DESCRIPTION TITLE OF THE INVENTION STARTER
BACKGROUND OF THE INVENTION Field of the Invention
[0001]
The invention relates to a starter including an electromagnetic switch.
Description of the Related Art [0002]
A starter for starting an engine of an automobile or the like is provided with an electromagnetic switch. This electromagnetic switch is one type of a linear solenoid, in which a plunger is provided in a coil as a stator, and is configured that, when a current flows through the coil, the plunger makes linear motion by generated magnetism and closes a contact of a circuit, and the current flows from a battery into a motor of the starter to start rotation of the motor.
In order to prevent entry of dust or water into a plunger sliding section of this electromagnetic switch, a boot (a waterproof cover) is provided at a tip of the plunger.
However, there has been such a problem that pressure difference is generated between the inside and the outside of

the waterproof cover along with an operation of the plunger, causing abnormal deformation of the waterproof cover. In order to avoid generation of this pressure difference, a ventilation hole is provided in the waterproof cover itself.
However, mere provision of the ventilation hole in the waterproof cover further leads to such a problem that, in the case where a portion provided with the ventilation hole is wet or covered with water, water enters through the ventilation hole, causing failure in the operation of the plunger. [0003]
To address this problem, it has been suggested to avoid the generation of the pressure difference, which is associated with the operation of the plunger, by opening the ventilation hole during the operation of the plunger and closing the ventilation hole during rest time, so as to prevent the entry of dust or water from the ventilation hole of the waterproof cover (Patent Document 1).
In addition, in order to prevent the entry of dust or water from the ventilation hole and to solve the problem caused by the pressure difference, it has been suggested to communicate between the inside of a frame of the electromagnetic switch and the inside of the motor without providing the ventilation hole in the waterproof cover (Patent Document 2).
[0004]

Patent Document 1: JP-A-2-301926
Patent Document 2: JP-A-5-126018
[0005]
The starter needs to have a simple structure due to a request of weight reduction as well as a request of downsizing that allows the starter to be housed in a limited space. Similar requests are also made to the electromagnetic switch that is used therein. In Patent Document 1 and Patent Document 2, pressure fluctuations, which are associated with the operation of the plunger, and the entry of water caused by water-wetting or flooding are raised as problems, and measures against those are suggested. However, in the measure of Patent Document 1, inundation occurs when the switch is operated during flooding. In the measure of Patent Document 2, the inundation occurs from a communication route when the inside of the motor is replaced with water. Thus, neither of them is adequate as the measure. In addition, in the related art including these of the technical literature, a problem caused by changes in temperature conditions of these of equipment and a measure against the problem have not been described. Here, the change in the temperature condition of the equipment means that the equipment (here, the electromagnetic switch as a target) arranged near a power source is exposed to a high-temperature atmosphere during traveling of a vehicle and thus is brought into a high-temperature condition; however,

the electromagnetic switch is rapidly cooled during wetting or flooding of the vehicle. Due to this change from the high-temperature condition to a low-temperature condition, negative pressure is generated in a space that includes the electromagnetic switch. Accordingly, such a phenomenon that water is sucked thereinto occurs. Technical contents of Patent Document 1 and Patent Document 2 cannot address a change in the pressure, which occurs by the change in the temperature condition, and thus are inherent to a problem of not being able to prevent the entry of water during wetting or flooding.
SUMMARY OF THE INVENTION
The invention has been made to solve the above problem and therefore has a purpose of providing a starter for which a waterproof property is secured even when a change in pressure, which is caused by a change in a temperature condition, occurs during flooding. [0006]
A starter according to the invention includes a motor, an overrunning clutch, an electromagnetic switch, and a front bracket that couples the motor, the overrunning clutch, and the electromagnetic switch. The electromagnetic switch has: an excitation mechanism in which a plunger is placed in an excitation coil; a contact mechanism that turns on/off energization of the motor by an operation of the plunger in

the excitation mechanism; a case that accommodates the excitation mechanism; and a waterproof cover provided at an opening of the case to surround the plunger in a liquid-tight manner. The waterproof cover is provided with a filter that has air permeability and does not have water permeability.
[0007]
In the starter according to this invention, in the case where the electromagnetic switch gets wet under a condition of being exposed to a high-temperature atmosphere, negative pressure that is generated by cooling the electromagnetic switch is alleviated by the air permeability of the filter. Because the filter has the air permeability but does not have the water permeability, ventilation can be provided until water inundates a space around the waterproof cover that is surrounded by the front bracket. After the space is completely filled with water, the filter stops entry of water. Thus, water does not inundate the inside of the electromagnetic switch.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS [0008]

Fig. 1 is a partial cross-sectional view of a starter according to a first embodiment of the invention;
Fig. 2 is a cross-sectional view of a periphery of a waterproof cover for a starter electromagnetic switch according to the first embodiment of the invention;
Fig. 3 includes a front view and a cross-sectional view of the waterproof cover of the invention; and
Fig. 4 is a cross-sectional view of a ventilation route in the starter electromagnetic switch of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0009] First Embodiment
A description will hereinafter be made on this embodiment by using Fig. 1, Fig. 2, Fig. 3, and Fig. 4.
Fig. 1 is a partial cross-sectional view of a configuration of a starter 100 according to the first embodiment of the invention. The starter 100 includes an electromagnetic switch 1, a motor 2, a front bracket 3, a shift lever 4, and an overrunning clutch 6 including a pinion gear 5.
The electromagnetic switch 1 includes a contact mechanism 10, an excitation mechanism 20, and a plunger structure 30. The electromagnetic switch 1 is fixed to the motor 2 by the front bracket 3.

