Patent Publication Number: US-2019190186-A1

Title: Connector structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 USC 119 from Japanese Patent Application No. JP 2017-241924 filed on Dec. 18, 2017, the disclosure of which is incorporated by reference herein. 
     TECHNICAL FIELD 
     The present invention relates to a connector structure. 
     BACKGROUND 
     An electronic component of a switch or the like that is mounted on a vehicle is connected electrically to a battery, a control device and the like at a vehicle side using a connector (for example, refer to WO2017/032638). 
       FIG. 7  is a diagram explaining the assembling of a switch provided with a conventional connector structure. 
     As illustrated in  FIG. 7 , an electronic component is provided with an electronic substrate  700  and a case  100 . The case  100  is provided with a case body  110  for accommodating the electronic substrate  700  therein and a cover  150  for closing an opening of the case body  110 . A connector  500  at the electronic component side is provided with a terminal part  510  supporting a plurality of terminals and a tubular housing  550  surrounding tip end sides of the plurality of terminals. A connector (unillustrated) at a vehicle side is inserted from an opened tip end side of the housing, and is connected to a connector at the electronic component side. 
     The terminal part  510  of the connector  500  and the housing  550  are usually formed integrally, but a separate formation of the terminal part  510  and the housing  550  has been proposed for cutting down on manufacturing costs. In the example in  FIG. 7 , the terminal part  510  and the housing  550  are formed separately and the housing  550  is formed to be integral with the case body  110 . The terminal part  510  is in advance fixed on the electronic substrate  700  by soldering or the like, and then the electronic substrate  700  is accommodated in the inside of the case body  110  from the opening of the case body  110 . The electronic substrate  700  and the case body  110  are positioned by respective positioning parts  110   a ,  700   a  to be mounted. The opening of the case body is covered with the cover  150 , preventing intrusion of dusts and the like. 
     In a case where the terminal part  510  of the connector  500  and the housing  550  are separately formed, since the terminal part  510  of the connector  500  and the housing  550  are positioned through the electronic substrate  700  and the case body  110  connected thereto respectively, each positional accuracy possibly gets lower as compared to a case of being integrally formed. When the positional accuracy of the terminal part  510  and the housing  550  is reduced, at the time of inserting the connector at the vehicle side from the tip end of the housing  550  to be connected to the terminal part  510  of the connector  500 , there is a possibility that required positional accuracy cannot be achieved. 
     For enhancing the positional accuracy of the terminal part  510  and the housing  550 , it is considered to cause the case body  110 , which has been positioned with respect to the electronic substrate  700 , to be positioned directly with respect to the terminal part  510 . However, in that case, there is a possibility that the positional accuracy of the case body  110  and the electronic substrate  700  is reduced to reduce positional accuracy of the electronic component of the switch or the like. 
     SUMMARY 
     Accordingly, the present invention is made in view of the above-described problems, and an object of the present invention is to provide a connector structure that prevents positional accuracy of a housing and a terminal part for a connector attached to a switch and positional accuracy of an electronic component from being reduced while reducing manufacturing costs of the switch. 
     According to an aspect of the present invention, a connector structure in a case in which a connector is attached comprises: 
     the case including: 
     a case body for accommodating an electronic substrate therein; and 
     a cover for closing an opening of the case body, wherein 
     the connector includes: 
     a terminal part for supporting a plurality of terminals; and 
     a housing including a tubular part for surrounding tip end sides of the plurality of terminals, 
     the terminal part and the housing are separately disposed, 
     the terminal part is fixed on the electronic substrate, 
     the housing is formed to be integral with the cover, and 
     the terminal part and the housing are respectively provided with positioning parts for positioning the terminal part and the housing with each other. 
