Electromagnetic switch apparatus and starter

Abstract: An electromagnetic switch apparatus incorporating a pair of stationary contacts (61, 62) and a movable contact (67) at the rear end of a magnetic path core (55), wherein the stationary contacts (61, 62) are respectively composed of a contact part (61a, 62a) and a conductive part (61b, 62b) aligned in L-shape, wherein the conductive part (61b, 62b) at axial-directional side extends to the external circumference of an exciting coil (51), and wherein a terminal member (63) is connected to an end of this conductive part (61b, 62b) and extends in the radial direction. A pair of stationary contacts (61, 62) are respectively molded in a pair of insulating members (64a, 64b) or in an insulating member (64) secured to the rear end of the magnetic path core. An O-ring (74) is secured to the external circumference of the insulating member (64). A case (55) enveloping the exciting coil (51) and a cover member (72) enveloping the stationary (61, 62) and movable contacts (67) respectively sandwich the O-ring (74) in the axial direction to generate a water-proof sealing effect. The intermediate region of a hollow rod (58) which is secured to a movable core (56) and has the front end extended to a hollow region of an armature rotating shaft (7) is held inside the internal circumferential region of a stationary core (53) across minimal gap which narrowly allows the hollow rod (58) to slidably move in the axial direction therein.

Description: The invention relates to a starter for starting the operation of an engine, including a DC motor and an electromagnetic switch, coaxially coupled with the DC motor, for controlling the power supply to the DC motor, of the type as defined in the preamble of patent claim 1. Such a starter is known from FR-A-2 628 792. This conventional starter comprises a starter motor provided with a planetary gear. In the electromagnetic switch apparatus thereof, the conductive parts of the stationary contacts are arranged in a direction away from the exciting coil. The armature rotating shaft is provided coaxial with the output rotary shaft, wherein they are coupled with each other by means of a planetary gear. Around the output rotary shaft a pinion is mounted which can be displaced in the axial direction forward and backward through the co-operation of a pair of helical splines. This displacement is carried out by energizing an actuating element when the corresponding exciting coil is supplied with electric power. Fig. 1 illustrates a sectional view of main components of another conventional coaxial-type starter as disclosed, for example, in JP-A-238 445/1989. In this conventional device, a DC motor shown to the right of Fig. 1 is positioned in the front, whereas an electromagnetic switch apparatus shown to the left of Fig. 1 is positioned in the rear, respectively. The reference numeral 1 in Fig. 1 designates a DC motor incorporating the following elements: a relay iron member 2, a field pole 3 (a permanent magnet) which is secured to the relay iron member 2, a rear bracket 4, a a brush holder 5 which is secured to the rear bracket 4, and an armature 6 which consists of the following components: a hollow armature rotating shaft 7, an armataure core 8 which is secured to the hollow armature rotating shaft 7, an armature coil 9 which is secured to the armature core 8, and a commutator 10 which is secured to the hollow armature rotating shaft 7 and connected to the armature coil 9. The rear end of the hollow armature rotating shaft 7 is held by the rear bracket 4 through a bearing unit 11, whereas the front end of this shaft 7 is held by a bearing holder integrated with the front end itself through a bearing unit (not shown). A front bracket 13 is coupled with the relay iron member 2. The front bracket 13 incorporates an epicyclic reduction gear which is engaged with a pinion (a sun gear) provided on the external circumference of the front end of the hollow armature rotating shaft 7. The front bracket 13 also incorporates an overrunning clutch which is engaged with the output part of the epicyclic reduction gear. The rear end of an output rotary shaft 15 is held by the hollow armature rotating shaft 7 through a sleeve bearing unit 16. The intermediate region of the hollow armature rotating shaft 7 is engaged with the overrunning clutch by a helical spline. The hollow armature rotating shaft 7 transmits rotating force to the output rotary shaft 15 in order to rotate a pinion 17 which is coupled with the front end of the output rotary shaft 15 by a spline. The pinion 17 starts to move forward by the forward movement of the output rotary shaft 15, and then the pinion 17 is engaged with a ring gear of the engine so that the engine can start up its operation. The reference numeral 20 shown in Fig. 1 designates an electromagnetic switch apparatus which is coaxially coupled with the rear end of the DC motor 1. The electromagnetic switch apparatus 20 has the structure shown below. An exciting coil 21 is wound on a bobbin 22. A stationary core 23 is disposed in front of the exciting coil 21. A guide bush member 24 which is made from non-magnetic material and secured to the stationary core 23 is inserted in the internal circumference of the bobbin 22. A magnetic path case 25 made from magnetic material is coupled with the rear bracket 4 with surrounding the external