Abstract:
A compact terminal unit for an electric motor capable of switching over windings with ease and improving automation of assembling and inspection process of the electric motor. A terminal base is fixed at a position of a through hole formed on a housing of the electric motor. Leads of the windings of a rotor are connected with cylindrical presser portions of lead connectors by caulking. A conducting portions of the lead connectors are inserted into mounting portions of the terminal base. The power cables are connected with conducting portions with screws engaged with the conducting portions so that the power cables are electrically connected with leads of the windings. Since the leads are connected to the lead connectors with their orientations vertically under the power cable connection terminals not to be present in a space in a terminal box, an ample space for attachment of the power cables to the power cable connection terminals is secured. The switchover of windings from a delta connection to star connection and vice versa can be easily performed. Since positions and orientation of the leads are fixed at mounting portions of the terminal base, the inspection of the windings can be easily performed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electric motor, and in particular to a terminal unit for connecting leads of stator windings of the electric motor with power cables for supplying electricity from outside. 
     2. Description of the Related Art 
     FIG. 12 is a sectional view of an electric motor taken along a central axis X—X of a rotor shaft  4  of an electric motor for showing an arrangement of a conventional terminal unit mounted on a housing of an electric motor. The electric motor shown in FIG. 12 is a three-phase electric motor for driving a spindle of a machine tool. 
     In FIG. 12, a housing  1  of the electric motor has a through hole  9  through which leads  7  from windings of respective phases U, V and W of a stator  2  are drawn out of the housing  1 . A terminal box  10  having a terminal base  80  formed integrally therewith is mounted on the housing  1 . The leads  7  of respective phases drawn through the through hole  9  are led into the terminal box  10 , and ends of the leads  7  are respectively connected with conductive plates  81  by means of terminal members  83 . In FIG. 12, reference numerals  3 , and  5  denote a rotor and a fan for cooling the electric motor, respectively. 
     FIG. 13 is a top plan view of the terminal unit shown in FIG.  12 . The terminal members  83  fixed to ends of the respective leads  7  are connected to the conductive plates  81  on the terminal base  80  by means of screws  82 . Terminal member  84  connected with respective ends of the power cables  70  are connected to the conductive plates  81  by means of screws  82 . FIG. 13 shows an example of connection of the three leads  7  and the three power cables  70 . 
     As described, in the conventional terminal unit, the terminal base  80  is formed integrally with the terminal box  10  or assembled in the terminal box  10  to have an integral structure. In manufacturing the electric motor, the stator  2 , the rotor  3 , the cooling fan  5 , etc. are manufactured respectively through separate processes and are assembled together in a final assembling process. In the final assembling process, the leads  7  are drawn out of the housing  1  through the through hole  9  and let into the terminal box  10 , and then the terminal box  10  is mounted on the housing  1 . After the terminal box  10  is mounted on the housing  1 , the terminal members  83  of the leads  7  are connected to the conductive plates  81  by rotating the screw  82  manually. 
     In order to improve an output power specification of the electric motor, a method of obtaining optimum velocity and torque characteristics particularly required for the electric motor has been adopted by switching over connection of windings from a star connection to a delta connection and vice versa. In this case, the three terminal connection have to be changed to six terminal connection for the switch over of the windings. In order to change to the six terminal connection, a size of the terminal base has to be made at least twice as large as the three terminals and also the terminal box has to be made larger, to hinder saving space and saving resources. Since the industry of manufacturing of machine tools, etc. has trended to saving space and saving resources, the conventional arrangement of the terminal unit is counter to the trend. 
     Particularly, if power cables of large diameters are used for adaptation to a safety standard, radiuses of curvature of the power cables are enlarged to make it difficult to connect them with the power cable connection terminals provided in the terminal box. 
     As described, connection of the leads with the power cable connection terminals is performed manually. It is not preferable that the manual operations and automatic operations are admixed in an assembling line in view of efficiency and safety, and it has been desired to render all the operations automatic. 
     The leads are tend to have random orientations since the leads are tend to be bent with their flexibility and it is difficult to fix the position and orientations of the leads. Thus, it is difficult to automatically screw the terminals on the terminal base. Further, in an automatic inspection of the windings of the stator, it is difficult to bring a prove in contact with the leads to make the automatic inspection hardly possible. With the above factors, a full automation of the assembling process of the electric motor has been impeded. 