     According to the aspect of the present invention, the terminal part and the housing for the connector are separately disposed, and the housing is not formed to be integral with the case body configuring a function of the electronic component, but is formed to be integral with the cover that covers the opening of the case body for protection from an outside environment. Further, the terminal part and the housing are respectively provided with the positioning parts for the positioning with each other. As a result, separately forming the terminal part and the housing enables a reduction in costs. Since it is possible to directly position the terminal part and the housing, a reduction in positional accuracy of the terminal part and the housing can be prevented to easily secure the positional accuracy required for connection to the connector at the vehicle side. Further, since the case body is not formed to be integral with the housing, the case body can be directly positioned with respect to the electronic substrate, making it possible to prevent the reduction in the positional accuracy of the electronic component, too. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features, and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which: 
         FIG. 1  is a perspective view illustrating the configuration of an outer appearance of a switch according to an embodiment in the present invention, 
         FIG. 2  is an exploded perspective view illustrating the switch according to the embodiment, 
         FIG. 3  is an exploded cross section illustrating the switch according to the embodiment, as viewed from a direction of Y axis of the switch, 
         FIG. 4  is a plan view illustrating a housing formed to be integral with a cover according to the embodiment, 
         FIG. 5A  is a perspective view illustrating a tubular part and an extension part of the switch in an assembled state of the switch according to the embodiment, 
         FIG. 5B  is a perspective view illustrating only the extension part of the switch in the assembled state of the switch according to the embodiment, 
         FIG. 6  is a cross section taken along Y axis of the switch and illustrating the assemble state of the switch according to the embodiment, and 
         FIG. 7  is a diagram explaining the assembling of a switch provided with a conventional connector structure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an explanation will be made of a connector structure in a case in which a connector is attached according to an embodiment in the present invention. The case configures an electronic component, and the electronic component is not limited to a specific component, and an explanation of the embodiment will be made using an example of a switch that is installed in a vehicle. 
       FIG. 1  is a perspective view illustrating an assembled state of a switch. 
       FIG. 2  is an exploded perspective view of the switch. 
       FIG. 3  is an exploded cross section illustrating the switch, as viewed from a direction of Y axis of the switch. However, in  FIG. 3 , illustration of a knob is omitted. 
     As illustrated in  FIG. 1  and  FIG. 2 , a switch as an electronic component is provided with a case  1  that accommodates therein an electronic substrate on which switch elements and the like are installed, and a knob  3  that is held in the case  1  and switches an on/off operation of the switch. A connector  5  is attached on the case  1  to connect the switch to a power source, a control device or the like installed at a vehicle side. An explanation of the embodiment will be made using an example where the connector  5  attached on the case  1  is a male connector. 
     The case  1  is provided with a boxy case body  11  a lower end of which is opened, and a plate-shaped cover  15  that closes a lower end opening  11   a  of the case body  11 . It should be noted that, for descriptive purposes, an upper side is defined as an upper direction and a lower side is defined as a lower direction in  FIG. 2 , and, based thereupon, a positional relation of the respective elements of the switch will be explained. In addition, an axis line along an assembling direction of the switch is defined as “axis line X” and an axis line in a direction perpendicular to the axis line X is defined as “axis line Y”. 
     The case body  11  and the cover  15  each are formed by molding or the like. The case body  11  accommodates the electronic substrate  7  therein and is fixed on an unillustrated vehicle body (fixed member). Although unillustrated, the electronic substrate  7  is provided thereon with various components configuring the electronic component, such as switching elements, LEDs and the like. A projection  12  that is a positioning part with respect to the electronic substrate  7  is formed on an inner upper surface  11   c  of the case body  11  (refer to  FIG. 3 ). In addition, the electronic substrate  7  is provided with a plurality of holes  71 ,  73  that are positioning parts with respect to other members including the case body  11 . 
     A holding part  13  of the knob  3  is disposed on an outer upper surface  11   b  of the case body  11 . The knob  3  is a tubular member an upper end of which is closed and a lower end of which is opened, and a pressing part  31  is disposed on its lower end. The pressing part  31  is formed in a position corresponding to the switching element installed on the electronic substrate  7 . 