periphery of the exciting coil 21. The magnetic path case 25 makes up a magnetic path core and secures the stationary iron core 23 thereto. A movable core 26 is held inside of the guide bush member 24 with facing to the stationary core 23 so that it can slidably move itself in the axial direction. The movable iron core 26 makes up a plunger and returns to the original position by effect of a compression spring 38. The rear end of a push rod 27 held by pressure of a coil spring 28 is placed inside of the movable core 26, whereas the front end of the push rod 27 presses the rear end of the output rotary shaft 15 through a steel ball 29. A pair of stationary contacts 30 are secured by means of an insulating member 31 made from plastic material. A pair of terminal bolts 30a and 30b externally project themselves from those stationary contacts 30. A lead wire from a DC power-supply source (a battery) is connected to the terminal bolt 30a. Another lead wire 32 is connected to the terminal bolt 30b by means of a nut 33 so that the lead wire 32 can be extended to a brush unit. A movable contact 34 is held behind the stationary contacts 30 through a pair of insulating members 35a and 35b. A coil spring 36 is disposed between the movable core 26 and the insulating member 35a, where the coil spring 36 gives a contact pressure to the movable contact 34. A cover member 37 made from magnetic material is installed to the rear end of the magnetic path case 25. Fig. 2 illustrates a sectional view of main components of a conventional coaxial-type starter denoting a further conventional art disclosed in JP-A-92 573/1989 for example. Those reference numerals 1 through 11 and 13 through 17 shown in Fig. 2 respectively designate component members identical to those which are shown in Fig. 1. The reference numeral 12 designates a bearing unit which is made available for holding the front end of the hollow armature rotating shaft 7. The reference numeral 20 designates an electromagnetic switch apparatus which is coaxially coupled with the rear end of the DC motor 1. The electromagnetic switch apparatus 20 has the structure shown below. An exciting coil 21 is wound on a bobbin 22. A stationary core 23 is provided in front of the exciting coil 21, whereas a rear core 18 is provided behind the exciting coil 21. A magnetic path case 25 made from magnetic material is coupled with the rear bracket 4 with surrounding the rear end and external circumference of the exciting coil 21. The magnetic path case 25 firmly secures the stationary core 23 and the rear core 18, where the magnetic path case 25 and the rear core 18 conjunctionally make up a magnetic path core. A guide bush member 24 which is made from non-magnetic material and secured to the stationary core 23 is inserted in the internal circumference of the bobbin 22. A movable core 26 is held inside of the guide bush member 24 and facing to the stationary core 23 so that the movable core 26 can slidably move in its axial direction. The movable core 26 makes up a plunger. A pair of stationary contacts 30 are secured to the rear bracket 4 through an insulating member 31. A terminal bolt 30a extends from one of the stationary contacts 30. A lead wire (not shown) extended from a DC power-supply source (a battery) is connected to the terminal bolt 30a. A hollow rod 19 made from non-magnetic material is secured to the movable core 26. A movable contact 34 directly facing to these stationary contacts 30 is held by the hollow rod 19 with an insulating member 35 intervened. The hollow rod 19 is brought back to the original position by a return spring 39. The movable contact 34 is given a contact pressure by a compression spring 38. The rear end of a push rod 27 is held in the hollow rod 19 so that the push rod 27 can move in its axial direction. This push rod 27 is energized by a coil spring 28 and carried forward by the forward movement of the movable core 26, and then, the push rod 27 pushes the output rotary shaft 15 forward through a steel ball 29. Then, the steel ball 29 is energized by another coil spring 40 until it arrives at the innermost region of the rear end of the output rotary shaft 15. A spring shoe 41 is secured to the inner rear end of the hollow rod 19. A cover member 37 is coupled with the magnetic path case 25. Furthermore, the magnetic path case 25, the rear bracket 4, and the relay iron member 2, are engaged with the front bracket 13 by means of a through bolt 42. Next, functional operations of the starter featuring the above structure are described below. As soon as the starting switch of the engine is activated, DC power flows through the exciting coil 21, and then, the movable core 26 is attracted to the stationary core 23. As a result, the push rod 27 moves forward in order to push the output rotary shaft 15 in the forward direction, thus causing the pinion 17 to be engaged with the ring gear of the engine. Simultaneously, the movable contact 34 comes into contact with a pair of stationary contacts 30. As a result, a circuit connected to the armature coil 9 closes so that DC power can flow through it to activate rotation of the armature 6. Next, rotation of the armature rotary shaft 7 is reduced by the epicyclic gear unit, and then, the decelerated rotating force is transmitted from the output rotary shaft 15 to the pinion 17 through the overrunning clutch before eventually