     SUMMARY OF THE INVENTION 
     The present invention provides a terminal unit for an electric motor capable of obtaining an output specification of the electric motor by switching the connection of the windings with the same size as the conventional terminal unit, and also improving automation of assembling and inspection process of the electric motor. 
     According to a first aspect of the present invention, a terminal unit for an electric motor comprises: a terminal base fixed at a periphery or in a vicinity of a through hole formed on a housing of the electric motor; a power cable connection terminal arranged at an outer portion of the terminal base, for connection with the power cable; and a lead connector connected with the lead and arranged inner than the power cable connection terminal in a radial direction of the electric motor, and the power cable connection terminal and the lead connector are electrically connected with each other. With the above arrangement, the leads are arranged out of a terminal box and thus the leads are prevented from occupying any substantial space in a terminal box to allow the power cable to occupy a sufficient space in the terminal box. 
     The leads may be connected with the lead connectors at an inner position of the terminal base in the radial direction of the electric motor and the power cables are to be connected with the power cable connection terminals at an outer position of the terminal base in the radial direction of the electric motor. The leads may be connected with the lead connectors with substantially the same orientation as the lead are drawn out of the housing, and the power cables may be connected with the power cable connection terminals in a plane substantially parallel to an outer surface of the housing. 
     The terminal base may be positioned above the through hole formed on the housing and at an extremity in a terminal box. 
     According to a second aspect of the present invention, a terminal unit for an electric motor comprises: a terminal base fixed at periphery or in vicinity of a through hole formed on a housing of the electric motor; power cable connection terminals arranged on the terminal base, for connection with the power cables; and lead connectors arranged on the terminal base, each of the lead connectors having a presser portion connected with the lead and a conducting portion formed integrally with the presser portion and connected with the power cable connection terminal. 
     The power cable connection terminal may comprise a screw terminal, the lead connector has a form of a hook, the leads are connected with the presser portion in the radial direction of the electric motor, and an end part of the conducting portion is fitted to a rod of the screw terminal in an axial direction of the electric motor. The conducting portion may have a female screw and the conducting portion is connected with the power cable connection terminal by an threaded engagement of the screw terminal with the female screw. The presser portion is formed cylindrically with an end closed by a wall and a window is formed at a side of the cylindrical presser portion for confirming an end of the lead. 
     The lead connector has a linear form, the power cable connection terminal comprises a screw terminal, the leads are connected with the presser portion in the radial direction of the electric motor, and an end part of the conducting portion is fitted to a rod of the screw terminal in the radial direction of the electric motor. 
     The presser portion may have a cylindrical shape into which the lead is inserted and fixed by caulking, the conducting portion has a wall between the presser portion and an end part connected with the power cable connection terminal, for preventing access of an end of the lead inserted into the presser portion to the end part of the conducting portion by abutting with the end of the lead. The wall may be formed by bending the conducting portion or formed by adding an additional member to the conducting portion. A window may be formed by a gap between an end face of the presser portion and the wall for confirming and end of the lead. 