     The knob  3  is held in the holding part  13  of the case body  11 . By pressing down an upper end surface  3   a  of the knob  3 , the knob  3  slides toward the inside of the case body  11  to cause the pressing part  31  in the lower end of the knob  3  to press the switching element, thus switching an on/off operation of the switch. The switching element is provided with a resilient member of a rubber sheet or the like, and when the upper end surface  3   a  of the knob  3  is released, the knob  3  is urged by the resilient member to be returned back to an initial position. 
     The connector  5  is provided with a terminal part  51  for supporting a plurality of pin-shaped terminals  9  and a housing  55  for accommodating the terminal part  51  therein. The terminal part  51  and the housing  55  are separately formed, and the housing  55  is formed to be integral with the cover  15  by molding or the like. 
     The terminal part  51  is a rectangular terminal platform, and the plurality of pin-shaped terminals  9  arranged along the axis line Y are supported by penetration of them through side surfaces  51   a ,  51   a , which are opposed to each other, of the terminal part  51 . Projections  52 ,  52  are formed on an upper surface  51   c  of the terminal part  51  in the vicinity of both ends thereof in the axis line Y direction. The projection  52  is a positioning part with respect to the electronic substrate  7 . A through hole  53   a  and a groove  53   b  are respectively formed in the vicinities of the projections  52 ,  52 . The through hole  53   a  penetrates from the upper surface  51   c  over a lower surface  51   d  of the terminal part  51 . The groove  53   b  is formed on a side surface  51   b  connecting the side surfaces  51   a ,  51   a , and extends along the axis line X from the upper surface  51   c  to the lower surface  51   d . The through hole  53   a  and the groove  53   b  are positioning parts with the housing  55 . 
     As illustrated in  FIG. 3 , both ends of the plurality of pin-shaped terminals  9  each project from the side surfaces  51   a ,  51   a , which are opposed to each other, of the terminal part  51 , are bent at the right angle toward the upper surface  51   c  of the terminal part  51 , extend to a position of the upper surface  51   c  of the terminal part  51 , and thereafter, extend horizontally along the axis line Y. One horizontal part  91  extending horizontally along the axis line Y is longer than the other horizontal part  92 . In  FIG. 3 , as surrounded by circles, a base end section of each of the horizontal parts  91 ,  92  is earth-connected to the electronic substrate  7 . A tip end of the longer horizontal part  91  projects outward from an outer edge of the electronic substrate  7 , and a female connector is connected to this tip end. 
       FIG. 4  is a plan view illustrating the housing formed to be integral with the cover. 
     As illustrated in  FIG. 2  and  FIG. 4 , the cover  15  is provided with a rectangular flat surface part  16  that extends along the axis line Y to cover the lower end opening  11   a  of the case body  11 , and a peripheral wall  17  that is disposed to extend upward along the axis line X from an outer edge of the flat surface part  16  and extends to the case body  11 -side. A stage  18  is disposed on the flat surface part  16  to support the electronic substrate  7 . Part of the electronic substrate  7  is supported on the stage  18  and the rest extends on the flat surface part  16  to face the flat surface part  16  by an interval. 
     As illustrated in  FIG. 1 , in a state where the case body  11  and the cover  15  are assembled, the peripheral wall  17  of the cover  15  faces an inner side surface  11   d  of the case body  11  in the vicinity of the lower end opening  11   a . Since a dimension of the outer edge of the flat surface part  16  is set to be smaller than that of an outer edge of the lower end opening  11   a  of the case body  11 , the peripheral wall  17  of the cover  15  faces the inner side surface  11   d  of the case body  11  with a gap D 1  (refer to  FIG. 6 ). 