activating the rotation of the engine itself. After turning the engine ON, the starting switch is turned OFF by the driver. Then, DC power supply to the exciting coil 21 is shut off, and then, the output rotary shaft 15 is brought back to the original position by the effect of the return spring (not shown), thus disengaging the pinion 17 from the ring gear of the engine. Simultaneously, the movable core 26 is also brought back to the original position before the movable contact 26 eventually leaves the pair of the stationary contacts 30. The above-cited conventional starter denoting the first conventional art provides a pair of stationary contacts 30 and the movable contact 34 at the rear end side of the magnetic path core, and as a result, a pair of terminal bolts 30a and 30b projecting in the radial direction from the external circumferential surfaces must necessarily be disposed at the rear end side of the electromagnetic switch apparatus 20. Depending on the structure of engine, presence of these terminal bolts 30a and 30b disturbs subsequent operation to install the starter to the engine, and also distribution of lead wires from the DC power supply source will present an obstacle. Furthermore, the rear end of the hollow rod 19 of the other conventional structure denoting the second conventional art is held by the guide bush member 24 of the movable core 26, and in addition, the intermediate region of the hollow rod 19 is held inside of the internal circumference of an insulating member 31 across a substantial gap. The insulating member 31 is held by the rear bracket 4. Since concentricity is variable by execution of assembly work, the substantial gap must be provided for the hollow rod 19. On the other hand, because of this substantial gap, the hollow rod 19 may incline or bend, thus coming into contact with the internal circumferential surface of the hollow armature rotating shaft 7. This in turn causes the hollow rod 19 to rotate with the shaft 7. Likewise, the movable contact 34 also starts to rotate, and as a result, the movable contact 34 cannot stably come into contact with the stationary contacts 30. Furthermore, metallic powder generated by the friction between the hollow rod 19 and the internal surface of the hollow armature rotating shaft 7 can easily enter into the contact chamber through the substantial gap between the insulating member 31 and the hollow rod 19. As a result, the abraded metallic powder easily adheres to the sliding surface of the contact chamber at the movable core 26, thus eventually obstructing the sliding movement between the surface of the contact chamber and the movable iron core 26 lowering the insulating effect against these contacts. Furthermore, grease of the bearing unit 11 may infiltrate into the contact chamber to obstruct a proper contact between the movable contact 34 and the stationary contacts 30. The object underlying the present invention is to provide a starter for starting the operation of an engine including a DC motor and an electromagnetic switch apparatus, coaxially coupled with the DC motor, for controlling the power supply to the DC motor, which can be constructed in a compact manner with a reduced axial length, provides a reliable insulated mounting of the stationary contacts and ensures a reliable coaxial arrangement of the armature rotating shaft and a hollow rod forming components of the electromagnetic switch apparatus. According to the invention, this object is solved in a satisfying manner by providing a starter of the type specified above which is characterized in that the conductive parts of the stationary contacts are disposed axially over the external periphery of the exciting coil starting from the second end thereof, wherein the extended axial end of one of the conductive parts is connected to the terminal member; and in that the starter further comprises an output rotary shaft whose one end is held inside of a hollow armature rotating shaft of the DC motor and the other end is provided with a pinion which is engageable with a ring gear of the engine by the movement thereof; wherein the electromagnetic switch apparatus further comprises: a hollow rod which is secured to the movable core and extends into a hollow region of the armature rotating shaft; and a push rod which is held in the hollow rod, and of which one end is pressed against the end of the output rotary shaft through a steel ball; wherein the intermediate region of the hollow rod being held in the first stationary core across a minimal gap narrowly allowing the hollow rod to slidably move therein. In one specific embodiment of the starter according to the invention, the axial end of the one of the conductive parts extends to an axial position near the second end of the exciting coil for connection to the terminal member. In another specific embodiment of the starter according to the invention, the axial end of the one of the conductive parts extends to an axial position substantially centrally between the first and second ends of the exciting coil for connection to the terminal member. In still another specific embodiment of the starter according to the invention, the axial end of the one of the conductive parts passes the first end of the exciting coil and extends to a position beyond the first stationary core for connection to the terminal member. According to a further