     Further, according to a third aspect of the present invention, a terminal unit for an electric motor comprises: a terminal base fixed at periphery or in vicinity of a through hole formed on a housing of an electric motor and having lead connector mounting portions; and lead connectors fixed at the lead connector mounting portions of the terminal base, each of the lead connectors having a power cable connection terminal for connection with the power cables, a presser portion for connection with the leads by pressing and a conducting portion for electrically connecting the power cable connection terminal and the presser portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an electric motor along a rotor axis, having a terminal unit according to an embodiment of the present invention; 
     FIG. 2 is a top plan view of the terminal unit as shown in FIG. 1; 
     FIG. 3 is a top plan view of a terminal unit with three power cable connection terminals; 
     FIGS. 4 a - 4   d  are an elevation view, a top plan view, a bottom plan view, a right side view, respectively, of the lead connector as shown in FIGS. 1-3; 
     FIGS. 5 a - 5   e  illustrate attachment of the lead connector to a terminal base, of which FIG. 5 a  and FIG. 5 b  are a top plan view and a side view, respectively, of the mounting portion of the terminal base and the lead connector, FIG. 5 c  is an elevation view of the mounting portion of the terminal base, FIGS. 5 d  and  5   e  are a top plan view and a side view of the lead connector attached to the mounting portion; 
     FIG. 6 is a side view of an alternative example of the lead connector in which an end of the presser portion is closed; 
     FIGS. 7 a - 7   d  show an alternative of the lead connector, in which FIGS. 7 a  and  7   b  are side and perspective views of the lead connector, respectively, and FIGS. 7 c  and  7   d  are side and sectional views, respectively, of the lead connector with an end of the lead fixed; 
     FIGS. 8 a  and  8   b  are a side view and a front elevation of another alternative of the lead connector; 
     FIGS. 9 a  and  9   b  are a side view and a front elevation of still another alternative of the lead connector; 
     FIG. 10 is a schematic view of a terminal unit according to a second embodiment of the present invention; 
     FIGS. 11 a - 11   c  illustrate a terminal unit according to a third embodiment of the present invention, of which FIG. 11 a  is a front elevation view of the mounting portion of the terminal base, FIG. 11 b  and FIG. 11 c  are a top plan view and a side view, respectively, of the mounting portion of the terminal base and the lead connector, FIGS. 11 d  and  11   e  are side views of alternatives of the lead connectors for the lead connector shown in FIGS. 11 a - 11   c ; 
     FIG. 12 is a sectional view of an electric motor along a rotor axis having a conventional terminal unit; 
     FIG. 13 is a top plan view of the conventional terminal unit as shown in FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A terminal unit for an electric motor according to an embodiment of the present invention will be described referring to FIGS. 1 and 2. As shown in FIG. 1, a through hole  6  for taking out leads  7  of windings of respective phases of a stator  2  and for mounting a terminal base  20  for connecting the leads  7  with power cables  70  is formed on a housing  1  of an electric motor. The terminal base  20  is fixed on the housing  1  of the electric motor at a periphery or at least in the vicinity of the through hole  6  by means of fixtures such as set screws (not shown). In this embodiment, the terminal unit has six power cable connection terminals. As shown in FIG. 2, six terminal mounts are formed on the terminal base  20  and six lead connectors  21  are respectively attached to the six terminal mounts. The six power cable connection terminals are constituted by the six terminal mounts of the terminal base  20 , the six lead connectors  21  and six screws  24  fixed to the six lead connectors  21 . Each of the lead connectors  21  has a presser portion  22  for connection with an end of the lead  7  and a conducting portion  23  formed integrally with the presser portion  23 , for electric connection with the power cable  70 . 
     Each end of the lead  7  is connected with the lead connector  21  by the presser portion  22  formed at an end of the lead connector  21  towards the end of the lead  7 . The conducting portion  23  at the other end of the lead connector  21  is made in contact with a terminal member  84  of the power cable  70  by means of the screw  24  so that the lead  7  is electrically connected with the power cable  70 . The lead connector  21  is arranged so that the presser portion  22  is positioned below, i.e., more inside than, the conducting portion  23  and the end of the lead  7  is inserted into the presser portion  22  from underside and fitted with the presser portion  22 . Specifically, the presser portion  22  is positioned more closer to the central axis X—X of the rotor shaft  4  than the conducting portion  23  on a plane perpendicular to the central axis X—X. An upper end of the conducting portion  23  is bent at substantially right angle to come in contact with the power cable  70  at the upper position of the terminal base  20 . The terminal box  10  is arranged so as to cover the terminal base  20  and the terminal base  20  is arranged to be positioned at extremity in the terminal box  10 . A reference numeral  11  denotes a lid of the terminal box  10 . 
     The six power cable connection terminals for connection with the power cables  70  are formed stepwise, on the terminal base  20  in two rows. Three terminal mounts are provided on each row and the lead connectors  21  are mounted on the terminal mounts to form the six terminals with the screw  24 . The terminal members  84  attached to the ends of the power cables  70  are fixed to the conducting portion  23  of the lead connector  21  by means of the screw  24  to come in contact with the conducting portion  23 . 
     As shown in FIGS. 1 and 2, the terminal base  20  is positioned at the extremity in the terminal box  10  to form a sufficient space for drawing the power cables  70  with a large radius of curvature, so that power cables of large diameter can be connected to the lead connector  21  with ease. 