     A flange  20  is disposed to extend horizontally with respect to the flat surface part  16  over an entire circumference of the outer edge of the flat surface part  16  of the cover  15 . As illustrated in  FIG. 1 , the flange  20  covers the gap D 1  between the inner side surface  11   d  of the case body  11  and the peripheral wall  17  of the cover  15 . Since the flange  20  is only required to be as long as to cover the gap D 1 , the flange  20  may have the same dimension as an outer side surface  11   e  of the case body  11  or may be longer than that. 
     The housing  55  is provided with a support part  56  that supports the terminal part  51  and a tubular part  58  that surrounds a tip end side of the horizontal part  91  of the pin-shaped terminal  9 . 
     The support part  56  is a recessed part formed on the flat surface part  16  of the cover  15 , and the lower surface  51   d  of the terminal part  51  is placed and supported on the support part  56  (refer to  FIG. 6 ). The support part  56  is provided with projections  57   a ,  57   b  that are positioning parts with respect to the terminal part  51 . The projection  57   b  is formed in the form of swelling in the axis line Y direction from the peripheral wall  17  of the cover  15 . When the projection  57   a  is inserted in the through hole  53   a  of the terminal part  51  and the projection  57   b  is inserted in the groove  53   b , the terminal part  51  and the housing  55  are positioned. 
     As illustrated in  FIG. 2 , the tubular part  58  is formed to extend outward from the outer edge of the flat surface part  16  of the cover  15 . It should be noted that the peripheral wall  17  of the cover  15  and the flange  20  as described before are formed in sections other than the tubular part  58 . 
     A base end  58   a -side, which is in contact with the outer edge of the flat surface part  16 , of the tubular part  58  and a tip end  58   b -side, which opposes the base end  58   a , of the tubular part  58  are opened. A notch  59  is formed in the base end  58   a -side of the outer upper surface  58   c  of the tubular part  58 . At the time of assembling the terminal part  51  on the housing  55 , the tip end of the horizontal part  91  of the pin-shaped terminal  9  supported by the terminal part  51  is caused to be accommodated in the inside of the tubular part  58  through the notch  59  of the tubular part  58 . 
       FIG. 5A  is a perspective view illustrating the tubular part and the extension part in the assembling state of the switch, and  FIG. 5B  is a perspective view illustrating the extension part alone. 
     As illustrated in  FIG. 5A , the periphery of the tip end of the pin-shaped terminal  9  is surrounded by the tubular part  58 , but a terminal of the female connector is connectable from an exterior of the switch through the opened tip end  58   b  of the tubular part  58 . A guide  60  is formed on an inner lower part  58   d  of the tubular part  58  to guide the terminal of the female connector to the pin-shaped terminal  9 . 
     As described before, the case body  11  is formed in a boxy shape, but a section of the side surface, which faces the tubular part  58 , of the housing  55  extends outward along the tubular part  58  to form an extension part  14  covering the outer periphery of the tubular part  58 . The extension part  14  covers part of the exterior upper surface  58   c  and the exterior side surfaces  58   e ,  58   e  of the tubular part  58 , and is formed in a reverse-C letter shape as viewed in section. 
     A dimension of the outer periphery of the tubular part  59  of the connector  5  is made smaller than a dimension of an inner periphery of the extension part  14 . Therefore the extension part  14  covers the tubular part  58  through a gap D 2 . As illustrated in  FIG. 5B , a plurality of ribs  21  are formed on an inner upper surface  14   a  and an inner side surface  14   b  configuring the inner periphery of the extension part  14 . As illustrated in  FIG. 5A , these ribs  21  respectively extend in the gap D 2  to come in contact with the tubular part  58 . A convex part  22  is formed on the inner upper surface  14   a  of the extension part  14  facing the outer upper surface  58   c  of the tubular part  58  to be fitted in the notch  59  (refer to  FIG. 2 ) of the tubular part  58 . 
     An explanation will be made of the assembling and the operation of the switch having the above-mentioned configuration. 