development of the starter according to the invention, the second stationary core has a cylindrical portion which envelops the external periphery of the exciting coil, and the cylindrical portion is provided with a pair of notches for allowing the pair of conductive parts to pass therethrough. In a further development of the starter according to the invention, the pair of stationary contacts are respectively molded in the insulating member. In another further development of the starter according to the invention, the apparatus has a pair of insulating members, and each of the stationary contacts is molded in each of the pair of insulating members. In a specific embodiment of the starter according to the invention, the insulating member is in the form of a hollow disc, and each of the stationary contacts is molded in the insulating member. A further development of the starter according to the invention comprises the following components: a case which houses the exciting coil; a cover member which is coupled with the case and envelops the movable contact and the pair of stationary contacts; and an O-ring which is set to the junction between the case and the cover member and is secured to the external circumferential surface of the insulating member. The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical sectional view of a conventional starter; Fig. 2 is a vertical sectional view of another conventional starter; Fig. 3 is a vertical sectional view of the first embodiment of the invention; Fig. 4 is a vertical sectional view of the second embodiment of the invention; Fig. 5 is a vertical sectional view of the third embodiment of the invention; Fig. 6 is a perspective view showing the structure of the magnetic path core embodied by the invention; Fig. 7 is a perspective view showing the position relationship between the magnetic path core and the stationary contacts embodied by the invention; Fig. 8 is a perspective view showing another position relationship between the magnetic path core and the stationary contacts embodied by the invention; Fig. 9 is a vertical sectional view of the fourth embodiment of the invention; Fig. 10 is a vertical sectional view of the fifth embodiment of the invention; Fig. 11 is a perspective view of the insulating member in which the stationary contacts are molded in the fifth embodiment; and Fig. 12 is a sectional view of the assembled O-ring. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the accompanying drawings, the electromagnetic switch apparatus and the starter embodied by the invention are described below. The First Embodiment Fig. 3 is a vertical sectional view of the coaxial type starter applying the electromagnetic switch apparatus according to the first embodiment of the invention. The reference numeral 1 shown in Fig. 3 designates a DC motor, which incorporates a relay iron member 2 which secures a field pole 3 (a permanent magnet) thereto. The reference numeral 45 designates a rear bracket which secures a brush holder 46 thereto. The brush holder 46 holds a brush box in an insulated manner, and a brush 47 is inserted in the brush holder 46. The reference numeral 6 designates an armature which comprises the following; a hollow armature rotating shaft 7, an armature core 8 which is secured to the hollow armature rotating shaft 7, an armature coil 9 which is wound on the armature core 8, and a commutator 10 which is secured to the hollow armature rotating shaft 7 and connected to the armature core 8, respectively. The rear end of the hollow armature rotating shaft 7 is held by the rear bracket 45, whereas the front end thereof is held by a bearing holder integrated with the front end itself through a bearing unit 12. A front bracket 13 is coupled with the relay iron member 2. The front bracket 13 incorporates an epicyclic reduction gear unit which is engaged with a pinion 17 (a sun gear) provided on the external circumference of the front end of the hollow armature rotating shaft 7 and an overrunning clutch which is engaged with the output unit of the epicyclic reduction gear unit, respectively. The rear end of an output rotary shaft 15 is held by the hollow armature rotating shaft 7 through a sleeve bearing unit 16. The intermediate region of the hollow armature rotating shaft 7 is coupled with the overrunning clutch by a helical spline. The rotating force of the hollow armature rotating shaft 15 is transmitted to the output rotary shaft 15, and as a result, the pinion 17 engaged with the front end of the output rotary shaft 15 by a spline is rotated. The pinion 17 is carried forward by the forward movement of the output rotary shaft 15, and then, the pinion 17 is engaged with a ring gear (not shown) of the engine so that the engine can start up own rotation. The reference numeral 50 designates an electromagnetic switch apparatus which is coaxially coupled with the rear end of the DC motor 1, where the electromagnetic switch apparatus 50 has those structural features described below. An exciting coil 51 is wound on a bobbin 52, whereas a stationary core 53 is held in contact with the front end of the bobbin 52. The stationary core 53 partitions the internal regions of the DC motor 1 off from the electromagnetic switch apparatus 50. A bearing unit 73 like a sleeve bearing is secured to the internal surface of a projection 53a on the part of the internal circumference of