     FIG. 3 shows another embodiment of the terminal base having three power cable connection terminals. 
     FIGS. 4 a - 4   d  are detailed views of the lead terminal  21  shown in FIGS. 1-3. The lead terminal  21  is formed from conductive material to have a shape of a hook. The presser section  22  is formed cylindrically at the bottom of the lead terminal  21  for fitting the end of the lead  7  by caulking. The conducting section  23  is formed integrally with the presser portion  22  and bent at substantially right angle to form an end part. The end part of the presser portion  23  is formed into two forks to allow the screw  24  to be inserted therebetween. A surface of the two forks are arranged to lie perpendicular to a direction of insertion of the lead  7 . The forked end of the conducting portion  23  constitutes the power cable connection terminal cooperatively with the screw  24 . 
     FIGS. 5 a - 5   d  are detailed views showing mounting of the lead connector  21  on the terminal base  20 . 
     A nut  25  is fixed at each of the terminal mounts of the terminal base  20  by hot-melt fitting, as shown in FIGS. 5 b ,  5   c  and  5   e . The screw  24  is threadedly engaged with the nut  25 . Grooves  26  for guiding the forked ends of the conducting portion  23  are formed at the terminal mount on both sides of the screw  24 . 
     The end of the lead  7  is inserted into the cylindrical presser portion  22  of the lead connector  21  and caulked to be fixed therewith. The engagement of the screw  24  on the nut  25  is loosen to form a gap between a head of the screw  24  and the nut  25 . Then, the forked ends of the conducting portion  23  are inserted into the gap to position a threaded rod of the screw  24  therebetween. The forked ends are guided by the grooves  26  to be inserted below the head of the screw  24 , as shown in FIGS. 5 d  and  5   e . The terminal member  84  of the power cable  70  is inserted between the head of the screw  24  and the forked ends of the conducting portion  23  and the terminal member and the lead connector  21  are fastened together to be electrically connected with each other by rotating the screw  24  to be fitted with the nut  25 . Thus, the power cable  70  is connected with the lead of the winding of the rotor. 
     The attachment of the terminal base and the terminal box to the housing of the electric motor will be described. First, the ends of the leads  7  of the windings are drawn out of the housing  1  through the through hole  6  and the lead connectors  21  are fixed to the respective ends of the leads  7  by inserting the ends into the cylindrical presser portions  22  and pressing the presser portions  22  towards the respective ends. Then, the terminal base  20  is mounted on the housing at the periphery of the through hole  6 . The lead connector  21  is fitted to the terminal mount by inserting the forked ends of the conducting portion  23  into the gap between the nut  25  and the screw  24  and rotating the screw  24  to be fitted into the nut  24 . Then, the terminal box  10  is mounted on the housing  1  so that the terminal base  20  is positioned at extremity in the terminal box  10 . Finally, the lid  11  is fitted on the terminal box  10 . 
     After the assemble of the terminal base and the terminal box is completed, an inspection of the winding is performed. Since the lead connectors  21  are fitted on respective terminal mounts of the terminal base  20  to fix the positions of respective leads  7 , the inspection of the windings can be performed easily by moving a prove to the fixed positions of the leads  7 . 
     The leads  7  are connected with the lead terminals below the terminal base  20  with the substantially same orientation as the lead  7  is drawn out of the housing  1  at the position of the through hole  6 . Therefore, the leads  7  do not occupy any substantial space in the terminal box  10 . The power cables  70  are connected with the power terminals in a plane substantially parallel to an upper surface of the housing  1  in a sufficient space in the terminal box  10 . The power cables  70  can be connected with the power cable connection terminals without being bent at small radiuses of curvature, to make a connection operation easy. 
