Starter

Provided is a starter that can ensure stable insulation and exhibits excellent leakage resistance. The starter includes: a starting motor realized with a dc motor that has a commutator, positive brushes which are disposed around the commutator to abut on the commutator and connected to an external power supply, negative brushes, which are opposed to the positive brushes, stored in a bracket bearing one end of a rotation shaft; and a starting switch that is mounted on the starting motor and electrically connects or disconnects the external power supply to or from the positive brushes. When an engine is started, the starting motor is driven with the external power supply via the starting switch, and the starting motor is mechanically coupled to the engine. Herein, the starting motor has an insulating member disposed only on the internal surface of the bracket neighboring the positive brushes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a starter that starts an engine.

2. Description of the Related Art

Conventionally, for the above type of starter, a direct-current (dc) motor is adopted as a starting motor. There is a possibility that brush wear debris may be accumulated on the internal surface of a bracket and a leakage may occur between brush springs, which press respective positive brushes to a commutator or constrain the respective positive brushes to move toward the commutator, and the bracket. Therefore, a gap of a certain length or more has to be preserved between the brush springs and bracket. This imposes a limitation on a brush length and hinders durability. If the starting motor is continuously supplied with electricity for some reason, the commutator may be broken due to centrifugal force and a thermal effect. At this time, if the positive brushes, and the metallic brush springs and brush holders of the respective positive brushes are brought into contact with the internal surface of the bracket and short-circuited, there is a fear that a large current may flow upstream from the short-circuited point (for example, to a connector outside the starting motor) so as to bring about a terrible thermal damage.

As one of countermeasures, it has been proposed as described in, for example, JP-A-10-191589 that an insulating plate is attached to the inner circumferential surface of a frame, which is opposed to a brush unit, in order to ensure an insulation resistance for the frame of a dc motor and brushes.

However, the structure described in JP-A-10-191589 is such that a lead to be coupled to an external power supply is led out from the frame. The led part of the lead cannot be insulated. The aforesaid short-circuit fault cannot be therefore coped with. In addition, since an insulating plate is disposed on the internal surface of the frame so that it will be shaped like a letter C, the gap between the frame and brush springs decreases. The length of the brushes has to be decreased in consideration of assembling efficiency or the like. This degrades durability.

SUMMARY OF THE INVENTION

The present invention addresses the foregoing problems. An object of the present invention is to provide a starter that can ensure stable insulation and exhibits excellent leakage resistance.

A starter in accordance with the present invention includes: a starting motor that is realized with a dc motor having a commutator, positive brushes that are disposed around the commutator to abut on the commutator and are connected to an external power supply, and negative brushes, which are opposed to the positive brushes, stored in a bracket bearing one end of a rotation shaft; and a starting switch that is mounted outside the starting motor and electrically connects or disconnects the external power supply to or from the positive brushes. When an engine is started, the starting motor is driven with the external power supply via the starting switch, and the starting motor is mechanically coupled to the engine. The starting motor has an insulating member disposed only on the parts of the internal surface of the bracket neighboring the positive brushes.

According to the starter to which the present invention is applied, a starter that can ensure stable insulation and exhibits excellent leakage resistance can be readily provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a longitudinal view showing the overall structure of a starter in accordance with an embodiment 1 of the present invention.FIG. 2is a sectional view of a major part of the embodiment 1.FIG. 3is a longitudinal sectional view of the major part along an A-A cutting-plane line shown inFIG. 2.

Referring toFIG. 1, the starter includes a starting motor1that generates a torque, a decelerating planetary gear drive2that decelerates the rotation of the starting motor1and outputs the torque, an overrun clutch4disposed on an output shaft3of the decelerating planetary gear drive2, and a pinion5disposed to be able to slide on the output shaft3as an integral part of the overrun clutch. The starter includes a starting switch8that supplies electricity to the starting motor1and constrains the pinion5to move to a ring gear7of an engine as the integral part of the overrun clutch4via a shift lever6.

The starting switch8is located above the peripheries of the starting motor1and decelerating planetary gear drive2, and has the center axis thereof disposed substantially in parallel with the output shaft3.

The starting motor1includes a stator12that is fixed to a frame11and has a field coil12a, and a rotator13having a rotation shaft14thereof borne by the stator12. In a bracket15that bears the non-loaded side of the rotator13, a commutator16attached to the rotation shaft14and a brush unit17mounted with a gap preserved relative to the internal surface of the bracket15are stored.

The brush unit17includes, as shown inFIG. 2andFIG. 3, a pair of positive brushes18disposed around the commutator16with an angle of 90° between them, and a pair of negative brushes19. The brushes18and19are each held in a metallic brush holder22placed on a metallic base20with a resin plate21between them, and thrust on the commutator16by a metallic brush spring23attached to part of the brush holder22.

An insulating member24realized with, for example, a viscous insulating tape is bonded to the internal surface of the bracket15, which encloses the entire brush unit17, neighboring the respective positive brushes18.

