Magnet switch for starter

Abstract: A magnet switch which can prevent formation of dew between a movable contact and a fixed contact under the low temperature condition. A cover (20) is made of an insulating material having a base, and the fixed contact 30 is supported in the cover (20). The fixed contact (30) is connected with the tip portion (50a) of an external power feed wire (50) covered with a coating (50b). The tip (50a) is embedded in the cover (20) together with the coating (50b), thus eliminating an external power feed terminal with a large surface area that is exposed to the atmosphere. The fixed contact (30) is not cooled even under low temperature condition, and dew condensation between the fixed contact (30) and movable contact (40) can be securely prevented.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a magnet switch for starter used to start internal combustion engines. 2. Related Art: In Japanese Utility Model Publication No. 61-27467, a magnet switch for starter is disclosed. In such a magnet switch, a terminal bolt is set on the end of a fixed contact of the magnet switch, and a terminal set on the tip portion of an external power feed wire is connected to this terminal bolt and screwed in with a nut. Furthermore, a cap is used to cover the terminal bolt, external power feed wire terminal and nut. However, in the above magnet switch for starter, although there is provided the cap which covers the terminal bolt, external power feed wire terminal and nut, if the outdoor temperature is remarkably lowered, especially the external power feed wire terminal with a large surface area set on the tip of the external power feed wire that flows a large current, the terminal bolt or the connecting terminal cools a fixed contact causing formation of dew thereon. The dew will freeze, preventing a movable contact from directly contacting the fixed contact, and thus the starter may not operate. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a magnet switch for starter that can prevent formation of dew between a fixed contact and a movable contact under low temperature condition. According to the present invention, a cover has a base mode of insulating material, and a fixed contact is set in this cover. This fixed contact is connected with the tip portion of an external power feed wire of which the periphery is covered with a coating. The tip of the external power feed wire is embedded in the cover together with the coating, thus, an external power feed terminal with a large surface area that is exposed to the atmosphere is not used. Therefore, the fixed contact is not cooled even under low temperature condition, and dew condensation of formation between the fixed contact and movable contact can be securely prevented. Furthermore, no cap is nacessitated that covers the terminal bolt, nut to fix the external power feed wire and the like, thus reducing number of the component parts. Preferably, a through hole is formed from the exterior of the cover toward the fixed contact in the cover, and the tip portion of the external power feed wire is inserted into this hole and connected with the fixed contact. Thus, connection of the external power feed wire to the fixed contact is simplified, and the assembly work can be improved. More preferably, the fixed contact is formed in a U-shape, and a stay having a loosening prevention portion is plased in the U-shaped space so that the tip portion of the external power feed wire can be held between the loosening prevention portion and fixed contact. This makes the connection of the external power feed wire to the fixed contact even easier, improves the assembly work, and also securely prevents the external power feed wire from detaching from the fixed contact. Still more preferably, a pressing member to press a stay loosening prevention portion is set at a position opposing the stay loosening prevention portion of the cover. When the external power feed wire is attached or detached, the stay loosening prevention portion is press-fit with the pressing member to release the connection of the external power feed wire and fixed contact. This makes attaching and detaching the external power feed wire from the fixed contact easier. Still more preferably, a fixing member that acts as the fixed contact is fixed on the tip portion of the external power feed wire, and the external power feed wire and fixing member are molded and formed integrally with the cover. Thus, the clearance between the external power feed wire and cover is eliminated, thereby preventing water from entering and securely preventing dew from condensing between the fixed contact and movable contact. