Abstract:
A variable resistor for increased assembly efficiency and decreased influence by environmental changes is disclosed. The variable resistor includes a closed end main casing, an external terminal held in the main casing and connected to the insulating substrate, a side receiver movably held in the casing, a shaft for moving the slider receiver, and a cover for closing an opening of the casing. The shaft is supported by a bearing formed on the cover to protrude from the cover and is further provided with a fall-preventive means. The terminal and substrate are both connected on the opening side of the casing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electric part for use as, for example, a valve opening control sensor for an exhaust gas recirculator in a vehicle, a sensor for controlling the mixture ratio between gasoline and air, and various kinds of encoders. 
     2. Description of the Related Art 
     A conventional electric part of this type will be described with reference to a cross-sectional view of FIG.  13 . The electric part shown in FIG. 13 comprises a casing  1  which forms an outer shell, a shaft  2  movable from side to side in FIG. 13 with respect to the casing  1 , an insulating substrate  3  housed in the casing  1 , a brush  4  which slidably contacts a conductive pattern (not shown), such as a resistor or a current collector, provided on the insulating substrate  3 , a slider receiver  5  for holding the brush  4 , a return spring  6  positioned offset from the axis of the shaft  2  to supply a spring force to the slider receiver  5 , and an external terminal  7  connected to the insulating substrate  3 . 
     In the casing  1 , the shaft  2  is inserted into a slot  1   a  provided at one end of the casing  1 , and an opening  1   b  at the other end is tightly sealed with a cover  8 . A pair of guide grooves (not shown), extending parallel to the axis of the shaft  2 , are formed on opposed inner walls of the casing  1 , and a pair of projections  5   a  formed on the slider receiver  5  are engaged with the guide grooves. 
     The insulating substrate  3  housed in the casing  1  is engaged, at both side ends thereof, with a second pair of grooves formed on the opposed inner walls of the casing  1 , and urged toward the slider receiver  5  by a corrugated leaf spring  9  interposed between the casing  1  and the back of the insulating substrate  3 . 
     At one end of the insulating substrate  3 , a terminal section  3   a  having thereon a conductive terminal pattern (not shown) connected to the resistor or the current collector is formed. A connecting section  7   a  is formed at one end of the external terminal  7 . The terminal section  3   a  of the insulating substrate  3  and the connecting section  7   a  of the external terminal  7  are connected to each other by a clip terminal  10  on the side of the opening  1   b  of the casing  1 . Furthermore, a groove  11  for holding the return spring  6  is formed at the position offset from the axis of the shaft  2  in the casing  1 , and the return spring  6  held in the groove  11  urges the slider receiver  5  in the axial direction. The shaft  2  and the slider receiver  5  are provided with a convex section  2   a  and a concave section  5   b , respectively, which are engaged with each other. A hole  1   c  is formed for use in attaching this electric part to other devices. 
     The conventional electric part having the above-mentioned construction is assembled as follows: First, the leaf spring  9  and the insulating substrate  3  are loaded in the casing  1 . Next, the shaft  2  is inserted into the slot  1   a , which is formed at the other side of the opening  1   b  of the casing  1 , from the side of the opening  1   b , the pair of projections  5   a  of the slider receiver  5  are engaged with the pair of grooves in the casing  1 , and the slider receiver  5  is engaged with the shaft  2 . Then, the terminal section  3   a  of the insulating substrate  3  and the connecting section  7   a  of the external terminal  7  are resiliently clamped by the clip terminal  10 , and the return spring  6  is inserted into the groove  11  for housing the spring in the casing  1 . Finally, the opening  1   b  of the casing  1  is closed by the cover  8 . 
     In the foregoing electric part, however, since the shaft  2  must be inserted into the slot  1   a  located on the side of the casing  1  which is far back from the opening  1   b , insertion is difficult, and assembly efficiency is thereby reduced. 
     The electric part constructed as mentioned above is, for example, attached to a control valve container  12 , as a valve opening detecting sensor for use in an exhaust gas recirculator in an engine, through an attachment member  13  or the like, as shown in FIG.  14 . The electric part is so attached that the shaft  2  projects into the control valve container  12  and that hermetic sealing is provided between the electric part and the control valve container  12 . The shaft  2  moves inward and outward in correlation to the motion of a control valve (not shown) in the control valve container  12 . 
