Electromagnetic switch for starter

There is provided an electromagnetic switch, for a starter, that is capable of preventing a defect caused by the formation of a leakage circuit between the battery terminal and the motor terminal, even in the case where the electromagnetic switch is flooded with water. On the outer surface of a switch cap, there is provided a diaphragm disposed between the battery terminal and the motor terminal that are arranged in such a way as to be exposed outside the switch cap; the diaphragm is formed in such a way that a wall face thereof that faces one terminal, out of the battery terminal and the motor terminal, which is disposed upper than the other terminal has a protrusive shape.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic switch utilized for a starter that starts an engine, and particularly to the structure of the terminal unit thereof.

2. Description of the Related Art

In general, a starter for starting an engine is provided with a starter motor for generating torque, a speed reducer that utilizes an epicyclic gear so as to reduce the rotation speed of the rotor of the starter motor and output the torque, an overrunning clutch provided on an output axle of the epicyclic speed reducer, a pinion that is provided on the output axle along with the overrunning clutch slidably, and a shift lever that slides the overrunning clutch and the pinion along the output axle.

In addition, an electromagnetic switch for a starter is provided in the starter in an integrated manner. The electromagnetic switch for a starter includes an electromagnetic coil that is energized when the key switch of an vehicle is turned on, a plunger that is driven by electromagnetic force exerted on the electromagnetic coil when the electromagnetic coil is energized and travels so as to move the overrunning clutch and the pinion toward a ring gear of the engine, a pair of fixed contacts that are spaced apart from each other and connected with a battery and the starter motor, respectively, and a movable contact that is driven through the travel of the plunger and makes contact with the pair of fixed contacts so as to make a short circuit across the pair of fixed contacts.

The movable contact and the pair of fixed contacts are contained in a switch cap made of an insulative material. The pair of fixed contacts are connected, respectively, with a battery terminal that penetrates the switch cap from inside toward outside and a motor terminal that penetrates the switch cap from inside toward outside. On the outer surface of its axis-direction closed end, the switch cap is provided with a diaphragm disposed between the battery terminal and the motor terminal; a sufficient creepage distance between the battery terminal and the motor terminal is ensured through the diaphragm (e.g., refer to Japanese Patent Application Laid-Open No. 2004-19601).

FIG. 6is an elevation view of a terminal unit of the foregoing conventional electromagnetic switch for a starter;FIG. 7is a cross-sectional view of the terminal unit inFIG. 6in the case where the cross section taken along the line A-A is viewed along the arrow A. As illustrated inFIGS. 6 and 7, a battery terminal8and a motor terminal11are fixed in a cylindrically formed switch cap7in such a way as to penetrate the closed portion that is one end of the switch cap7in the axis direction thereof. A battery terminal strip9connected with a battery cable10and a motor terminal strip13connected with a motor lead14are connected with the battery terminal8and the motor terminal11, respectively, at the outside of the switch cap7. Additionally, a battery fixed contact8aand a motor fixed contact11aare adhered and electrically connected to one end of the battery terminal8and one end of the motor terminal11, respectively.

Between the battery terminal8and the motor terminal11, there is situated a diaphragm70that is formed on the outer surface of the closed end of the switch cap7; thus, as described above, a sufficient creepage distance between the battery terminal8and the motor terminal11is ensured. A wall face7a, of the diaphragm70, that faces the battery terminal8and a wall face7bthat faces the motor terminal11are formed in a concave shape. In some cases, the wall faces7aand7bof the diaphragm70are formed in a planar shape.

The conventional electromagnetic switch for a starter is configured in such a way that the wall face7a, of the diaphragm70of the switch cap7, that faces the battery terminal8is formed in a planar shape; therefore, in the case where the electromagnetic switch is installed in a vehicle in such a way that the battery terminal8is disposed approximately immediately above the motor terminal11, the wall face7aof the diaphragm70is likely to have a water puddle, due to a flood or the like; accordingly, under such a crucial environment as being intermittently flooded with water for a long time period, there has been a problem that the water puddle overflows into a place between the battery terminal8and the motor terminal11, whereby a leakage circuit, from the battery terminal8or the battery terminal strip9to the motor terminal11or the motor terminal strip13, is liable to be formed via the diaphragm70of the switch cap7.