[0010]
The contact mechanism 10 is configured by including: a battery terminal 11 that is connected to a battery positive terminal (not depicted); a motor terminal 12 that is connected to the motor 2 ; a movable contact 13 that opens/closes a current circuit; and a switch cap 14 that holds these terminals and contact.
The excitation mechanism 20 is configured by including an excitation coil 21, a fixed iron core 22, a plunger 23, and a case 24 that accommodates these and constitutes a magnetic circuit, and has a mechanical structure for causing linear motion of the plunger 23 and operating a rod 25 that extends from the movable contact 13 of the contact mechanism 10.
The plunger structure 30 is configured that the shift lever 4 is attached to a plunger hook 8 at a tip of the plunger 23 and the shift lever 4 is operated by the linear motion of the plunger 23.
[0011]
When the excitation coil 21 is energized by a starter switch (not depicted) of the excitation mechanism 20, the plunger 23 is attracted to the fixed iron core 22 side by a generated magnetomotive force. With movement of the plunger 23, the rod 25 is pushed, and the movable contact 13 connects the battery terminal 11, which is connected to a battery (not depicted), and the motor terminal 12, which is connected to

the motor 2. By this operation of the movable contact 13, electric power of the battery is supplied to the motor 2, and the motor 2 is rotationally driven. Simultaneously, the overrunning clutch 6 including the pinion gear 5 is actuated via the shift lever 4 that is engaged with the plunger hook 8, rotary power generated by the motor 2 is transmitted to a ring gear via the pinion gear 5, and an engine is thereby started.
[0012]
An outer periphery of the plunger 23 is covered with a waterproof cover 50, and the waterproof cover 50 is held between the case 24 of the electromagnetic switch 1 and the front bracket 3. More specifically, as depicted in Fig. 2, the waterproof cover 50 is attached to an opening of the case 24 of the electromagnetic switch 1 so as to cover the excitation mechanism 20 of the electromagnetic switch 1 except for the plunger hook 8. Thus, a space surrounded by the front bracket 3 exists in front of the waterproof cover 50.
[0013]
This waterproof cover 50 is provided with a filter 51. The filter 51 is constructed of a member with a feature of having a waterproof property and air permeability. More specifically, the filter 51 is constructed of a membrane with numerous holes that are smaller than a water molecule but larger than a water vapor molecule.

[0014]
As depicted in Fig. 3(1), the waterproof cover 50 is provided with a region for the filter 51 at a specified position (one upper position in Fig. 3(1)) in a peripheral edge thereof . This filter 51 has the waterproof property and the air permeability as described above. However, the filter 51 loses the air permeability in a state where the water molecules stay on a surface thereof. Thus, the filter 51 needs to be provided by selecting a position that is less likely to be covered with water. The waterproof cover 5 0 is in contact with a wall surface of the opening of the case 24 in the electromagnetic switch 1. A partition wall 53 in specified height is provided in an outer periphery and an inner periphery of this contact surface. In addition, in this embodiment, in addition to provision of the filter 51 to the waterproof cover 50, as depicted in Fig. 3(2) , a notch 52 for ventilation is provided in the partition wall 53 near the position at which the filter 51 of the waterproof cover 50 is provided. This notch 52 is provided to promote communication among partitioned spaces in the electromagnetic switch 1 as much as possible . As indicated by arrows in Fig. 4, a ventilation route is formed inside the electromagnetic switch 1 by a ventilation path formed by this notch 52.
[0015] Next, a description will be made on ventilation between

the contact mechanism 10 and the excitation mechanism 20 of the electromagnetic switch 1.
The contact mechanism 10 leads to a plunger chamber 31 through a clearance between the rod 25, which is connected to the movable contact 13, and the fixed iron core 22, and communicates with the filter 51 from a clearance between the plunger 23 and a bush 26 (see Fig. 2) through the notch 52 (see Fig. 3) of the waterproof cover 50. While ventilation can be provided from the clearance between the rod 25 and the fixed iron core 22, ventilation between a space provided with the movable contact 13 and a space in which the plunger 23 slides can be provided proactively by setting a ventilation groove (not depicted} in the rod 25 or by providing a ventilation groove (not depicted) or a ventilation hole (not depicted) in the fixed iron core 22, for example. Similarly, while the ventilation can be provided from the clearance between the plunger 23 and the bush 26, ventilation between the space in which the plunger 23 slides and a space in which the excitation coil 21 is accommodated can be provided proactively by providing a ventilation groove (not depicted) in the plunger 23 or by providing a ventilation hole 27 in the case 24 of the electromagnetic switch 1 where the excitation coil 21 is accommodated. By providing ventilation means in regions inside the electromagnetic switch 1 as described above, negative pressure in all of the spaces inside the

