Bulb socket

Abstract: A projection (10c) is provided on a negative terminal (10) projecting toward the socket center and positioned directly below the bottom (13s) of the bulb base (13a), a cut-out recessed (10f) to the bottom is provided in the top of the base part (10e), which is positioned along the bottom of the bulb insertion opening (1a) and is bent in the perpendicular horizontal direction from the bottom of the flat member (10a), and the base part (10e) is set to not contact the positive terminal (11) when positioned with the projection (10c) contacting the bottom shoulder (13s) of the bulb base (13a).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bulb socket for use mainly in automotive lights and, more particularly, to a bulb socket for a bulb of the kind having two filaments each connected to positive and negative terminals provided inside the bulb socket. The present invention has been made to provide a bulb socket with improved negative and positive terminals so as to prevent the negative terminal from short-circuiting with the positive terminal even when the negative terminal moves away from the normal position in the socket. 2. Description of the Prior Art In Figs. 5 and 6, a conventional bulb socket for housing a single-filament bulb having one filament is shown. A negative terminal 2 and positive terminal 3 are provided by insertion to the bulb socket 1 (Fig. 5). A bulb 4, indicated by an imaginary line in Fig. 6, is inserted into a bulb insertion opening 1a of the bulb socket 1. A bulb-side contacting element 2a of the negative terminal 2 contacts a negative electrode on the outside circumference of a bulb base 4a. A bulb-side contacting element 3a of the positive terminal 3 contacts a positive electrode 4b of the bulb base 4a. A connector element 2b of the negative terminal 2 and a connector element of the positive terminal 3 project into a connector insertion part 1b of the bulb socket 1, in which each of connector elements are connected with external connectors (not shown) inserted into the connector insertion part 1b. The positive terminal 3 is securely held in the bulb socket 1 because the bulb-side contacting element 3a is pressed from above by the bulb 4. Because the negative terminal 2 is held in the socket 1 only by an engaging piece 2c engaged with a lock channel 1c of the bulb socket 1, it is not securely locked. And because the engaging piece 2c is often extremely small and has no engaging margin, the negative terminal 2 is not securely locked in some cases. In particular, when installed in a motor vehicle and subjected to vibrations, etc., for extended periods of time, the engaging piece 2c easily disengages. When the engaging piece 2c disengages and removes from an insertion hole 1d, a base part 2d of the negative terminal 2 contacts the curved contacting element 3a of the positive terminal 3 positioned thereabove at an encircled area X in Fig. 6. In Fig. 7, other conventional negative terminal proposed in Japanese Utility Model Laid-open Publication (unexamined) No. H4-136890 issued December 21, 1992 is shown. In Fig. 8A, the conventional bulb socket 2 viewed at another angle than in Fig. 6 is shown. This negative terminal 2 comprises a projection 2f projecting from the flat member below the bulb-side contacting element 2a. The projection 2f projects inside of the bulb insertion opening 1a when the negative terminal 2 is installed in the bulb socket 1. When the engaging piece 2c disengages from the lock channel 1c, the negative terminal 2 comes out of the insertion hole ld and moves toward the bulb-side contacting element 3a located thereabove. Before the top of a base part 2d of the negative terminal 2 contacts the contacting element 3a at a position on a dot line L, the front edge 2s of projection 2f abuts on the shoulder of bulb base 4a, so that the negative terminal 2 is stopped thereat so as not to contact with the positive terminal 3. Thus, the short-cutting of the negative terminal 2 with the positive terminal 3 is prevented. In Fig. 8B, a relationship of the gap between the negative terminal 2 and the positive terminal is shown. In the case of a single bulb shown in Fig. 5, the base part 2d of the negative terminal 2 is positioned at the bottom side of the bulb-side contacting element 3a of the positive terminal 3, and there is a large gap G2 between the base part 2d and the contact point P of the bulb-side connector 3a directly above. Because there is a large gap G2 with a single bulb, and said gap G2 is larger than the gap between the bottom of the bulb base 4a and the projection 2f of the negative terminal 2 in the normal engagement position, the projection 2f is always stopped by the bulb base 4a before the base part 2d of the negative terminal 2 contacts the contacting element 3a of the positive terminal 3, preventing short-circuiting. As described above, when a single-filament bulb 4 is installed in the bulb socket 1 provided with a single positive terminal 3 and a single negative terminal 2, the negative terminal 2 shaped as described above is kept from contacting with the positive terminal 3. However, in the case of the