Because, from the view point of production through molding a synthetic resin, there exists restriction, which depends on the wall thickness of the diaphragm, on the longitudinal (height) dimension of the diaphragm70of the switch cap7from the side end surface of the switch cap7, the diaphragm70cannot be elongated to a dimension longer that a predetermined length; in contrast, because being formed of a member the same as the member that is formed in a relatively elongated shape and forms the battery terminal8, the motor terminal11with which the motor terminal strip13is connected is formed in a relatively elongated shape, as is the case with the battery terminal8. Accordingly, as illustrated inFIG. 7, the respective front ends of the battery terminal8and the motor terminal11that are formed in a relatively elongated shape protrude over the front end of the diaphragm70of the switch cap7, whereby there exists a region where the diaphragm70is not situated between the respective front ends of the battery terminal8and the motor terminal11. As a result, there has been a problem that, under such a crucial environment as being intermittently flooded with water for a long time period, a water puddle due to the flood adheres to a place between the battery terminal8and the motor terminal11, whereby a leakage circuit, from the battery terminal8to the motor terminal11via the diaphragm70of the switch cap7, is liable to be formed.

SUMMARY OF THE INVENTION

The present invention has been implemented in order to solve the foregoing problems in the conventional electromagnetic switch for a starter; the objective thereof is to provide an electromagnetic switch, for a starter, that is capable of preventing a defect caused by the formation of a leakage circuit between the battery terminal and the motor terminal, even in the case where the electromagnetic switch is flooded with water.

An electromagnetic switch for a starter according to the present invention includes an electromagnetic coil that is energized when a key switch is turned on; a plunger that is driven by electromagnetic force produced across the energized electromagnetic coil, thereby traveling in a predetermined direction; a pair of fixed contacts that are spaced apart from each other; a movable contact that travels due to a travel of the plunger and makes contact with the pair of fixed contacts so as to make a short circuit across the pair of fixed contacts; a switch cap that is made of an insulative material and incorporates the pair of fixed contacts and the movable contact; a battery terminal that is connected with one of the pair of fixed contacts and is disposed in such a way as to be exposed outside the switch cap; and a motor terminal that is connected with the other one of the pair of fixed contacts and is disposed in such a way as to be exposed outside the switch cap. The electromagnetic switch for a starter is configured in such a way that electric power is supplied from the battery connected with the battery terminal to a starter motor connected with the motor terminal, when the movable contact makes a short circuit across the pair of fixed contacts, and is characterized in that, on the outer surface thereof, the switch cap is provided with a diaphragm disposed between the battery terminal and the motor terminal; and the diaphragm is formed in such a way that a wall face thereof that faces the battery terminal has a protrusive shape.

An electromagnetic switch for a starter according to the present invention is configured in such a way that, on the outer surface thereof, a switch cap containing a pair of fixed contacts and a movable contact is provided with a diaphragm disposed between a battery terminal and a motor terminal, and the diaphragm is formed in such a way that a wall face thereof that faces the battery terminal has a protrusive shape; therefore, even in the case where the electromagnetic switch for a starter is flooded with water, the water does not remain on the wall face of the diaphragm. Accordingly, a defect, such as an erroneous operation of the starter, caused by a leakage circuit formed between the battery terminal and the motor terminal can be prevented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An electromagnetic switch for a starter according to Embodiment 1 of the present invention will be explained below.FIG. 1is a cross-sectional view of a stator equipped with an electromagnetic switch for a starter according to Embodiment 1 of the present invention;FIG. 2is an elevation view of the terminal unit of an electromagnetic switch for a starter according to Embodiment 1 of the present invention;FIG. 3is a schematic circuit diagram of a stator utilizing an electromagnetic switch for a starter according to Embodiment 1 of the present invention.