     As described before, the cover  15  and the housing  55  for the connector  5  are formed to be integral by molding or the like, and then, the terminal part  51  of the connector  5 , the electronic substrate  7  and the case body  11  are assembled thereto. It should be noted that the knob  3  is held by the holding part  13  of the case body  11 , but the details thereof are omitted. 
     As illustrated in  FIG. 3 , the terminal part  51  of the connector  5  is fixed on the electronic substrate  7  before assembling the entire switch. The projection  52  formed on the upper surface  51   c  of the terminal part  51  is inserted in a hole  71  of the electronic substrate  7  for the positioning. 
     As illustrated by the round surroundings in  FIG. 3 , the base end sections of the horizontal parts  91 ,  92  of the pin-shaped terminal  9  are fixed on the electronic substrate  7  by soldering or the like. The tip end of the longer horizontal part  91  of the pin-shaped terminal  9  is placed to extend outward from the outer edge of the electronic substrate  7 . 
     Next, the electronic substrate  7  and the terminal part  51  that are fixed are assembled to the cover  15  and the housing  55  that are formed to be integral. 
       FIG. 6  is a cross section taken along a Y axis direction and illustrating the assembled state of the switch. In  FIG. 6 , the electronic substrate  7  is illustrated in a broken line for easy understanding. 
     As illustrated in  FIG. 3  and  FIG. 6 , the projections  57 ,  57  disposed in the support part  56  of the housing  55  are inserted in the through hole  53   a  and the groove  53   b  formed in the terminal part  51  for the positioning. The tip end of the pin-shaped terminal  9  supported in the terminal part  51  is accommodated in the inside of the tubular part  58  through the notch  59  of the tubular part  58 . Thereby the terminal part  51  and the electronic substrate  7  are assembled to the cover  15  formed to be integral with the housing  55 . 
     Subsequently the case body  11  will be assembled to the cover  15 . The projection  12  disposed on the inner upper surface  11   c  of the case body  11  is inserted in a hole  73  of the electronic substrate  7  to be positioned, and the convex part  22  formed on the inner upper surface  14   a  of the extension part  14  is fitted in the notch  59  formed in the outer upper surface  58   c  of the tubular part  58 . Thereby the flat surface part  16  of the cover  15  is assembled to cover the lower end opening  11   a  of the case body  11 . The extension part  14  of the case body  11  covers the tubular part  58  of the housing  55  formed to be integral with the cover  15 . 
     That is, in the embodiment the cover  15  and the case body  11  are not assembled to be directly positioned. The cover  15  and the case body  11  are assembled to be indirectly positioned in the form where the housing  55  of the connector  5  formed to be integral with the cover  15  and the terminal part  51  are positioned and the electronic substrate  7  in advance fixed in the terminal part  51  is positioned in the case body  11 . Therefore in a case where the cover  15  and the case body  11  are assembled without a gap, when the peripheral wall  17  of the cover  15  and the inner side surface  11   d  of the case body  11  have variations in dimension, there is a possibility that they interfere with each other to block the assembling thereof. Therefore the dimension of the peripheral wall  17  of the cover  15  is made smaller than the dimension of the inner side surface  11   d  of the case body  11  to cause the peripheral wall  17  of the cover  15  to face the inner side surface  11   d  of the case body  11  through the gap D 1 . Further, the flange  20  is disposed to extend outward from the outer edge of the cover  15 , and by covering the gap D 1  between the peripheral wall  17  and the inner side surface  11   d  of the case body  11  with the flange  20 , dusts can be prevented from entering the gap D 1 . 
     The inner periphery of the extension  14  of the case body  11  faces the outer periphery of the tubular part  58  with the gap D 2 , but as illustrated in  FIG. 5 , the plurality of ribs  21  disposed on the inner upper surface  14   a  and the inner side surface  14   b  of the extension part  14  extend in the gap D 2  to come in contact with the tubular part  58 , thus acting as gap fillings. When some of the plurality of ribs  21  do not come in contact with the extension  14  due to a dimension tolerance, a height of each of the ribs  21  is adjusted by a metallic mold. 