bulb socket 1 which is used for housing a double-filament bulb 4 having two filaments, two positive terminals 3 and one negative terminal 2 are provided therein, as shown in Figs. 9 and 10A. Specifically, the negative terminal 2 is positioned under the one of the bulb-side contacting elements 3a positioned parallel to each other on the bottom side of the bulb insertion opening 1a. In other words, since the bottom of the bulb-side contacting element 3a is positioned directly above the base part 2d, it is impossible to form a gap G1 having a greater clearance between the base part 2d and a contact point P on the bottom surface of bulb-side contacting element 3a. As a result, the gap G1 is smaller than the gap G6 formed between the bottom of bulb base 4a and the projection of the negative terminal 2f, as best shown in Fig. 10A. In Fig. 10B, the relationship of the gaps formed among the negative terminal 2, positive terminal 3, and bulb base 4a inside the thus formed bulb socket 2 is shown. Since the gap G1 is smaller than the gap G6, the base part 2d contacts with the contact point P of bulb-side contacting element 3a before the projection 2f is stopped by the shoulder of bulb base 4a, and thus the short-circuiting can not be prevented. SUMMARY OF THE INVENTION The object of the present invention is therefore to provide a terminal which solves these problems. This object is achieved with the features indicated in claim 1. Useful details are specified in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings throughout which like parts are designated by like reference numerals, and in which: Fig. 1 is a cross-sectional view schematically showing a bulb socket according to a preferred embodiment of the present invention, Fig. 2A is a side view showing a negative terminal for electrically connecting with a negative electrode of the bulb housed in the bulb socket of Fig. 1, Fig. 2B is a plan view showing the negative terminal of Fig. 2A, Fig. 2C is a bottom view showing the negative terminal of Fig. 2B, Fig. 3A is a top view showing a positive terminal for electrically connecting with a positive electrode of the bulb housed in the the bulb socket of Fig. 1, Fig. 3B is a side view showing the positive terminal of Fig. 3A, Fig. 3C is a front view showing the positive terminal of Fig. 3A, Fig. 3D is a bottom view showing the positive terminal of Fig. 3A, Fig. 4A is a cross-sectional view showing the bulb socket of Fig. 1 when the negative terminal is disengaged, Fig. 4B is a graph in assistance of explaining the relationship of gaps between the negative terminal and positive terminal in the bulb socket of Fig. 4A, Fig. 5 is a top view schematically showing a conventional bulb socket for housing a bulb having a single filament, Fig. 6 is a cross-sectional view schematically showing the bulb socket of Fig. 5, Fig. 7 is a front view showing a conventional negative terminal, Fig. 8A is a cross-sectional view schematically showing other conventional bulb socket when the negative terminal of Fig. 7 used therein is disengaged, Fig. 8B is a graph in assistance of explaining the relationship of gaps between the negative terminal and positive terminal in the bulb socket of Fig. 8A, Fig. 9 is a top view showing a conventional bulb socket for housing a double-filament bulb, Fig. 10A is a cross-sectional view showing the bulb socket of Fig. 9 when the negative terminal is disengaged, and Fig. 10B is a graph in assistance of explaining the relationship of gaps between the negative terminal and positive terminal in the bulb socket of Fig. 10A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 1, a bulb socket according to the present invention is shown. A bulb 13 indicated by an imaginary line is a double-filament bulb having two filaments (not shown) connected to a single base electrode 13e formed on an outer perimeter of a bulb base 13a. Each of the two filaments is further connected to first and second bottom electrodes 13c and 13d, respectively, formed on the bottom surface of the bulb base 13a. Specifically, the bulb socket 1 is an integral molding of an insulating resin in which a terminal insertion channel lf is formed in a surrounding wall le of a bulb insertion opening la formed at one side. The bulb socket 1 further has two positive terminal insertion holes 1g and 1h (Fig. 9) formed in a bottom wall li of the bulb insertion opening 1a. A connector insertion opening 1b is formed in the bottom wall 1i of the bulb insertion opening 1a. An insertion hole ld for inserting a connector-side connector 10n of the negative terminal 10 is formed in the center of the bottom wall 1i, and a lock channel 1c is further formed in the side wall of the insertion hole 1d. The negative terminal 10 is installed by insertion into the bulb socket 1 from the terminal insertion channel 1f. Referring to Figs. 2A, 2B, and 2C, the negative terminal 10 formed by bending a single thin strip-shaped metal piece is shown. Both long sides of a flat member 10a are folded back overlapping to a center part 10d. A bulb-side contacting element 10b is formed at one of the longer sides to be located preferably at the center