electromagnetic switch 1 can be alleviated. In the case where this negative pressure can be alleviated, water can be prevented from being sucked into the electromagnetic switch 1 during flooding.
[0016]
In this first embodiment, the filter 51 is provided in the waterproof cover 50, and the waterproof cover 50 is arranged on a side where the electromagnetic switch 1 is joined to the front bracket 3. With this configuration, the space surrounded by the front bracket 3 is filled with water during flooding. As an inundation route, a route from an opening of the front bracket 3 through a clearance of the shift lever 4 is established. Accordingly, air is present in the space surrounded by the front bracket 3 at a moment at which the electromagnetic switch 1 is cooled. Thus, the ventilation can be provided, and the negative pressure inside the electromagnetic switch 1 can be alleviated.
[0017]
On the contrary, in the case where the filter 51 is provided in the switch cap 14 or the case 24 of the electromagnetic switch 1, the filter 51 exerts its waterproof function as soon as the starter 100 is covered with water. Accordingly, the air permeability is lost, the air to be sucked instantaneously is unavailable, and thus the ventilation is not provided. In addition, due to the negative pressure that

is generated by cooling the electromagnetic switch 1, water inundates the inside of the electromagnetic switch 1. [0018]
In addition, in the first embodiment, with respect to the space provided with the movable contact 13, the position at which the filter 51 is provided and ambient air enters is set in a manner to extend the ventilation route from the outside to the space provided with the movable contact 13 . This allows gas to penetrate the filter 51. Thus, the air can also be replaced in a normal condition other than a condition in which the ambient air is proactively sucked by the negative pressure. For this reason, energization failure by freezing of the contact is concerned in the case where the space in which the movable contact 13 is accommodated is replaced with a high-temperature, high-humidity atmosphere and is rapidly cooled thereafter. Alternatively, conduction failure by corrosion of the contact is concerned in the case where corrosive gas enters the space. However, in the invention, the ventilation route between the outside and the space provided with the movable contact 13 is extended by providing the filter 51 in the waterproof cover 50. Accordingly, the atmosphere of the space provided with the movable contact 13 is less likely to be replaced with the ambient air, and thus durability against freezing of the contact, the conduction failure, and the like is improved.

[0019]
As it has been described so far, the starter 100 of the first embodiment of the invention includes the waterproof cover 50 for the electromagnetic switch 1 as depicted in Fig. 2. In addition, in the electromagnetic switch 1, in order to prevent the entry of water from the clearance between the switch cap 14 and the case 24, an O-ring is provided in a fitting section between the switch cap 14 and the case 24 for sealing. Accordingly, the inside of the electromagnetic switch 1 nearly achieves a completely hermetic structure. In addition, the waterproof cover 50, which includes the filter 51 with the waterproof property and the air permeability, is attached to an end of the electromagnetic switch 1, to which the front bracket 3 is attached (see Fig, 2 and Fig. 3) . By this waterproof cover 50 with the filter 51, the ventilation route is set to be extended, and the negative pressure inside the electromagnetic switch 1 is alleviated. Therefore, the entry of water during flooding can be prevented.
[0020]
In addition, the waterproof cover 50 is provided with the notch 52 so that the region provided with the filter 51 communicates with the other region. This notch 52 is configured to communicate between the partitioned spaces, which constitute the contact mechanism 10 and the excitation mechanism 20, in the electromagnetic switch 1 so as to alleviate

the negative pressure.
On the side, to which the front bracket 3 is attached, of the case 24 of the electromagnetic switch 1, the ventilation hole 27 (see Fig. 2) is formed and communicates with the filter 51. Accordingly, the ventilation can be provided between a section in which the excitation coil 21 is accommodated and the space surrounded by the front bracket 3 while the waterproof property is retained. In this way, the negative pressure inside the electromagnetic switch 1 is alleviated. Furthermore, because the filter 51 has the waterproof property, the entry of water into the section in which the excitation coil 21 of the electromagnetic switch 1 is accommodated can be prevented.
With the configuration that has been described so far, an effect of preventing the entry of water into the electromagnetic switch during flooding can reliably be obtained.
[0021]
Noted that arbitrary components of the embodiment can appropriately be changed or omitted within the scope of the invention. Various modifications and alterations of the invention will be apparent from those skilled in the art without departing from the scope and spirit of the invention, and it should be understood that this is not limited to the illustrative embodiments set forth herein.