     In the above first embodiment, the forked end of the conducting portion  23  of the lead connector  21  is formed above the presser portion  22  in the direction of inserting the lead  7  into the presser portion  23 , as shown in FIG.  4 . Namely, the forked end of the conducting portion  23  is formed across a line of insertion of the lead  5  into the cylindrical presser portion  22 . With this arrangement, the end of the lead  7  may reach the forked end of the conducting portion  23  to cause an obstacle in inserting the lead connector  21  into the terminal base. Particularly, the obstacle may frequently occur in the case where the cut end of the lead  7  is not sufficiently trimmed. In the case of the lead comprising a hard and thick enamel wire, even if the cut wire is sufficiently trimmed before insertion into the presser portion  22 , the end of the lead  7  may deform to have an irregular form while inserting the end into the presser portion  22  and caulking the presser portion  22  towards the end, to disturb the fitting of the lead connector  21  to the terminal base. 
     In order to overcome the above problem, a lead connector  21 ′ having a presser portion  22 ′ with a closed end as shown in FIG. 6 may be adopted. With this structure, the inserted end of the lead  7  is brought into contact with the closed end of the presser portion  22 ′ to prevent the end of the lead  7  from obstructing the fitting of the lead connector  22 ′ into the terminal base. With this structure, however, it would be difficult to find out a lead insufficiently inserted into the presser portion  22 ′. 
     FIGS. 7 a - 7   d  show an alternative of the lead connector  21 , which is capable of preventing the end of the lead  7  from obstructing the mounting of the lead connector on the terminal base  20  and also confirming a sufficient insertion of the end of the lead  7  into the presser portion. 
     A lead connector  121  is formed from conducting material and comprises a cylindrical presser portion  122  for connection with an end of the lead  7  by caulking and a conducting portion  123  formed integrally with the presser portion  122  in the same manner as the lead connector  121  shown in FIG. 4, but different from the lead connector  121  in a structure of the conducting portion  123 . The conducting portion  123  comprises a forked end  123   a  for the power cable connection terminal, and a midsection  123   b  for connecting the forked end  123   a  and the presser portion  122 . The midsection  123   b  extends from the presser portion  122  in a direction of insertion of the lead  7  and bent at a position apart from an end of an upper end plane of the presser portion  122  at right angle to form a wall  123   c  parallel to the end plane of the presser portion  122 , and bent at right angle to extend in the direction of insertion of the lead  7  and then bent at right angle to form the forked end  123   a.    
     As shown in FIGS. 7 c  and  7   d , the end of the lead  7  is inserted into and through the presser portion  122  to be brought into contact with the wall  123   c  of the midsection  123   b  which is parallel to the upper plane of the presser portion  122 . In this insertion, a load of insertion force increases when the end of the lead  7  comes in contact with the wall  123   c  to notify an operator of the contact with the wall  123   c . A clearance between the wall  123   c  and the presser portion  122  is utilized as a window  123   d  for confirming a connection between the lead  7  and the presser portion  122 . The end of the lead  7  is arrested by the wall  123   c  not to reach the position of the forked end  123   a , not to obstruct the fitting of the lead connector  121  to allow the operator to easily fit the lead connector to the terminal base. 
     FIG. 8 shows another embodiment of the lead connecting member. The lead connecting member  221  differs from the lead connecting member  121  shown in FIG. 7 in a structure of the midsection  223   b  of the conducting plate  223 . The midsection  223   b  extending from a presser portion  222  is bent at right angle to extend parallel to an upper face of the calking portion  222  and further bent at  180 ′ to form a wall  223   c  by the folded plates for preventing access of the end of the lead  7  to the conducting plate  223 . The conducting plate  223  is then bent at right angle to extend in the direction of insertion of the lead  7  and further bent at right angle to form the forked end  223   a . A gap  223   d  is formed between the wall  223   c  and the upper end face of the presser portion  222 . The function and effects are the same as that of the lead connector  121  as shown in FIG.  7 . 
     FIG. 9 shows still another embodiment of the lead connecting member. An upper end face of a cylindrical conducting portion  322  is closed by a wall  323   c  to prevent access of the end of the lead  7 . The wall may be formed by bending the midsection  323   b  of the conducting portion  323 . A window  323   d  is formed at the upper and side position on the presser portion  322  so that state of the end of the lead  7  inserted into the presser portion  222  is confirmed through the window  323   d . In this embodiment, the end of the lead  7  is arrested by the wall  323   c  not to reach the position of the forked end  323   a , not to obstruct the fitting of the lead connector  121  to allow the operator to easily fit the lead connector to the terminal base. 