InFIG. 1, a starter100is provided with a starter motor4for generating torque, a speed reducing unit5that is formed of an epicyclic gear mechanism that reduces the rotation speed of the rotor of the starter motor4and outputs the torque, an overrunning clutch25that is spline-combined with an output axle51of the speed reducing unit5and movably provided in the axis direction of the output axle51, and a pinion2that is provided in such a way as to slide on the output axle51along with the overrunning clutch25and to be able to engage with a ring gear1of an engine. An electromagnetic switch200for a starter, described later, is integrally fixed to a front bracket101of the starter100.

A shift lever16is mounted in such a way that it can pivot on a supporting point161, the middle point thereof; one end162of the shift lever16is engaged with the overrunning clutch25; the other end163of the shift lever16is coupled with one end of a plunger31of the electromagnetic switch200for a starter. The shift lever16and the overrunning clutch25are arranged within the front bracket101.

Next, the electromagnetic switch200for a starter will be explained. The electromagnetic switch200for a starter is situated above the outer surfaces of the starter motor4and the speed reducing unit5and is disposed in such a way that the center axis line thereof is approximately parallel to the axis line of the output axle51of the starter100. A cylindrically formed attraction coil32is fixed on the outer circumference of an insulative hollow frame33. A cylindrically formed holding coil34is disposed on the outer circumference of the attraction coil32in such a way as to be coaxial with the attraction coil32.

A core35formed of a magnetic material has a flange-shaped portion351and a cylindrical portion352; the flange-shaped portion351faces respective axis-direction ends of the attraction coil32and the holding coil34by the intermediary of the hollow frame33; the cylindrical portion352is inserted into the hollow portion of the hollow frame33. A frame36that surrounds the outer circumference of the holding coil34is formed of a magnetic material; one axis-direction end thereof is bent radially inward in such a way as to embrace the outer peripheral portion of the flange-shaped portion351of the sore35so that the core35is fixed between the hollow frame33and the frame36. The frame36and the core35configure part of a magnetic circuit for the attraction coil32and the holding coil34. The plunger31formed of a magnetic material is provided in the hollow portion of the hollow frame33in such a way as to be able to slide in the axis direction of the hollow frame33; the plunger31is attracted and moved toward the core35by the electromagnetic force produced when the attraction coil32and the holding coil34are energized.

A return spring37formed of a compression spring is disposed between the other axis-direction end of the frame36and one axial-direction end of the plunger31and always biases the plunger31along a direction in which the plunger departs from the core35. A movable contact12is fixed on the other axis-direction end of the plunger and is provided on a rod38capable of moving in the axis direction of the plunger; the movable contact12is always biased by a contact pressure spring40formed of a compression spring along a direction in which it departs from the plunger31.

One axis-direction end of a switch cap7made of an insulator such as a synthetic resin is formed as an open end, and the other axis-direction end thereof is formed as a closed end. The ring-shaped end face of the switch cap7is fixed to the frame36in such a way as to make contact with the one axis-direction end of the frame36. The movable contact12is contained in a switch cap7fixed to the frame36.

As illustrated inFIGS. 1 and 2, a battery terminal8and a motor terminal11are fixed in the switch cap7in such a way as to penetrate the closed end of the switch cap7in the axis direction of thereof. When the starter100is mounted in a vehicle, the battery terminal8is situated approximately perpendicularly above the motor terminal11. A battery fixed contact8aand a motor fixed contact11aare adhered and electrically connected to one end of the battery terminal8and one end of the motor terminal11, respectively. A battery terminal strip9connected with a battery cable10and a motor terminal strip13connected with a motor lead14are connected with the battery terminal8and the motor terminal11, respectively, at the outside of the switch cap7.