the stationary core 53 in order to hold the rear end of the hollow armature rotating shaft 7. A guide bush member 54 made from non-magnetic material secured to the stationary core 53 is inserted in the internal circumference of the bobbin 52. A magnetic path case 55 made from magnetic material is coupled with the rear bracket 45 with surrounding the rear end and external circumference of the exciting coil 51. The stationary iron core 53 is secured to the front end of the magnetic path case 55 which makes up a magnetic path core itself. A movable core 56 is held in the guide bush member 54 and facing to the stationary iron core 53 so that the movable core 56 can slidably move in the axial direction. The movable core 56 makes up a plunger. A supporting rod 57 projecting itself backward is firmly inserted in the movable core 56. A hollow rod 58 made from magnetic material projects itself in the forward direction until reaching hollow space of the armature rotating shaft 7. The hollow rod 58 is secured to the movable core 56. The intermediate region of the hollow rod 58 is held by the internal circumferential portion 53b of the stationary core 53 across a minimal gap needed for allowing the hollow rod 58 to slidably move in the axial direction. The push rod 59 is held in the hollow rod 58 so that the push rod 59 can move in the axial direction. The push rod 59 is energized by a coil spring 60, and the front end of the push rod 59 presses the rear end of the output rotary shaft 15 through a steel ball 38. A pair of stationary contacts 61 and 62 are respectively provided for the rear end of the magnetic path case 55. These stationary contacts 61 and 62 are respectively composed of radial-directional contact parts 61a and 62a and axial-directional conductive parts 61b arid 62b aligned in L-shape, wherein the conductive parts 61b and 62b are disposed along the external periphery of the exciting coil 51. These stationary contacts 61 and 62 are respectively molded in plastic insulating members 64a and 64b which are secured to the rear end of the magnetic path case 55. A terminal bolt 63 penetrating the conductive part 61b of the stationary contact 61 projects in the radial direction, wherein the terminal bolt 63 penetrates the magnetic path case 55 through an insulating member 65. The terminal bolt 63 is fastened with a nut 66. A lead wire (not shown) extending from a DC power-supply source (a battery) is connected to the terminal bolt 63. An end of the conductive part 62b of the stationary contact 62 is held in contact with a receiving member 46a of the brush holder 46, wherein the lead wire of the brush 47 is connected to the receiving member 46a by a fastening screw 48. A rubber cap 49 is inserted in a hole of the rear bracket 45. A movable contact 67 opposite from the external surfaces of the stationary contacts 61 and 62 is held by an insulating holder 68 which is held by the supporting rod 57 allowing the movable contact 67 to move in the axial direction. An insulating plate 69 is inserted between the movable contact 67 and the movable core 56. A compression spring 70 is inserted between a stopper ring 71 coupled with the supporting rod 57 and the insulating holder 68 so that the movable contact 67 can respectively be energized. A cover member 72 made from non-magnetic material is secured to the magnetic path case 55. An O-ring 74 is inserted between the cover member 72 and the magnetic path case 55. Another O-ring 75 is inserted between the magnetic path case 55 and the rear bracket 45. The Second Embodiment Fig. 4 is a vertical sectional view of the electromagnetic switch apparatus according to the second embodiment of the invention. Those components with the reference numerals identical to those which are shown in Fig. 3 respectively designate the identical components used in the second embodiment. The upper half of the electromagnetic switch apparatus shown in Fig. 4 designates a state in which the movable core 56 has moved forward by the effect of an attractive force, whereas the lower half designates a state in which the movable core 56 has been brought back to its original position. As in the first embodiment, the electromagnetic switch apparatus 80 is coaxially coupled with the DC motor 1. The terminal bolt 63 connected to a lead wire extending from the DC power-supply source is connected to the end of the conductive part 61b making up the axial-directional side of one L-shaped stationary contact 61. The terminal bolt 63 projects in the radial direction through the insulating member 65 at the rear side of the exciting coil 51. The conductive part 62b making up the axial-directional side of the other L-shaped stationary contact 62 is connected to a conductive member 81 by means of a bolt 84 fastened through an insulating member by a nut 86. The conductive member 81 extends outside of the external circumference of the exciting coil 51 in the axial direction and penetrates the stationary core 53 through an insulating brush member 82. A lead wire of the brush 47 is connected to the conductive member 81. The front end of a cylindrical member 83b of a magnetic path core 83 is coupled with the rear end of the stationary core 53. A notch is provided for the cylindrical member 83b corresponding to the terminal bolt 63 and the conductive member 81. The cover member 72, the rear bracket 45, and the relay iron member, are