The range in which the insulating member24is disposed, in an axial direction thereof, is equal to or larger than the axial distance of the brush holder22(A inFIG. 3), which supports the positive brush18, and has, in a width direction thereof, a distance equal to or larger than a width (B inFIG. 2) between a point, at which an extension of a line linking the center of the commutator16and the periphery of a brush holding member of the brush holder22meets the internal surface of the bracket15, and a point at which an extension of a line linking the center of the commutator and the periphery of the brush spring23meets the internal surface of the bracket15.

The insulating member24is realized with a glass cloth tape having glass fibers woven therein, and has two or more insulating tapes, that is, insulating tapes24aand24b, of which woven patterns are different from each other as shown inFIG. 4, or insulating tapes24cand24d, which have the weaving direction of the same woven pattern oriented differently from each other as shown inFIG. 5, superposed on each other and bonded to each other.

FIG. 6is a schematic circuit diagram of the starter. InFIG. 6, a key switch31is connected to a battery30that is the external power supply. By turning on or off the key switch31, a starting relay32is energized or de-energized. One terminal of the starting relay32is connected to the battery30, and the other terminal thereof is connected to the starting switch8. One terminal (terminal B) of the starting switch8is connected to the battery30, and the other terminal (terminal M) is connected to the positive brushes18of the starting motor1via the field coil12a.

In the foregoing constitution, when the key switch31is turned on, the starting relay32and starting switch8are biased, and the end surface of the pinion5abuts on the end surface of the ring gear7. When the starting motor1is driven and the pinion5is rotated at a high speed, the engine is cranked via the ring gear7.

In the foregoing actions, assuming that the starting motor1is continuously supplied with electric current for some reason, the commutator16may be broken due to centrifugal force and a thermal effect. In this case, if the positive brushes18and the metallic brush springs23and brush holders22of the positive brushes are brought into contact with the internal surface of the bracket15and short-circuited, a large current may flow upstream from the short-circuit point (for example, to a connector outside the starting motor) so as to bring about a terrible thermal damage. In the present embodiment, since the insulating member24is disposed on the internal surface of the bracket15neighboring the positive brushes18, the starter having the short-circuit fault effectively prevented and exhibiting excellent leakage resistance can be provided.

The range in which the insulating member24is disposed has, in the axial direction thereof the distance equal to or larger than the axial length (A inFIG. 3) of the brush holder22supporting the positive brush18, and has, in the width direction, thereof the circumferential distance equal to or larger than the width (B inFIG. 2) between the point, at which the extension of the line linking the center of the commutator16and the periphery of the brush holding member of the brush holder22meets the internal surface of the bracket15, and the point at which the extension of the line linking the center of the commutator16and the periphery of the brush spring23meets the internal surface of the bracket15. Therefore, once the insulating member24is disposed in the specified ranges, the short-circuit fault can be reliably prevented.

Further, since the insulating member24has two or more viscous insulating tapes superposed on and bonded to each other, the insulating member24can be readily attached to a predetermined range on the internal surface of the bracket15.

FIG. 7andFIG. 8are a sectional view of a major part of the embodiment 2 of the present invention and a longitudinal sectional view of the major part thereof. Instead of bonding an insulating tape as the insulating member24in the same manner as in the embodiment 1, an insulating resin24eis coated as an integral part of the bracket15over the parts of the internal surface of the bracket15neighboring the positive brushes18.

According to the embodiment 2, similarly to the embodiment 1, the short-circuit fault can be readily avoided, and the thermal damage on the connector outside the motor can be prevented.

FIG. 9is a sectional view of a major part of the embodiment 3 of the present invention. A concave part33that serves as a positioning part to be used to set the insulating member24is formed to the internal surface of the bracket15which neighbor the positive brushes18and on which the insulating member24is disposed in the embodiment 1. Specifically, the concave part33for receiving the insulating member24is formed in the range, that is, corresponding to a range in which the insulating member24is disposed has, in the axial direction thereof the distance equal to or larger than the axial length of the brush holder22supporting the positive brush18, and has, in the width direction, thereof the circumferential distance equal to or larger than the width between the point, at which the extension of the line linking the center of the commutator and the periphery of the brush holding member of the brush holder22meets the internal surface of the bracket15, and the point at which the extension of the line linking the center of the commutator and the periphery of the brush spring meets the internal surface of the bracket15.

According to the embodiment 3, the insulating member24can be accurately and readily disposed at the predetermined positions in the internal surface of the bracket15neighboring the positive brushes18.

FIG. 10is a longitudinal sectional view of a major part of the embodiment 4 of the present invention. In addition to the components of the embodiment 1, another insulating member34(made of, for example, a resin) is interposed between the end of the insulating member24disposed on the bracket15and a crossover12bof the field coil12ato which a pigtail18aof a positive brush is spliced.

According to the embodiment 4, similarly to the embodiment 1, a short-circuit fault can be avoided, and a thermal damage on a connector located outside the starting motor can be nullified. Further, there is the merit that stable insulation can be ensured.