     In such a state in which the electric part is attached to the control valve container  12 , the cover  8  covering the opening  1   b  of the casing  1  is exposed outside. Therefore, even if the opening  1   b  of the casing  1  is tightly sealed with the cover  8 , the sealing state is deteriorated under the influence of long-term changes in the external environment, such as temperature and humidity, dust or the like, whereby the contact between the brush  4  in the casing  1  and the resistor and the current collector on the insulating substrate  3  is made unstable. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an electric part which is excellent in assembly efficiency and is not influenced by environmental changes. 
     In order to achieve the above object, the present invention provides an electric part comprising a closed-end main casing, an insulating substrate held in the casing, an external terminal held in the main casing and connected to the insulating substrate, a slider receiver movably held in the casing, a shaft for moving the slider receiver, and a cover for closing an opening of the casing, wherein the shaft is supported by a bearing formed on the cover to protrude from the cover and further provided with a fall-preventive means, the insulating substrate has a terminal section at one end thereof, the outer terminal has a connecting section at one end thereof, and the terminal section and the connecting section are projected toward the opening of the casing and connected to each other by a clip terminal. 
     Furthermore, the cover is provided with a through hole, and the terminal section of the insulating substrate and the connecting section of the external terminal protrude outward through the through hole and are connected to each other. 
     Still furthermore, a protective cover for covering the terminal section of the insulating substrate and the connecting section of the external terminal is provided on the cover. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view of an electric part according to a first embodiment of the present invention. 
     FIG. 2 is a front view showing the inside of a casing of the electric part in the first embodiment. 
     FIG. 3 is a side view showing the contact state between an insulating substrate and an external terminal in the electric part of the first embodiment. 
     FIG. 4 is a plan view of a connecting section of the external terminal in the electric part of the first embodiment. 
     FIG. 5 is a plan view of a connecting section of the external terminal in the electric part of the first embodiment. 
     FIG. 6 is a cross-sectional view taken along line VI—VI of FIG.  3 . 
     FIG. 7 is a plan view of a connecting section of the external terminal in the electric part of the first embodiment. 
     FIG. 8 is a cross-sectional view taken along line VIII—VIII of FIG.  7 . 
     FIG. 9 is a longitudinal sectional view of an electric part according to a second embodiment of the present invention. 
     FIG. 10 is a perspective view of a cover to be used in the electric part of the second embodiment. 
     FIG. 11 is a longitudinal sectional view of an electric part according to a third embodiment of the present invention. 
     FIG. 12 is a perspective view of a cover to be used in the electric part of the third embodiment. 
     FIG. 13 is a longitudinal sectional view of a conventional electric part. 
     FIG. 14 is a view explaining the case of use of the conventional electric part. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An electric part according to a first embodiment of the present invention will be described with reference to FIGS. 1 to  8 . FIG. 1 is a longitudinal sectional view of an electric part of the first embodiment, which is taken in the axial direction of a shaft, FIG. 2 is a front view showing the inside of a casing shown in FIG. 1, FIG. 3 is a side view showing the contact state between an insulating substrate and an external terminal, FIGS. 4 and 5 are plan views of the external terminal, FIG. 6 is a cross-sectional view taken along line VI—VI of FIG. 3, FIG. 7 is a plan view of the external terminal, and FIG. 8 is a cross-sectional view taken along line VIII—VIII of FIG.  7 . 
     As shown in FIGS. 1 and 2, the electric part of the present invention mainly comprises a closed-end casing  21 , a cover  23  for closing an opening  22  of the casing  21 , an insulating substrate  24  housed in the casing  21 , a shaft  25 , a slider receiver  26  retained by the shaft  25  and being movable in the axial direction of the shaft  25  in the casing  21 , a return spring  27  for urging the slider receiver  26  in the axial direction, and an external terminal  28  held in the casing  21 . 
     The casing  21  is made of synthetic resin or the like. A pair of stoppers  30  for limiting the movement of the slider receiver  26  are projected from an end section  29  of the casing  21 , and a pair of projections  31  are formed to position the insulating substrate  24 . Furthermore, two pairs of opposed grooves  32  and  33  and a housing groove  34  for housing the return spring  27  therein are formed on the inner wall of the casing  21  as shown in FIG.  2 . 
     A cylindrical bearing  35 , through which the shaft  25  is inserted, is formed at about the midpoint of the cover  23  to extend inward of the casing  21 . The cover  23  is fitted in the inner wall of the casing  21  near the opening  22  thereof, thereby closing the opening  22 . 