     When the female connector at the vehicle side is inserted from the tip end  58   b  of the tubular part  58  of the housing  55  in the connector  5  to be connected to the pin-shaped terminal  9  of the terminal part  51 , a prying force is applied on the housing  55 . When the prying force is input on the terminal part  51  connected to the housing  55  by the positioning to be applied on sections (sections surrounded by circles in  FIG. 3 ) of the terminal part  51  soldered to the electronic substrate  7 , a reduction in quality of the connector  5  is possibly invited. In the embodiment, since the tubular part  58  of the housing  55  is in contact with the ribs  21 , the prying force applied on the housing  55  tends to be easily scattered to the case body  11  fixed to the vehicle body through the ribs  21 , making it possible to reduce the prying force that will be input to the terminal part  51 . 
     It should be noted that, although not illustrated, a snap fit or the like may be disposed to the cover  15  and the case body  11  to fix the cover  15  to the case body  11 . 
     As described above, the connector structure according to the embodiment is the connector structure in the case  1  in which the connector  5  is attached, wherein, 
     the case  1  includes: 
     the case body  11  for accommodating the electronic substrate  7  therein; and 
     the cover  15  for closing the lower end opening  11   a  (opening) of the case body  11 , 
     the connector  5  includes: 
     the terminal part  51  for supporting the plurality of terminals  9  (terminals); and 
     the housing  55  including the tubular part  58  for surrounding tip end sides of the plurality of terminals  9 , 
     the terminal part  51  and the housing  55  are separately disposed, 
     the terminal part  51  is fixed on the electronic substrate  7 , 
     the housing  55  is formed to be integral with the cover  15 , and 
     the terminal part  51  and the housing  55  are respectively provided with the through hole  53   a  and the groove  53   b , and the projections  57 ,  57  (positioning parts) for positioning the terminal part  51  and the housing  55  with each other. 
     According to the conventional connector structure (refer to  FIG. 7 ), the housing  550  of the connector  500  is formed to be integral with the case body  110 . On assembling, the housing  550  and the terminal part  510  are indirectly positioned through the case body  110  and the electronic substrate  700  respectively connected thereto. As compared to a case where the housing  550  and the terminal part  510  are integrally formed, the cost can be reduced, but on assembling the whole, the positional accuracy of each possibly reduces. When the positional accuracy of the housing  550  and the terminal part  510  reduces, at the time the female connector at the vehicle side is inserted from the tip end of the tubular part of the housing  550  to be connected to the pin-shaped terminal, the positional accuracy required cannot be possibly achieved. 
     For enhancing the positional accuracy of the terminal part  510  and the housing  550 , it is considered to cause the case body  110 , which has been positioned with respect to the electronic substrate  700 , to be positioned directly with respect to the terminal part  510 . However, in that case, there is a possibility that the positional accuracy of the case body  110  and the electronic substrate  700  is reduced to reduce positional accuracy of the electronic component of the switch or the like. 
     In the connector structure according to the embodiment illustrated in  FIG. 1  to  FIG. 6 , the housing  55  of the connector  5  is not formed to be integral with the case body  11  configuring the function of the switch as the electronic component, but is formed to be integral with the cover  15  that covers the lower end opening  11   a  of the case body  11  for protection from the outside environment, thus directly positioning the terminal part  51  and the housing  55 . Thereby the terminal part  51  and the housing  55  are separately formed to reduce the cost while being capable of preventing the reduction in positional accuracy of the terminal part  51  and the housing  55 . Thereby the positional accuracy required in the connection to the connector  5  at the vehicle side is more likely to be secured. Further, since the case body  11  is not formed to be integral with the housing  55 , the case body  11  can be directly positioned with respect to the electronic substrate  7 , also preventing a reduction in positional accuracy of the electronic component. 