respectively secured to the front bracket by a bolt 47. The Third Embodiment Fig. 5 is a vertical sectional view of the electromagnetic switch apparatus according to the third embodiment of the invention. Those components with the reference numerals identical to those which are shown in Figs. 3 and 4 respectively designate identical components used in the third embodiment. The upper half of the electromagnetic switch apparatus shown in Fig. 5 designates a state in which the movable core 56 has moved forward by the effect of an attractive force, whereas the lower half designates a state in which the movable core 56 has been brought back to its original position. According to the third embodiment, the position of the terminal bolt 63 is in front of the stationary core 53, in other words, the terminal bolt 63 is set to the rear bracket 45. As in the first embodiment, the electromagnetic switch apparatus 90 is coaxially coupled with the DC motor 1. The conductive part 61b of the lower L-shaped stationary contact 61 penetrates the stationary core 53 and then extends to the rear bracket 45. The conductive part 61b is connected to the terminal bolt 63 at a position between the brushes 47. The terminal bolt 63 penetrates the rear bracket 45 in the radial direction through the insulating member 65 and then projects externally. The conductive part 62b of the upper L-shaped stationary contact 62 penetrates the stationary core 53, wherein the conductive part 62b is connected to the lead wire of the brush 47 by the fastening screw 48. The hollow rod 58 firmly inserted in the movable core 56 supports the insulating holder 68 so that the insulating holder 68 can move in the axial direction. The compression spring 70 gives a contact pressure to the movable contact 67. A spring receiving member 92 is provided at the rear end of the hollow rod 58 in order to accommodate the coil spring 60. Fig. 6 is a perspective view of the magnetic path core 83 built in the electromagnetic switch apparatus of the third embodiment. Fig. 7 is a perspective view designating the relationship between the magnetic path core 83 and the stationary contacts 61 and 62. The magnetic path core 83 is composed of a vertically disposed disc plate 83a set to the rear end of the exciting coil 51 and a cylindrical member 83b. A plurality of projections are set to the front end of the cylindrical member 83b. These projections respectively pass through a plurality of holes of the stationary core 53, wherein these projections and holes are caulked with each other. Alternatively, these projections and holes can be coupled with each other with a bolt. A pair of notches 83c are provided on the external circumferential surface of the cylindrical member 83b. The conductive part 61b of the stationary contact 61 and the conductive part 62b of the other stationary contact 62 are respectively molded in the insulating members 64a and 64b. The conductive parts 61b and 62b are respectively installed in the notches 83c and project forward with horizontally penetrating the stationary core 53. Fig. 8 designates the relationship between the magnetic path core 83 and the stationary contacts 61 and 62 of the first and second embodiments, in which the end of the conductive part 61b of the stationary contact 61 and the end of the conductive part 62b of the stationary contact 62 are respectively set to the external circumference of the exciting coil 51, the terminal bolt 63 projecting in the radial direction. When executing the first through third embodiments thus far described, the conductive part 61b making up the axial-directional side of the L-shaped stationary contact 61 is set to the external circumference of the exciting coil 51 or the rear of the magnetic path core 83 beyond the external circumference of the exciting coil 51, and yet, the terminal bolt 63 connected to the end of this conductive part 61b projects in the radial direction. By virtue of this mechanical structure, the electromagnetic switch apparatus embodied by the invention can easily be installed to the engine. The internal circumference of the projection 53a and the internal circumferential portion 53b of the stationary iron core 53 can simultaneously be processed by mechanical means in order that both can be provided with precise concentricity. As a result, precise concentricity can constantly be held between the hollow rod 58 held in the internal circumferential portion 53b across a minimal gap and the hollow region of the armature rotating shaft 7 held by the bearing unit 73 secured to the inner surface of the projection 53a. In consequence, the front end of the hollow rod 58 remains apart from those inner components, and thus, metallic powder cited earlier can be prevented from ocurring (otherwise generated by abrasion)between the hollow rod 58 and those adjoining internal components. Furthermore, due to the provision of extremely minimal gap, grease of the bearing unit 73 can be prevented from flowing into the movable core 56, thus ensuring a satisfactory contact between the movable contact 67 and the stationary contacts 61 and 62. The Fourth Embodiment Fig. 9 is a vertical sectional view of the electromagnetic switch apparatus according to the fourth embodiment of the invention. Those components with the reference numerals identical to those which are shown in Figs. 3 through 5 respectively designate identical