of the center part when folded. Specifically, the bulb-side contacting element 10b is raised from the flat member 10a. The bulb-side contacting element 10b is bent back toward the flat member 10a at the middle so as to configure a generally V-shape. Thus, bent element 10b can resiliently swing in a direction perpendicular to the flat member 10a with respect to the base portion. The negative terminal 10 is further provided with a projection 10c formed at the side edge portion near the bottom of the bulb-side contacting element 10b. The projection 10c extends in the same direction in which the contacting element 10b is bent up. A clearance hole 10h is formed in the center 10d so as to oppose to the free end portion of the contacting element 10b such that the contacting member 10b can move into the back side of the flat member 10a when pressed. A base member 10e is provided at the bottom of the flat member 10a, and is extending in the horizontal direction perpendicular to the flat member 10a. The base member 10e has a channel-shaped recess 10f, generally in a U-shaped configuration in which a top center portion of base member 10e is removed and shoulder parts 10i and 10k are formed on both side portions thereof. The shoulder parts 10i and 10k are located near the flat member 10a and a connector-side connector 10n, respectively. The bottom part 10e is doubled over by a bottom part 10g for increased strength. The greater the width W defined by the two elevating walls of the U-shaped recess 10f, the better can contact with the positive terminal 11 be prevented. Because increasing width W weakens the strength of the base member 10e, shoulder parts 10i and 10k are left on both sides. The base member 10e is folded in a direction to oppose to the flat member 10a, as best shown in Fig. 2C. An engaging piece 10j is raised at the end of thus folded base member 10e remote from the flat member 10a. The connector-side connector 10n is formed doubled over and extending from thus folded base member 10e in a direction preferably parallel to and apart from the flat member 10a. As shown in Fig. 1, the negative terminal 10 is assembled in the bulb socket 1 with the flat member 10a inserted through the top opening la to the terminal insertion channel 1f. The connector-side connector 10n passes through the insertion hole 1d of the bottom wall li of the bulb insertion opening 1a, projecting into the connector insertion opening 1b, and the engaging piece 10j engages the channel 1c, and holds the negative terminal 10 at the normal position. With the negative terminal 10 in the above normal installation position, the bulb-side contacting element 10b and the projection 10c project to the socket center side. Referring to Figs. 3A, 3B, 3C, and 3D, the positive terminal 11 formed by bending a single thin strip-shaped metal piece is shown. The positive terminal 11 has a springlike bulb-side contacting element 11b formed into an approximate Z-shape, a connector-side connector 11d, and a base part 11a connecting therebetween. The base part 11a is provided at the bottom of the contacting element 11b and extends in a direction perpendicular thereto. The base part 11a has an engaging piece 11c raised therefrom for the engagement with the socket 1. The connector-side connector 11d extends toward the bottom from one end of the base part 11a. The bulb-side contacting element 11b is provided with a clearance channel 11e formed in one side of the horizontal part of the bottom-most part thereof. The positive terminal 11 is installed in the socket 1 such that the clearance channel 11e is set to be positioned directly over the shoulder part 10k of the negative terminal 10. The two positive terminals 11 are installed with the connector-side connector 11d inserted into the insertion holes 1g and 1h, respectively, formed in the bottom wall 1i of the socket 1. In this case, the engaging piece 11c engages the lock channel of the socket 1, and the bulb-side contacting element 11b projects parallel to the bottom of the bulb insertion opening 1a. The base part 10e of the previously installed negative terminal 10 is positioned at the bottom of one of the bulb-side contacting element 11b. As shown in Fig. 1, a gap G3 is formed between the bottom of recess 10f of the negative terminal 10 and the bottom-most horizontal part of the bulb-side contacting element 11b directly above the base part 10e. After installing one negative terminal 10 and two positive terminals 11 in the bulb socket 1 as above, the double-filament bulb 13 is installed. The pin 13b projecting from the base 13a of the bulb 13 is inserted to the L-shaped pin insertion channel 1m formed in the surrounding wall of the bulb insertion hole 1a, and the bulb 13 is turned and engaged in the bulb socket 1. With the bulb 13 installed, the bulb-side contacting element 10b of the negative terminal 10 contacts the base electrode (negative terminal) 13e of the bulb 13. In addition, the bulb-side contacting elements 11b of the positive terminals 11 contact two bottom electrodes (positive terminals) 13c and 13d provided on the bottom of the bulb base 13a. The projection 10c of the