     In the above embodiments of the lead connector, the wall for preventing access of the lead  7  is formed by a part of the conducting portion. The wall may be provided by adding an additional member to the conducting portion. For example, an additional member may be added to the conducting portion  23  between the presser portion  222  and the upper end of the conducting portion  23  in FIG.  4 . 
     FIG. 10 shows a terminal base according to a second embodiment of the present invention. 
     In this embodiment, the terminal base  30  has fitting holes for fitting in lead connectors  31  at respective terminal mounting portions. The lead connector  31  comprises a presser portion  32  for connection with an end of the lead  7  by caulking, and a conducting portion  33  formed integrally with the presser portion  32 , for connection of the power cable  70 . The presser portion  32  has a cylindrical shape to form a hole inside into which the end of the lead  7  is inserted from a lower position. The conducting portion  33  has a female thread formed inside in an axial direction of the lead connector  31  (the same direction as that of the hole of the presser portion  32 ) at the central position thereof. The conducting portion  33  is fitted into the fitting hole  35  formed in the mounting portion. Then, a threaded portion of the screw  34  is brought into engagement with the female thread of the conducting member  33  of the lead connector  31 . The lead connector  31  with its conducting portion filled into the fitting hole  35  is shown on the left side of the lead terminal base at a mounting portion in the upper row. 
     In this second embodiment, each terminal comprises the lead and power terminal mounting portions of the terminal base  30 , the lead connector  31  and the screw  34 . The power terminal member of each power cable  70  is inserted between the head of the screw  34  and the conducting portion  33  of the lead connector  31  and the power terminal member is connected with the conducting portion  33 , so that the power cables  70  are electrically connected with the leads  70  from the windings of the stator. 
     FIGS. 11 a - 11   e  show a terminal unit according to a third embodiment of the present invention. 
     In this embodiment, a lead connector  41  is fitted into a fitting groove  45  formed at a terminal mount of a terminal base  40 . The arrangement of this embodiment is different from the first embodiment in that a female thread is formed at the bent end portion of a conducting portion  43  of a lead connector  41  having a larger thickness, and a screw  44  is engaged with the female thread of the conducting portion  43 . The end of the conducting portion  43  is fitted into the fitting groove  45  to fix the lead connector  41  to the mounting portion of the terminal base  40 . 
     FIG. 11 d  shows an alternative of the lead connector in this embodiment. A nut  55  is fixed by welding on an end of a conducting portion  53  of a lead connector  51 . The end of the lead connector  51  with the nut  55  is inserted into the groove formed at the mounting portion of the terminal base. 
     FIG. 11 e  shows another alternative of the lead connector. A protrusion  65  is formed at an end of a conducting portion  63  by a burring process and a female thread is formed at the protrusion  65  to be engaged with a nut  64 . The end of the lead connector  61  with the protrusion  65  is inserted into the groove formed at the mounting portion of the terminal base. 
     In the above described embodiments, the insertion hole formed at the presser portion of the lead connector is directed to substantially the same direction as the leads are drawn out of the housing of the electric motor (the direction of the through hole formed in the housing). The direction of the power cable lays in a plane perpendicular to the axial direction of the insertion hole which is substantially parallel to an upper surface of the housing of the electric motor. With this arrangement, the leads can be connected to the lead connectors and then fixed to the mounting portions of the terminal base without bending excessively or applying excessive force. The power cables can be connected with the power terminal mounting portions with an orientation substantially the same as the power cables are drawn along the surface of the housing. The terminal base is arranged offset to one side in the terminal box and the leads extend downwardly from the lead connector not to appear in the terminal box, a large space for connection of the power cables to the power terminal mounting portions is formed in the terminal box. The power cables can be easily connected to the power terminal mounting portions with a larger radius of curvature in the large space in the terminal box even if the power cables have large diameters. 
     According to the present invention, the space capable of being occupied by the power cables in connection of the power cable to the power terminal mounting portions is made larger so that a switching of windings of the stator for improving a performance of the electric motor is easily carried out. In manufacturing of the electric motor, the drawing and assembling of the leads are made easy. Further, the positions of the leads are fixed to make the inspection of the windings easy, to facilitate a full automatic assembling of the electric motor to lower the cost of manufacture.