     The insulating substrate  24  to be housed in the casing  21  is provided with a resistor and a current collector (both are not shown) on the upper surface thereof, and a terminal section  36  having a conductive terminal pattern (not shown) connected to the resistor and the current collector at one end thereof. Both side ends of the insulating substrate  24  are inserted in the pair of grooves  32  in the casing  21  shown in FIG. 2, and the other end thereof is held in contact with the positioning projections  31 . Furthermore, the insulating substrate  24  is urged toward the slider receiver  26  (upward) by a corrugated leaf spring  37  interposed between the back of the insulating substrate  24  and the inner wall of the casing  21 , and is thereby prevented from rattling in the vertical direction. In this state, the terminal section  36  of the insulating substrate  24  projects toward the opening  22  of the casing  21 . 
     The shaft  25  to be inserted through the bearing  35  of the cover  23  is provided with a large-diameter section  25   a  as a fall-preventive means, and a convex section  38  formed at the leading end of the large-diameter section  25   a . On the other hand, the slider receiver  26  is provided with a concave section  39  opposed to the convex section  38  and having a large diameter than the convex section  38 . The convex section  38  is engaged with the concave section  39 . The slider receiver  26  is further provided with a head section  40  projecting into the spring housing groove  34  in the casing  21 , a pair of engaging projections  41  formed on the right and left sides in the moving direction of the slider receiver  26  to be engaged with the pair of grooves  33  in the casing  21 , and a slider  42  for sliding over the resistor and the current collector on the insulating substrate  24 . The slide receiver  26  is moved against the urging force of the return spring  27  by the pressing force applied to the shaft  25  from outside. 
     The external terminal  28  is held in the casing  21  by means of insert molding or the like. The external terminal  28  is provided with a connecting section  43  at one end to project parallel to the terminal section  36  of the insulating substrate  24  toward the opening  22 , and the other end thereof is bent and projected sideward from the casing  21 . The terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  are connected to each other by a connecting means such as a clip terminal  44 . Accordingly, the connection is easily achieved only by resiliently clamping the terminal section  36  and the connecting section  43  with the clip terminal  44 . 
     The clip terminal  44  is, as shown in FIG. 3, composed of two clip sections  45  and  46  for resiliently clamping the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28 , and a linking section  47  for linking the clip sections  45  and  46 . The connecting section  43  of the external terminal  28  to be resiliently clamped by the clip section  46  is provided with a cutout groove  48  as shown in FIG. 4 or  5 . On the other hand, the clip section  46  is provided with a bent section  49  which is V-shaped in cross section. As shown in FIG. 6, the bent section  49  is engaged with the cutout groove  48 , whereby the connecting section  43  is resiliently clamped by the clip section  46 . The connecting section  43  may be provided with a concave groove  50  shown in FIGS. 7 and 8 instead of the cutout groove  48  shown in FIGS. 4 and 5. 
     Since the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  43  are thus connected by the clip terminal  44 , it is only necessary to insert and engage the bent section  49  of the clip terminal  44  with the cutout groove  48  or the concave groove  50  formed on the connecting section  43  of the external terminal  28 , and the connecting operation is easy. Such engagement of the cutout groove  48  or the concave groove  50  formed on the connecting section  43  of the external terminal  28  with the V-shaped bent section  49  of the clip section  46  of the clip terminal  44  enhances reliability of connection. 
     The electric part of the present invention having the foregoing construction is assembled as follows. First, the insulating substrate  24  is inserted together with the leaf spring  37  into the casing  21  holding the external terminal  28  while both side ends thereof are engaged with the grooves  32 , and brought into contact with the positioning projections  31 . The return spring  27  is inserted in the spring housing section  34 . Next, the slider receiver  26  is inserted into the casing  21  while the pair of engaging projections  41  thereof are engaged with the pair of grooves  33  in the casing  21 . Then, the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  are resiliently clamped by the two clip sections  45  and  46  of the clip terminal  44  as a connecting means. 
     In this case, the slider receiver  26  is pressed back toward the opening  22  of the casing  21  by the return spring  27  to such an extent that the return spring  27  stretches to its full length. As a result, the leading end of the slider  42  retained by the pressed slider receiver  26  is brought near the terminal section  36  of the insulating substrate  24  and positioned at a desired distance from the clip terminal  44 . In this state, the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  are connected by the clip terminal  44 . Next, the shaft  25  is engaged with the slider receiver  26 , and the opening  22  of the casing  21  is closed by the cover  23 . At this time, if the shaft  25  is inserted in the bearing  35  of the cover  23  beforehand, the convex section  38  of the shaft  25  can be engaged with the concave section  39  of the slider receiver  26  by fitting the cover  23  in the opening  22  of the casing  21 . The shaft  25  is prevented from falling off by the fall-preventive means  25   a . At the same time, the spring  27  is slightly compressed. 