A diaphragm70that is formed on the outer surface of the closed end of the switch cap7is to ensure a sufficient creepage distance between the battery terminal8and the motor terminal11; the diaphragm70extends along the center axis of the switch cap7and is situated between the battery terminal8and the motor terminal11. A wall face7a, of the diaphragm70, that faces the battery terminal8is formed in the shape of a protrusion that has a vertex portion7a1at approximately middle of the width of the wall face7a, and whose sides gradually slant from the vertex portion7a1toward respective transverse-direction ends7a2and7a3. A wall face7b, of the diaphragm70, that faces the motor terminal11is formed in a concave shape.

Next, inFIG. 3, which is a schematic circuit diagram of the starter, the battery fixed contact8aof the electromagnetic switch200for a starter is connected with the positive-polarity terminal of a battery300mounted in a vehicle. A starter relay500is provided with a relay coil501; one end of the relay coil501is connected with the positive-polarity terminal of the battery300via a key switch400. The starter relay500includes a pair of relay fixed contacts502and503, and a relay movable contact504that is moved when the relay coil501is energized and makes contact with the pair of relay fixed contacts502and503.

The relay fixed contact502of the starter relay500is connected with the battery fixed contact8aof the electromagnetic switch200for a starter; the relay fixed contact503is connected with one terminal of the attraction coil32and one terminal of the holding coil34of the electromagnetic switch200for a starter. The motor fixed contact11aof the electromagnetic switch200for a starter is connected with the other terminal of the attraction coil32and one terminal of the armature coil of the starter motor4.

InFIGS. 1 and 3, when the key switch400is turned on, the relay coil501in the starter relay500is energized; thus, the relay movable contact504is moved to make contact with the pair of relay fixed contacts502and503; then, the pair of relay fixed contacts502and503are short-circuited. As a result, electric currents flow in the attraction coil32and the holding coil34in the electromagnetic switch200for a starter; the attraction coil32, the holding coil34, the frame36, the flange-shaped portion351and the cylindrical portion352of the core35, and the plunger31form a magnetic circuit; then, the plunger31is attracted toward the core35. Accordingly, the plunger31resists the biasing force exerted by the return spring37and travels toward the core35.

Due to the travel of the plunger31, the shift lever16pivots on the supporting point161in the counterclockwise direction with respect to the paper plane ofFIG. 1. Due to the pivot of the shift lever16, the one end162thereof makes contact with the overrunning clutch25, so that the overrunning clutch25and the pinion2are moved rightward with respect to the paper plane ofFIG. 1. As a result, the end face of the pinion2makes contact with the end face of the ring gear1, whereupon the pinion2once stops its traveling; however, on the other hand, because a relatively small current flows in the armature of the starter motor4via the relay fixed contact502, the relay movable contact504, and the relay fixed contact503of the starter relay500, and the attraction coil32of the electromagnetic switch200for a starter, the starter motor4rotates at a relatively low speed; therefore, the rotation of the starter motor4is transferred to the pinion2via the speed reducing unit5and the overrunning clutch25, so that the pinion rotates.

Because the pinion2rotates in such a way as described above, the pinion2and the ring gear1engage with each other. At the time instant when the pinion2and the ring gear1have almost completely engaged with each other, a short circuit between a pair of fixed contacts8aand11aof the electromagnetic switch200for a starter is made by the movable contact12; an large electric current flows from the battery300to the starter motor4; the high-speed rotation of the starter motor4is transferred to the pinion2via the speed reducing unit5and overrunning clutch25; then, the pinion2rotates at high speed so as to crank the engine via the ring gear1.

As described above, the wall face7aof the diaphragm70provided in the switch cap7is formed in the shape of a protrusion that has the vertex portion7a1at approximately middle of the width of the wall face7a, and whose sides gradually slant from the vertex portion7a1toward respective transverse-direction ends7a2and7a3; therefore, even in the case where the terminal portion of the electromagnetic switch200for a starter is flooded with water, the water does not remain on the wall face7aof the diaphragm70but is immediately drained away.