     It should be noted that in the embodiment, the example of using the through hole  53   a  and the terminal part  51  and the groove  53   b , and the projections  57 ,  57  as the positioning parts of the terminal part  51  and the housing  55  is explained, but the positioning part is only required to be capable of positioning the respective members with respect to each other, and the configuration and the disposed position can be changed as needed. Also as to the positioning part of the other member, the configuration and the disposed position are not limited to specific ones. 
     (2) The case body  11  is fixed on the vehicle body (fixed member) and is provided with the extension part  14  for covering at least part of the outer periphery of the tubular part  58  of the housing  55 , and the inner upper surface  11   c  and the inner side surface  11   d  (inner periphery), which face the outer periphery of the housing  55  through the gap D 2 , of the extension part  14  are provided with the ribs  21  (projections) in contact with the outer periphery of the tubular part  58  of the housing  55 . 
     When the female connector at the vehicle side is inserted from the tip end of the tubular part  58  of the housing  55  of the connector  5  to be connected to the pin-shaped terminal  9  of the terminal part  51 , the prying force is applied on the housing  55 , but the tubular part  58  of the housing  55  comes in contact with the ribs  21  to act as the gap fillings. Thereby the prying force applied to the housing  55  tends to be easily scattered to the case body  11  fixed on the vehicle body through the ribs  21 . Thereby it is possible to reduce the prying force that is input to the terminal part  51  to be applied to the section of the terminal part  51  and the electronic substrate  7  fixed by soldering, making it possible to prevent the reduction in quality of the connector  5 . In addition, when some of the ribs  21  do not come in contact with the outer periphery of the extension part  14  due to the dimension tolerance, the height of each of the ribs  21  can be adjusted by the metallic molding. 
     It should be noted that in the embodiment, the example of disposing the ribs  21  on the inner periphery of the extension part  14  is explained as an example of the projection, but the projection is not limited to this example. The projection is only required to project from somewhere of the inner periphery of the extension part  14  or the outer periphery of the tubular part  58  to cause the inner periphery of the extension part  14  to come in contact with the outer periphery of the tubular part  58 . For example, a projection in a semispherical shape may be disposed as the projection. In addition, the projection is not disposed on the inner peripheral side of the extension part  14 , but may be disposed on the outer peripheral side of the tubular part  58 . 
     (3) The cover  15  is provided with the flat surface part  16  that covers the lower end opening  11   a  of the case body  11 , the peripheral wall  17  that extends to the case body  11 -side from the outer edge of the flat surface part  16  and faces the inner side surface  11   d  (inner periphery) of the case body  11  with the gap D 1 , and the flange  20  that is disposed over the entire circumference of the outer edge of the flat surface part  16  and extends in the horizontal direction with respect to the flat surface part  16  to cover the gap D 1  between the inner side surface  11   d  of the case body  11  and the peripheral wall  17  of the cover  15 . 
     In the embodiment the cover  15  and the case body  11  are not directly positioned. Therefore in a case where the cover  15  and the case body  11  are to be assembled without a gap, when the peripheral wall  17  disposed to rise in the upward direction from the outer edge of the cover  15  and the inner side surface  11   d  of the case body  11  have variations in dimension, there is a possibility that the cover  15  and the case body  11  interfere with each other to block the assembling thereof. Therefore the gap D 1  is provided between the peripheral wall  17  of the cover  15  and the inner side surface  11   d  of the case body  11  to prevent the interference between the cover  15  and the case body  11 . Further, the flange  20  is disposed to extend outward from the outer edge of the cover  15 , and by covering the gap D 1  between the peripheral wall  17  and inner side surface  11   d  of the case body  11  with the flange  20 , dusts can be prevented from entering the gap D 1 . 
     While only the selected embodiment has been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiment according to the present invention is provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.