negative terminal 10 also projects to the position directly below the bottom surface 13s of the base 13a. The gap between the top surface of the projection 10c and the bulb base bottom surface 13s is G4, and gap G4 is set smaller than gap G3. Thus, when a bulb socket 1 with the negative terminal 10, positive terminals 11, and bulb 13 installed therein is mounted in a motor vehicle, etc., and vibration is applied, the engaging piece 10j of the negative terminal 10 disengages from the socket lock channel 1c, and the negative terminal 10 comes out. Referring to Fig. 4A, the bulb socket 1 when the negative terminal 10 disengaged from the socket lock lc is shown. The projection 10c positioned directly below the bottom of the bulb base 13a rises and the top thereof contacts the bottom shoulder 13s of the bulb base 13a after moving through gap G4. Thus, the negative terminal 10 is stopped and held in this position. In this stopped position, there is also a gap G5 between the recess 10f of negative terminal 10 and the bottom-most horizontal part 11b of the positive terminals 11. The shoulder part 10k, located near the positive terminal 11, can rise through the clearance channel 11e formed in the bottom-most part of the positive terminals 11 without the contact to the positive terminal 11. Thus, with the projection 10c of the negative terminal 10 being stopped against the bulb base bottom 13s, the negative terminal 10 and positive terminals 11 do not connect, and short-circuiting is prevented. Referring to Fig. 4B, a relationship of the gaps between the negative terminal 11 and the positive terminal 10 is shown. As described above, since the gap G3 is greater than gap G4, the recessed base part 10e of the negative terminal 10 does not contact the bottom-most part of the positive terminal 11b thanks to the clearance hole 11e, even when the projection 10c rises up to contact with the bottom 13s of the bulb base 13a. At that time, the negative terminal 10 and the positive terminal 11 are separated with the gap G4, and the short-circuiting therebetween is prevented. As will be known from the above description, because a projection projecting 10c toward the socket center and positioned directly below the bottom 13s of the bulb base 13a is integrally formed to the negative terminal 10, a channel-shaped recess 10f is provided in the top of the base member 10e positioned below the bottom of the positive terminals 11b, and the gap to the positive terminals 11b is increased, when the engaging piece 10j of the negative terminal 10 disengages from the lock channel 1c of the socket 1 due to vibrations, etc., and begins to come out, the projection 10c stops against the shoulder 13s of the bulb base bottom, and further removal is prevented. Because this stopped position is the position in which there is a gap G5 between the negative terminal 10 and the positive terminal 11, short-circuiting due to contact between the terminals can be prevented. Although the present invention has been fully described in connection with the preferred embodiments with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims: A bulb socket (1) with a double-filament bulb (13) received therein, the bulb (13) having a base electrode (13e) formed on the outer perimeter of a base (13a) thereof and two bottom electrodes (13c, 13d) formed on the bottom of said base (13a), the bulb socket (1) comprising: a first terminal (11) having a first contacting member (11b) for electric connection with one (13d) of said bottom electrodes; and a second terminal (10) comprising a second contacting member (10b) for the electric connection with said base electrode (13e), a projection (10c) extending toward the socket center below said base (13a), and a base member (10e) extending below said first terminal (11), characterized in that said base member (10e) has a cut-out (10f) in the top surface thereof so as not to contact said first terminal (11b) in the position where said projection (10c) contacts the bottom surface (13s) of said base (13a), and said first terminal (11) has a clearance channel (11e) which is positioned directly over a shoulder part (10k) of said cut-out (10f). A bulb socket as claimed in claim 1, wherein said second terminal (10) is formed by a single metal piece shaped to form a flat member (10a) provided with said second contacting member (10b), said projection (10c) and said base member (10e), the base member (10e) being bent in the horizontal direction perpendicular from the bottom end of the flat member (10a). A bulb socket as claimed in claim 2, wherein the second terminal (10) comprises a connector-side connector (10n) extending from said base member (10e) and projecting into a connector insertion opening (1b) of the socket (1).

Inventors: MATSUMOTO MASAYOSHI, OGAWA SHINJI, MATSUMOTO, MASAYOSHI, OGAWA, SHINJI, MATSUMOTO, MASAYOSHI, C/O ICHIKOH INDUSTRIES, LTD., OGAWA, SHINJI, C/O SUMITOMO WIRING SYSTEMS, LTD.
Applicants: ICHIKO INDUSTRIES LTD, SUMITOMO WIRING SYSTEMS, ICHIKOH INDUSTRIES LIMITED, SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1993
Main classification: H01R33
IPC codes: F21S8, F21V19, H01R33