As described above, in the electromagnetic switch for a starter according to Embodiment 1 of the present invention, even in the case where the electromagnetic switch is flooded with water, the water does not remain on the wall face7abut is immediately drained away from the diaphragm70; thus, there can be prevented the occurrence of a defect caused by a leakage circuit formed between the battery terminal and the motor terminal.

Next, an electromagnetic switch for a starter according to Embodiment 2 of the present invention will be explained.FIG. 4is an elevation view of the terminal unit of an electromagnetic switch for a starter according to Embodiment 2 of the present invention;FIG. 5is a cross-sectional view of the terminal unit inFIG. 4in the case where the cross section taken along the line B-B is viewed along the arrow B.

InFIGS. 4 and 5, a wall face7aof a diaphragm70formed in the outer surface of the closed end of a switch cap7is formed in the shape of a protrusion that has a vertex portion7a1at approximately middle of the width of the wall face7a, and whose sides gradually slant from the vertex portion7a1toward respective transverse-direction ends7a2and7a3. A wall face7b, of the diaphragm70, that faces a motor terminal11is formed in a concave shape. A water-repellent coating75having a nature of repelling water is provided over the whole area of the wall face7aof the diaphragm70. As illustrated inFIG. 5, the motor terminal11is formed in such a way as to be shorter in the axis direction thereof than the diaphragm70that extends in the axis direction of the switch cap7.

Other configurations are the same as those in Embodiment 1 described above.

As described above, the wall face7aof the diaphragm70is formed in the shape of a protrusion that has the vertex portion7a1at approximately middle of the width of the wall face7a, and whose sides gradually slant from the vertex portion7a1toward respective transverse-direction ends7a2and7a3, and the water-repellent coating75is provided on the wall face7a; therefore, even in the case where the terminal portion of the electromagnetic switch200for a starter is flooded with water, the water does not remain on the wall face7aof the diaphragm70but is immediately drained away.

As described above, in the electromagnetic switch for a starter according to Embodiment 2 of the present invention, due to the water-repellent effect of the water-repellent coating75and the protrusive shape of the wall face7aof the diaphragm70, flood water is further rapidly drained away from the diaphragm70; thus, the occurrence of a defect caused by a leakage circuit formed between the battery terminal and the motor terminal can be prevented.

Moreover, in the electromagnetic switch for a starter according to Embodiment 2 of the present invention, the motor terminal11is formed in such a way as to be shorter in the axis direction thereof than the diaphragm70that extends in the axis direction of the switch cap7; therefore, in the case where the terminal portion of the electromagnetic switch200for a starter is flooded with water, the water that starts to flow from the axis-direction front end of the diaphragm70does not adhere to the motor terminal11, whereby a defect caused by a leakage circuit formed between the battery terminal8and the motor terminal11can more securely be prevented.

In addition, in the case of Embodiment 2 described above, the wall face7aof the diaphragm70is formed in such a way as to be protrusive, as is the case with Embodiment 1, and the water-repellent coating75is provided on the wall face7a; in addition to that, the motor terminal11is formed in such a way as to be shorter in the axis direction thereof than the diaphragm70that extends in the axis direction of the switch cap7. However, the electromagnetic switch for a starter may be configured in such a way that, as is the case with Embodiment 1, the wall face7aof the diaphragm70is formed in such a way as to be protrusive, but no water-repellent coating is provided on the wall face7aof the diaphragm70, and the motor terminal11is formed in such a way as to be shorter in the axis direction thereof than the diaphragm70that extends in the axis direction of the switch cap7. In this case, due to the protrusive shape of the wall face7aof the diaphragm70, flood water is further rapidly drained away from the diaphragm70, and the water that starts to flow from the axis-direction front end of the diaphragm70does not adhere to the motor terminal11; therefore, a defect caused by a leakage circuit formed between the battery terminal8and the motor terminal11can securely be prevented.