components used in the fourth embodiment of the invention. The lower half of the electromagnetic switch apparatus shown in Fig. 9 designates a state in which the movable core 56 has moved forward by the effect of an attractive force, whereas the upper half designates a state in which the movable core 56 has been brought back to its original position. According to the fourth embodiment, the terminal bolt 63 projects in the axial direction. As in the first embodiment, the electromagnetic switch apparatus 100 is coaxially coupled with the DC motor 1. The conductive part 61b of the lower L-shaped stationary contact 61 is built in the rear end of the magnetic path case 55 which itself makes up the magnetic path core of the electromagnetic switch apparatus 100. The conductive part 61b projects backward in the axial direction in conjunction with the terminal bolt 63 which also projects in the axial direction. A lead wire extending from the DC power-supply source is connected to the terminal bolt 63. In the event that the position of a terminal bolt 63 projecting in the radial direction of the electromagnetic switch apparatus should disturb a smooth installation of this apparatus to the engine, then, the structure according to the fourth embodiment is quite useful to avoid any assembly inconvenience. The Fifth Embodiment Fig. 10 is a vertical sectional view of the electromagnetic switch apparatus according to the fifth embodiment of the invention. Those components with the reference numerals identical to those which are shown in Fig. 3 respectively designate identical components introduced to the fifth embodiment. According to the first through fourth embodiments thus far described, the stationary contacts 61 and 62 are molded respectively in the insulating members 64a and 64b. However, according to the fifth embodiment, both of these stationary contacts 61 and 62 are conjunctionally molded in one insulating member 64. Fig. 11 is a perspective view showing the periphery of these components. The insulating member 64 is of hollow disc shape, through which holes 64c allowing passage of lead wires of the exciting coil 51 and further holes 64d allowing passage of bolts are respectively provided. The insulating member 64 is secured to the rear end of the magnetic path case 55 by bolts inserted in the holes 64d. The conductive part 61b of the lower stationary contact 61 in the insulating member 64 extends in the axial direction, wherein the terminal bolt 63 is connected to the extended end of the conductive part 61b. The conductive 62b of the upper stationary contact 62 further extends in the axial direction up to the position of the brush holder 46. The lead wire of the brush 47 is connected to the farthest end of the conductive part 62b by the fastening screw 48. Taking the fifth embodiment for example, the method of applying the O-ring 74 to the cover member 72 is described below. Figs. 12(a) and 12(b) respectively illustrate the way of securing the cover member 72 to the magnetic path case 55. As shown in Fig. 12(a), the O-ring 74 is set to the external circumference of the insulating member 64 coming into contact with the rear end of the magnetic path case 55. Next, as shown in Fig. 12(b), the projecting coupling member at the front end of the cover member 72 is united with the coupling recess at the rear end of the magnetic path case 55. Due to compression applied to the O-ring 74, a water-proof effect is generated. In this way, providing the external circumference of the insulating member 64 as a guiding means, the O-ring 74 is compressed by the cover member 72 and the magnetic path case 55, and yet, the O-ring 74 can easily be assembled into the system. Next, functional operation of the electromagnetic switch apparatus in conjunction with the starter as per the first through fifth embodiments is described below. The electromagnetic switch apparatus executes identical operations in all the embodiments thus far described. First, when DC power is supplied to the exciting coil 51, the movable core 56 is attracted to the stationary core 53. As a result, the push rod 59 is pushed forward by the coil spring 60. This causes the output rotary shaft 15 to move forward before engaging the pinion 17 (shown in Fig. 3) with the ring gear of the engine. At the same time, the movable contact 67 comes into contact with those stationary contacts 61 and 62 to cause DC power to flow through the armature coil 9 so that the armature 6 can be rotated. Then, the armature rotating shaft 7 rotates causing the pinion 17 also to rotate, thus starting the rotation of the engine. When the DC power supply to the exciting coil 51 is cut off, the output rotary shaft 15 is brought back to its original position by the energized force of the return spring (not shown), and as a result, the movable core 56 is also brought back to its original position. The above description has solely referred to those embodiments for applying the electromagnetic switch apparatus to a coaxial type starter. Nevertheless, the electromagnetic switch apparatus embodied by the invention is not only applicable to the coaxial type starter, but it is also effectively applicable to such a case in which the electromagnetic switch apparatus is disposed in parallel with a motor. In this case, terminal bolts externally project from conductive parts of respective stationary contacts.

