller electric motor M to rotate at a high speed and, in response thereto, the liner  102  also rotates. 
         [0054]    In response to the rotation of the liner  102 , the liner chamber  120  changes every 90° intervals as shown in ( 1 )( 2 )-( 3 )-( 4 )-( 5 ) of  FIG. 10  while the liner  102  makes one revolution. 
       Postures in ( 1 ) and ( 2 ) of FIG. 10 
       [0055]    In the postures in ( 1 ) of  FIG. 10  and in  FIG. 11  showing an enlarged view thereof, the first sealing face  121  and the second sealing face  171 , the first sealing face  122  and the second sealing face  172 , the first sealing face  123  and an outer end surface of one of the blades  105 , and the first sealing face  124  and an outer end surface of the other blade  105  respectively coincide with each other (they respectively coincide so as to maintain an air-tightness in the whole area in the axial direction of the main shaft  107 ). As a result, the liner chamber  120  is hermetically divided into four chambers: two high-pressure chambers H and two low-pressure chambers L. 
         [0056]    And as shown in ( 2 ) of  FIG. 10  and in  FIG. 12  showing an enlarged view thereof, when the liner  102  rotates further responsive to the rotation of the outer-rotor electric motor M, the volume of each of the high-pressure chambers H decreases, the oil therein is compressed, and instantaneously a high pressure is generated. This high pressure forces the blades  105  toward the low-pressure chambers L. Couple of force acts instantaneously on the main shaft  107  via the upper and lower blades  105  and  105 , which generates a strong torque. 
       Posture in ( 3 ) of FIG. 10 
       [0057]    ( 3 ) of  FIG. 10  shows a posture in which the liner has made a 90° rotation after the generation of torque on the main shaft  107 . 
         [0058]    In the liner chamber  120 , each of the high-pressure chambers H and each of the low-pressure chambers L communicate with each other and form respective unified chambers having the upper and lower blades  105  and  105  therebetween. Here no torque is generated and the liner  102  further rotates in response to the rotation of the outer-rotor electric motor M. 
       Posture in ( 4 ) of FIG. 10 
       [0059]    ( 4 ) of  FIG. 10  shows another posture in which the liner has made a further 90° rotation from the posture in ( 3 ) of  FIG. 10 , namely a 180° rotation from an impacting blow. 
         [0060]    The first sealing face  121  and the second sealing face  172  do not coincide with each other, while the first sealing face  122  and the second sealing face  171  do coincide with each other only with a tiny portion. Therefore between the sealing faces exists no sealing, pressure doesn&#39;t change and torque is not generated. The liner  2  continues to rotate. 
       Posture in ( 5 ) of FIG. 10 
       [0061]    ( 5 ) of  FIG. 10  shows another posture in which the liner has made a further 90° rotation from the posture in ( 4 ) of  FIG. 10 , namely a 270° rotation from the impacting blow. 
         [0062]    This posture is substantially the same as that in ( 3 ) of  FIG. 10  and no torque is generated. With a further rotation, the liner returns to the posture in ( 1 ) of  FIG. 10 , and then the first sealing face  121  and the second sealing face  171 , the first sealing face  122  and the second sealing face  172 , the first sealing face  123  and the outer end surface of one of the blades  105 , and the first sealing face  124  and the outer end surface of the other blade  105  respectively coincide with each other, which generate another impacting blow force. 
         [0063]    As stated above, one impacting blow force is generated per revolution of the liner  102 . 
         [0064]    The manner of coupling between the outer-rotor electric motor M and the hydraulic pulse generation section P is shown in  FIG. 1 . A hexagonal part of the liner top plate  104  of the hydraulic pulse generation section P is inserted into the socket portion  62  of the outer-rotor electric motor M so that rotation is transmitted. 
         [0065]    This electric impulse wrench R has the following advantageous features. 
         [0066]    (1) In an inner-rotor electric motor, as shown in  FIG. 21 , the diameter of a rotor  6 ′ is about ⅔ of the outside diameter of a motor, whereas in an outer-rotor electric motor, as shown in  FIG. 22 , the diameter of a rotor  6  per se is the outside diameter of a motor. Therefore, when driven with the same magnetic force, the output torque of the outer-rotor electric motor becomes about 1.5 times as large as that of the inner-rotor motor. In other words, when the output torque is made the same in both the motors, the outside diameter of the outer-rotor electric motor becomes about ⅔ times smaller than that of the inner-rotor motor. 
         [0067]    Therefore, with use of an outer-rotor electric motor as a driving source, an electric impulse wrench can be downsized and reduced in weight. 
         [0068]    In one type of outer-rotor electric motor, as shown in  FIG. 22 , which has six poles of the magnetic pole portions  30  of the stators  3  and four poles of the magnets  5  on the rotor  6 , the rotation speed of the rotor  6  is the same (40000 to 50000 rpm) as the speed of the rotating magnetic field in the stators  3 . On the other hand, in the outer-rotor electric motor M of this embodiment which has six poles of the magnetic pole portions  30  of the stators  3  and  14  poles of the magnets  5  on the rotor  6 , the rotation speed of the rotor  6  becomes 1/7 (6000 to 7000 rpm) of the speed of the rotating magnetic field in the stators  3 . That is, the outer-rotor electric motor of this embodiment has not only high-torque characteristics but also low-speed characteristics. 
         [0069]    Therefore, this electric impulse wrench R does not have to have a speed reducer, and thereby can be reduced in size and weight by those of such an reducer and a worker receives less reaction force therefrom. 
         [0070]    From the viewpoint of the above two factors, compared with a conventional one, this electric impulse wrench R can be considerably downsized and reduced in weight. 