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 is a partial cross-sectional view illustrating a first embodiment of a magnet switch for starter according to the present invention; Fig. 2 is a perspective view illustrating a fixed contact used in the embodiment of Fig.1; Fig. 3 is a perspective view illustrating a stay used in the embodiment of Fig. 1; Fig. 4 is a partial cross-sectional view illustrating a second embodiment of a magnet switch for starter according to the present invention; Fig. 5 is a partially enlarged cross-sectional view of a part taken along the V-V line in Fig. 4; and Fig. 6 is a partial cross-sectional view illustrating a third embodiment of a magnet switch for starter according to the present invention. DETAILED DESCRIPTION OH THE PREFERRED EMBODIMENTS The first embodiment of a magnet switch for starter according to the present invention will be described with reference to Figs. 1 through 3. In Fig. 1, reference numeral 10 denotes a magnet switch for starter, and numeral 20 denotes a cover having a base made of, for instance, heat-hardening phenolic resin. A pair of fixed contacts 30 and 31 positioned relatively to a disk-like movable contact 40 (described later) are plased or set inside the cover 20. As shown in Fig. 2, the fixed contact 30 is formed in a generally U-shape. Multiple grooves 30a are formed on one inside wall of the U-shape. A copper wire portion 50a of an external power feed wire 50 described later contacts these grooves 30a. The fixed contact 30 is fixed in such a way that the tip 30b of the fixed contact 30 directly contacts the inner wall of the cover 20. A stay 60 has a loosening prevention portion 60a of which the end is formed in a V-shape as shown in Fig. 3 and is placed inside the space of the fixed contact 30. The stay 60 is made of an elastic conductive plate (e.g., copper plate) and is set so that the loosening prevention portion 60a is positioned to face the grooves 30a of the fixed contact 30. The external power feed wire 50 is covered with a sheath or coating 50b, and the tip portion is formed with the copper wire portion 50a that is connected to the fixed contact 30 at the grooves 30a. The electric power is fed from a vehicle storage battery (not illustrated) to the fixed contact 30. The external power feed wire 50 is inserted into the cover 20 through a through hole 22 formed from the outside to the inside. The copper wire portion 50a is fixed between the loosening prevention portion 60a and fixed contact 30. A fixed contact 31 formed as a pair with the fixed contact 30 is fixed to a terminal bolt 31a of which the lead wire (not illustrated) that feeds the electric power to a starter motor (not illustrated) is connected. This terminal bolt 31a is also fixed to the cover 20 by a washer 90. A first spring 70 biases the movable contact 40 in the direction distanced away from the fixed contact 30, and a second spring 80 biases the movable contact 40 in the direction to the fixed contact 30. When the movable contact 40 directly contacts the fixed contact 30, the electric power is fed from the battery (not illustrated) to the starter motor (not illustrated) in the well known manner. With this structure, the tip portion of the external power feed wire 50 is embedded in the cover 20 together with the coating 50b, so there is no external power feed wire terminal with a large surface area that is exposed to the atmosphere. Therefore, the fixed contact 30 is not cooled, and dew condensation or formation between the fixed contact 30 and movable contact 40 can be securely prevented. Furthermore, the terminal bolt, nut to fix the external power feed wire and a cap to cover the contact bolt, external power feed wire terminal and nut is not required, so the number of component parts can be reduced. The through hole 22 is formed from the exterior of the cover 20 toward the fixed contact 30 within the cover 20, and the tip portion of the external power feed wire 50 is inserted in the hole 22 and connected with the fixed contact 30. Thus, connection of the external power feed wire 50 to the fixed contact 30 can be simplified, and the assembly work can be improved. The fixed contact 30 is formed into the U-shape, and the stay 60 having the loosening prevention portion 60a is set in the U-shaped space so that the tip portion of the external power feed wire 50 can be held between the loosening prevention portion 60a and fixed contact 30. This makes the connection of the external power feed wire 50 to the fixed contact 30 even easier, improves the assembly work, and also securely prevents the external power feed wire 50 from detaching from the fixed contact 30. The grooves 30a further assures electrical and mechanical connection of the wire 50 to the fixed contact 30. Other embodiments will be described with reference to Figs. 4 through 6. Fig. 4 is a partial cross-sectional view of the magnet switch for starter according to the second embodiment and Fig. 5 is a partialy enlarged cross-sectional view illustrating the a cross-section taken along the line V-V in Fig. 4. In the second embodiment illustrated in Figs. 4 and 5, a presssing member 61 is disposed to press the loosening prevention portion 60a of the stay 60, and a spring 100 is disposed to biases the pressing member 61 in the direction away from the loosening prevention member 60a, i.e., upwardly in Figs. 4 and 5. Those are set in a first groove 23 formed in the radial direction of the cover 20 which is generally cylindrical. The spring 100 is set between the pressing member 61 and the upper end 39d of the fixed contact 30. To assemble the external power feed wire 50, the copper wire portion 50a of the external power feed wire 50 is passed through the through hole 22 in the cover 20 toward the loosening prevention portion 60a of the stay 60 while slackening the loosening prevention portion 60a. The copper wire portion 50a is fixed between the fixed contact 30 and the loosening prevention portion 60a of the stay 60. To detach the external power feed wire 50, i.e. a battery