Claims: A starter for starting the operation of an engine, including: a DC motor (1) and an electromagnetic switch apparatus, coaxially coupled with the DC motor (1), for controlling the power supply to the DC motor (1), the electromagnetic switch apparatus comprising an exciting coil (51) wound on a bobbin (52); a first stationary core (53) which covers a first end of the exciting coil (51); a second stationary core (83) which covers the second end of the exciting coil (51) and envelops the external periphery of the exciting coil (51), the second stationary core (83) being coupled with the first stationary core (53); a pair of stationary contacts (61, 62), respectively secured to the second stationary core (83) with an insulating member (64; 64a, 64b) therebetween; a movable core (56) held within the internal circumference of the bobbin (52) facing the first stationary core (53) and being moveable in the axial direction of the exciting coil (51) upon excitation thereof; a movable contact (67) electrically insulated from the movable core (56), which is held facing the pair of stationary contacts (61, 62) and which closes the pair of stationary contacts (61, 62) by the movement of the movable core (56); and a terminal member (63) which supplies current to the exciting coil (51) and projects radially from the axis of the exciting coil (51); wherein each of the stationary contacts (61, 62) is formed of a contact part (61a, 62a) disposed in the radial direction of the exciting coil (51) and a conductive part (61b, 62b) in the axial direction thereof; characterized in that the conductive parts (61b, 62b) of the stationary contacts (61, 62) are disposed axially over the external periphery of the exciting coil (51) starting from the second end thereof, wherein the extended axial end of one (61b) of the conductive parts (61b, 62b) is connected to the terminal member (63), in that the starter further comprises an output rotary shaft (15) whose one end is held inside of a hollow armature rotating shaft (7) of the DC motor (1) and the other end is provided with a pinion (17) which is engageable with a ring gear of the engine by the movement thereof; wherein the electromagnetic switch apparatus further comprises: a hollow rod (58) which is secured to the movable core (56) and extends into a hollow region of the armature rotating shaft (7); and a push rod (59) which is held in the hollow rod (58), and of which one end is pressed against the end of the output rotary shaft (15) through a steel ball (38); wherein the intermediate region of the hollow rod (58) being held in the first stationary core (53) across a minimal gap narrowly allowing the hollow rod (58) to slidably move therein. The starter according to claim 1, wherein the axial end of the one (61b) of the conductive parts (61b, 62b) extends to an axial position (Fig. 4) near the second end of the exciting coil (51) for connection to the terminal member (63). The starter according to claim 1, wherein the axial end of the one (61b) of the conductive parts (61b, 62b) extends to an axial position (Fig. 3) substantially centrally between the first and second ends of the exciting coil (51) for connection to the terminal member (63). The starter according to claim 1, wherein the axial end of the one (61b) of the conductive parts (61b, 62b) passes the first end of the exciting coil (51) and extends to a position (Fig. 5) beyond the first stationary core (53) for connection to the terminal member (63). The starter according to one of the claims 1 to 4, wherein the second stationary core (83) has a cylindrical portion (83b) which envelops the external periphery of the exciting coil (51), and wherein the cylindrical portion (83b) is provided with a pair of notches (83c) for allowing the pair of conductive parts (61b, 62b) to pass therethrough. The starter according to one of the claims 1 to 5, wherein the pair of stationary contacts (61, 62) are respectively molded in the insulating member (64; 64a, 64b). The starter according to one of the claims 1 to 6, wherein the apparatus has a pair of insulating members (64a, 64b), and wherein each of the stationary contacts (61, 62) is molded in each of the pair of insulating members (64a, 64b). The starter according to one of the claims 1 to 7, wherein the insulating member (64) is in the form of a hollow disc, and wherein each of the stationary contacts (61, 62) is molded in the insulating member (64). The starter according to one of the claims 1 to 8, further comprising: a case (55) which houses the exciting coil (51); a cover member (72) which is coupled with the case (55) and envelops the movable contact (56) and the pair of stationary contacts (61, 62); and an O-ring (74) which is set to the junction between the case (55) and the cover member (72) and is secured to the external circumferential surface of the insulating member (64; 64a, 64b).

Inventors: ISOZUMI SHUZOU C O HIMEJI SEIS, SHIROYAMA SHIGERU C O HIMEJI S, ISOZUMI, SHUZOU, C/O HIMEJI SEISAKUSHO, SHIROYAMA, SHIGERU, C/O HIMEJI SEISAKUSHO
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: F02N15
IPC codes: F02N15, H01H51, H01H50