     As mentioned above, the electric part according to the first embodiment of the present invention has high assembly efficiency because the shaft  25  can be inserted in the casing  21  and engaged with the slider receiver  26  only by fitting the cover  23  in the opening  22  of the casing  21 . Furthermore, since the shaft  25  moves in and out of the cover  23  closing the opening  22  of the casing  21 , when the electric part is attached, as a sensor, to a control valve container in an exhaust gas recirculator of an engine or the like, the components of the electric part on the side of the opening  22  including the shaft  25  are sealed in the container and only the end section  29  of the casing  21  is exposed outside. Consequently, contact failure of the slider  42  and the clip terminal  44  is prevented from being caused by changes in the environment such as external humidity. 
     In the first embodiment, if the shaft  25  and the slider receiver  26  are integrally formed, the cover  23  can be fitted in the casing  21  after simultaneously inserting the shaft  25  and the slider receiver  26  into the casing  21 . In this case, since the shaft  25  and the slider receiver  26  formed integrally can be simultaneously inserted into the casing  21 , the assembly operation is facilitated. 
     Next, a second embodiment of the present invention will be described with reference to FIGS. 9 and 10. FIG. 9 is a side sectional view of an electric part according to the second embodiment of the present invention, and FIG. 10 is a perspective view of a cover to be used in the electric part shown in FIG.  9 . Components which are the same as in the electric part of the first embodiment are given the same reference numerals, and the description thereof is omitted. 
     The electric part of the second embodiment is different from the first embodiment in having a cover  61 . Other components, a casing  21 , an insulating substrate  24 , a shaft  25 , a slider receiver  26 , a return spring  27 , an external terminal  28 , a leaf spring  37 , a slider  42  and a clip terminal  44  are the same as those in the electric part of the first embodiment. 
     The cover  61  for closing an opening  22  of the casing  21  has an almost concave shape as shown in FIGS. 9 and 10, and a cylindrical bearing  63  projecting outward and inward the casing  21  is formed at about the midpoint of a concave bottom  62  thereof. A slit  64  through which a terminal section  36  of the insulating substrate  24  is inserted, and three slits  65  through which a connecting section  43  of the external terminal  28  is inserted are formed in parallel on the bottom  62 . 
     The electric part of the second embodiment which has the foregoing cover  61  is assembled as follows. First, the insulating substrate  24  is inserted together with the leaf spring  37  into the casing  21  holding the external terminal  28  while both side ends thereof are engaged with grooves  32 , and brought into contact with positioning projections  31 . The return spring  27  is inserted in a spring housing section  34 . Next, the slider receiver  26  is inserted into the casing  21  while a pair of engaging projections  41  thereof are engaged with a pair of grooves  33  in the casing  21 . 
     Though these assembly steps are the same as those of the electric part of the first embodiment, in the second embodiment, the cover  61  having the shaft  25  inserted through the bearing  63  beforehand is next fitted in the opening  22  of the casing  21 , thereby closing the opening  22 . Then, the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  are resiliently clamped by the clip terminal  44 . In other words, when the cover  61  is fitted in the casing opening  22 , the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  are respectively inserted into the slits  64  and  65  formed on the bottom  62  of the cover  61  and projected outward. Next, these projecting terminal section  36  and connecting section  43  are resiliently clamped by the clip terminal  44  and connected to each other. 
     As mentioned above, in the second embodiment, since the cover  61  is fitted in the casing  21  before the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  are resiliently clamped by the clip terminal  44 , the slider receiver  26  retained by the shaft  25  is held in the casing  21 . Only the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  project from the cover  61 , and therefore, it is easy to make the clip terminal  44  resiliently clamp the terminal section  36  and the connecting section  43 . In the second embodiment, if the shaft  25  and the slider receiver  26  are integrally formed, the slider receiver  26  can be inserted into the casing  21  upon fitting the cover  61  in the opening  22  of the casing  21 , which makes the assembly operation simpler. In the first embodiment, the clip terminal  44  is required to be mounted without any contact with the slider  42 , and therefore, the insulating substrate  24  is required to extend in the lengthwise direction of the external terminal  28  so as to have the length including the full length of the return spring  27  and an additive allowance. However, in the second embodiment, the slider receiver  26  can place the return spring  27  into a compressed position in mounting the clip terminal  44 , whereby the slider receiver  26  can be placed at a farther position inside the casing  21 . As a result, the insulating substrate  24  can be shortened. 