cable, the pressing member 61 is pressed down toward the loosening prevention portion 60a against the spring 100 through a second groove 24 having a smaller diameter than the first groove 23. Thus, the loosening prevention portion 60a is directly contacted and deformed. This releases the direct contact of the copper wire portion 50a of the external power feed wire 50 and the loosening prevention portion 60a, and the external power feed wire 50 separates from the fixed contact 30. With this structure, the external power feed wire 50 can be freely attached or detached with ease without detaching the cover. Next, in the third embodiment illustrated in Fig. 6, an L-shaped fixing member 32 is attached to the copper wire portion 50a of the external power feed wire 50, and the external power feed wire 50 and fixing member 32 are molded and formed integrally with the cover 20. In this case, one end (leftmost part in Fig. 6) of the fixing member 32 is used as the fixed contact. The fixing member 32 is formed of a copper plate or a copper-plated metal, for example. In each of the above embodiments, the terminal bolt 31a is used for the fixed contact 31, however, the lead wire and fixed contact 31 can be connected to the starter motor to achieve the same structure as the fixed contact 30. The present invention has been described with reference to the presently preferred embodiments illustrated in the accompanying drawings. It is to be understood, however, that the present invention should not be restricted to the above-described embodiments but may be modified without departing from the scope of the invention, as defined in the claims.

Claims: A magnet switch for starter comprising: a fixed contact (30); a movable contact (40) movable to contact said fixed contact; a cover (20) made of an insulating material and having a bottom for supporting said fixed contact; and an external power feed wire (50) having a tip portion (50a) connected with said fixed contact and covered with a coating (50b) except for said tip portion; wherein said tip portion of said external power feed wire is encased within said cover with said coating. The magnet switch for starter according to claim 1, wherein said cover (20) is formed with a through hole (22) on said bottom at a position facing said fixed contact, and wherein said external power feed wire (50) passes through said hole with said coating contacting said cover. The magnet switch for starter according to claim 2, wherein said fixed contact (30) is formed in generally U-shape (Fig. 2), wherein a stay (60) having loosening prevention portion (60a) preventing at a tip thereof is disposed in a space of said U-shape, and wherein said tip portion (50a) of said external power feed wire is held between said loosening prevention portion and said fixed contact. The magnet switch for starter according to claim 3 further comprising: a pressing member (61) placed movably in said cover at a position opposing said loosening prevention portion for deforming said loosening prevention portion when pressed from outside of said cover, so that connection of said tip portion of said external power feed wire with said fixed contact is released. The magnet switch for starter according to claim 1, wherein a fixing member (32) is attached to said tip portion of said external power feed wire as said fixed contact, and wherein said external power feed wire and said fixing member are molded and formed integrally with said cover with a part of said fixing member being exposed from said cover for connection with said fixed contact (Fig. 6). A magnet switch comprising: an electric power lead wire (50) covered with a coating (50b); a fixed contact (30) connected with said lead wire; a movable contact (40) movable to contact with said fixed contact; a cap (20) made of an electrically insulated material and formed in a generally cup shape to encase said movable contact and said fixed contact therein, said cap having a hole (22) on a bottom of said cup shape for passing said lead wire therethrough with said coating of said lead wire contacting therewith in said hole. A magnet switch according to claim 6, further comprising: a stay (60) interposed between said lead wire and said fixed contact and having a loosening prevention portion (60a) formed to keep said lead wire fixed to said fixed contact; a pressing member (61) placed in said cap at a position opposing said loosening prevention portion of said stay and deforming said loosening prevention portion to release connection of said lead wire and said fixed contact, when pressed; and external means (24) formed on said cap for enabling pressing of said pressing member from outside said cap so that said connection of said lead wire and said fixed contact is released without removal of said cap. A magnet switch according to claim 7, further comprising: a spring (100) disposed in said cap and normally biasing said pressing member in a direction away from said loosening prevention portion. A magnet switch according to claim 8, wherein said external means (24) includes a hole formed on said cap through which said pressing member is pressed externally.

Inventors: HAYASHI NOBUYUKI, OHMI MASANORI, SHIGA TSUTOMU, HAYASHI, NOBUYUKI , OHMI, MASANORI, SHIGA, TSUTOMU
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1995
Main classification: H01H51
IPC codes: H01H51