         [0071]    (2) In this electric impulse wrench R, the rotation speed of the liner  102  of the hydraulic pulse generation section P decreases at a stroke likewise due to the generation of a high torque following an increase in resistance to tightening by seating of a bolt and the like. 
         [0072]    However, in this electric impulse wrench R, a torsional force from the liner  102  is transmitted not by a conventional thin output shaft that is brittle in terms of strength, but through a route indicated by the black arrows in  FIG. 2  (the route from the socket portion  62 →the rotor&#39;s flange portion  61 →the barrel portion  60  in the rotor  6 ). Therefore, this electric impulse wrench R has very high resistance to the foregoing torsional force. 
         [0073]    Consequently, different from the conventional electric impact tightening tool as observed above in the section of Prior Art, the situation that an electric motor ceases to work properly in a short time or does not work won&#39;t happen in this electric impact tightening tool. In other words, this electric impulse wrench R has an excellent durability. 
         [0074]    (3) From the above, the constitution of this electric impulse wrench R allows the wrench R to be reduced in size and weight, and have a low reaction force and an excellent durability. 
         [0075]    Other manners of coupling the outer-rotor electric motor M and the hydraulic pulse generation section P are shown in  FIGS. 15 and 16 , in which a motor has another type of rotors  6  in place of the outer-rotor electric motor M of the above embodiment. With the constitution of this electric impulse wrench R, in addition to being small in size and weight and with a low reaction force and an excellent durability, the electric impulse wrench R further provides the following advantageous features. 
         [0076]    The constitution shown in  FIG. 15  being adopted, a joint area is present on the outer circumference of the hydraulic pulse generation section P, and consequently the wrench is allowed to have a shorter whole length and the strength that is large enough to transmit force. 
         [0077]    In the constitution in  FIG. 16 , the hydraulic pulse generation section P and the rotor  6  of the outer-rotor electric motor M are formed in one body. In this case, a joint area being unnecessary, the whole length of the wrench could be reduced. 
         [0078]    The features and constitutions stated above hold true in Embodiments 2 and 3 described below. 
       Embodiment 2 
       [0079]    Embodiment 2 relates to an electric hammer wrench R 1 , one kind of the electric impact tightening tool of the present invention, having a hammer type impact mechanism  8  (corresponding to the impact generation section described in the section of Summary of the Invention). 
         [0080]    As shown in  FIG. 17 , this electric hammer wrench R 1  has a hammer impact mechanism  8  including a hammer  80  and an anvil  81 . When the hammer  80  rotates in response to the rotation of an outer-rotor electric motor M and gives an impacting blow to the anvil  81 , an impact force is generated in the anvil  81 . The impact force is transmitted to a bolt and the like as torque, and they are tightened. An impact force is generated once per revolution of the hammer  8 . 
         [0081]    This electric hammer wrench R 1  also employs an outer-rotor electric motor M like in Embodiment 1 and, therefore, apparently advantageously functions likewise. 
       Embodiment 3 
       [0082]    Embodiment 3 relates to an electric clutch wrench R 2 , one kind of the electric impact tightening tool of the present invention, having a clutch type impact generation section  9  (corresponding to the impact generation section described in the section of Summary of the Invention). 
         [0083]    As shown in  FIG. 18 , this electric clutch wrench R 2  has a clutch type impact generation section  9  provided with a clutch section  90  having a lower clutch  90   a  and an upper clutch  90   b  engaging therewith, a main shaft  91 , and a coil spring  92  that forces to push the upper clutch  90   b  toward the lower clutch  90   a . The rotational force of an outer-rotor electric motor M is transmitted to the main shaft  91  via the clutch section  90  as tightening torque. 
         [0084]    In the clutch type impact generation section  9  in this electric clutch wrench R 2 , engaging part  93  between the lower clutch  90   a  and the upper clutch  90   b  is in the manner that respective tapered clutches engage each other. When a bolt and the like are tightened with not less than a specific torque, the force of the lower clutch  90   a  that is going to stop becomes larger than the engaging force of the engaging part  93  and consequently the upper clutch  90   b  disengages from the lower clutch  90   a  (the upper clutch  90   b  climbs over tapered part of the lower clutch  90   a ). After that, the upper clutch  90   b  again engages with the lower clutch  90   a . These engagement and disengagement are repeated and an impact force is generated each time when the upper clutch  90   b  disengages from the lower clutch  90   a  (see  FIG. 18 ). 
         [0085]    This electric hammer wrench R 2  also employs an outer-rotor electric motor M like in Embodiment 1 and, therefore, apparently advantageously functions likewise. 
         [0086]    The electric impact tightening tools in Embodiments 1 to 3 stated above are some examples. As long as electric impact tightening tools are constituted in the manner that the rotation of an output section of an outer-rotor electric motor is transmitted to an impact generation section and an impact force generated in this impact generation section causes a strong torque on the main shaft, such tools fall in the technical scope of the present invention. 
         [0087]    In the above-described embodiments, six magnetic pole portions  30  are provided in the stator part  3 . Another possible example is to provide 12 portions to be able to be magnetic pole portions  30  on the stator part  3  and wind a coil  4  around every other portions. 
         [0088]    Furthermore, the number of magnetic pole portions  30  formed on the stator part  3  is not limitative to six, but changeable as required. 
         [0089]    The outer-rotor electric motor M can be used in an electric wrench of the type shown in  FIG. 19 . In this electric wrench, the rotation of the outer-rotor electric motor M is transmitted through a two-stage or three-stage planetary gear  75 →a pair of bevel gears  76 →an output shaft  77  and tightens a screw and the like. In this electric wrench, the outer-rotor electric motor M allows to reduce the number of stages of the planetary gear as stated above and consequently to reduce the weight of the whole wrench.