     Next, a third embodiment of the present invention will be described with reference to FIGS. 11 and 12. FIG. 11 is a side sectional view of an electric part according to the third embodiment of the present invention, and FIG. 12 is a perspective view of a cover to be used in the electric part shown in FIG.  11 . In these figures, components which are the same as in the electric part of the first embodiment are given the same reference numerals, and the description thereof will be omitted. 
     The electric part of the third embodiment is different from the second embodiment in having a cover  71 . Other components, a casing  21 , an insulating substrate  24 , a shaft  25 , a slider receiver  26 , a return spring  27 , an external terminal  28 , a leaf spring  37 , a slider  42  and a clip terminal  44  are the same as those in the electric part of the second embodiment. 
     The cover  71  for closing the opening  22  of the casing  21  has an almost concave shape as shown in FIGS. 11 and 12, and a cylindrical bearing  73  projecting outward and inward the casing  21  is formed at about the midpoint of a concave bottom  72  thereof. The bottom  72  is further provided with a divider wall  74  formed integrally with the bearing  73  and projecting outward, a slit  75  through which a terminal section  36  of the insulating substrate  24  is inserted, and three slits  76  through which a connecting section  43  of the external terminal  28  is inserted. These slits are formed in parallel. Furthermore, the cover  71  has a protective cover  77  integrally formed therewith through hinges  78 . 
     The electric part of the third embodiment having the foregoing cover  71  is assembled just the same as the electric part of the second embodiment. In other words, the insulating substrate  24  is inserted together with the leaf spring  37  into the casing  21  holding the external terminal  28 , and the return spring  27  is inserted in a spring housing section  34 . Next, the slider receiver  26  is inserted into the casing  21 . 
     Then, the cover  71  having the shaft  25  inserted through the bearing  73  beforehand is fitted in the opening  22  of the casing  21 , and then, a convex section  38  of the shaft  25  is engaged with a concave section  39  of the slider receiver  26 . The terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  are respectively inserted into the slits  75  and  76  formed on the bottom  72  of the cover  71  and projected outward, and then, connected to each other by being resiliently clamped by the clip terminal  44 . Finally, the protective cover  77  is fitted on the bearing  73 , thereby covering the clip terminal  44 . The protective cover  77  may be a separate piece. In the third embodiment, if the shaft  25  and the slider receiver  26  are integrally formed, the slider receiver  26  can be inserted in the casing  21  upon fitting the cover  71  in the opening  22  of the casing  21 , which facilitates the assembly operation. 
     As mentioned above, since the protective cover  77  covers the clip terminal  44 , the ingress of dirt and dust is prevented, which achieves more reliable contact between the clip terminal  44 , and the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28 . 
     According to the present invention, as mentioned above, since the cover is provided with the bearing for supporting the shaft having a fall-preventive means, the shaft can be engaged with a slider receiver and inserted in the casing by fitting the cover in the opening of the casing, which enhances assembly efficiency. Furthermore, since the shaft moves in and out of the cover for closing the opening of the casing, when the electric part is attached, as a sensor, to a control valve container in an exhaust gas recirculator of an engine or the like, the components of the electric part on the side of the opening including the shaft are sealed in the housing and only the end section of the casing is exposed outside the housing. Consequently, contact failure of the slider and the clip terminal is prevented from being caused by changes in the environment such as external humidity. 
     The insulating substrate is provided with a terminal section at one end thereof, the outer terminal is provided with a connecting section at one end thereof, and the terminal section and the connecting section are projected from the opening of the casing and connected to each other only by being resiliently clamped by a clip terminal. 
     Furthermore, the cover is provided with slits, and the terminal section of the insulating substrate and the connecting section of the external terminal are protruded outward through the slits and connected to each other. Since only the terminal section and the connecting section protrude from the cover, the clamping thereof by means of the clip terminal is easy to perform. 
     Still furthermore, a protective cover is provided on the cover to cover the terminal section of the insulating substrate and the connecting section of the external terminal. Accordingly, the ingress of dirt and dust is prevented, and reliability of the contact between the clip terminal  44 , and the terminal section  36  of the insulating substrate  24  and the connecting section  43  of the external terminal  28  is enhanced.