COAXIAL STARTER

Abstract: A coaxial starter including: a motor (25) having a tubular armature shaft (26) to which an armature (23) and a commutator (24) are attached; an output shaft (28) arranged at the front end side of the motor (25) and having one end provided with a pinion (33) disengageably engaged with a ring gear of an engine and the other end inserted into the inside path (26a) of the tubular armature shaft (26) so as to be axially slidable, the output shaft (28) having a large-diameter portion thereof; a driving power transmission device (29) having an overrunning clutch (31) for transmitting rotation force of the armature shaft (26) through the overrunning clutch (31) to the output shaft (28); a bearing (32) provided between a front end surface of the armature shaft (26), perpendicular to the axial direction thereof and the end surface of the large-diameter portion of the output shaft (28); and an electromagnetic switching unit (34) provided on a rear end side of the motor for energizing the motor and for sliding the output shaft (18).

Description: The present invention relates to a coaxial starter comprising: a motor including a tubular armature rotary shaft to which an armature having an armature core is attached; an output rotary shaft having one end provided on one end of said motor in an axial direction thereof, to which the rotation of said motor is transmittable through a one-directional clutch device, the other end of said output rotary shaft being slidable in the axial direction thereof within said tubular armature shaft; a bearing arranged to hold a front end surface of said armature shaft away from a rear end surface of a large diameter portion of said output shaft; a pinion provided on said one end of said output rotary shaft; an electromagnetic switching device provided on the other end of said motor in said axial direction thereof, said electromagnetic switching device having a rod which extends in an inner passage formed in said armature rotary shaft for allowing a sliding force to be applied to said output rotary shaft, a movable contact being attached to said rod via an insulator; a commutator attached to said rotary armature shaft; and a pair of fixed contacts connected respectively to said commutator and to a terminal bolt, said movable contact being movable into contact with said fixed contacts to effect an electrical connection between said terminal bolt to said commutator. Such a starter is known from GB-A-994 887. Another known coaxial starter for use in the engine of a vehicle is shown in Fig. 5. The conventional starter 1 as shown in Fig. 5 is constituted mainly by a DC motor 2, an overrunning clutch 4 slidably mounted on an output shaft 3, a gear train 5 for reducing the rotation force of an armature shaft 2a of the DC motor 2 to be transmitted to a clutch outer 4a of the overrunning clutch 4 through the output shaft 3, and a shift lever 8 having one end engaged with a plunger rod of an electromagnetic switching unit 6 arranged on a side of the DC motor 2 and having the other end engaged with an annular member 7 attached to the overrunning clutch 4, for making the overrunning clutch 4 slide on the output shaft 3. However, because the conventional starter 1 has a so-called biaxial structure in which the electromagnetic switching unit 6 for turning-on the power supply to the DC motor 2 is arranged on a side of the DC motor 2, the layout of the engine is very restricted when a vehicle is planned. It is an object of the present invention to provide a coaxial starter in which the overall longitudinal length is not excessive even if the electromagnetic switching unit is arranged on the rear end of the motor. According to the invention, the coaxial starter initially defined is characterized in that: said terminal bolt and a further motor-connected terminal bolt are attached to a frame for said motor between a plurality of brush devices arranged around said commutator located at the other end of said motor in the axial direction. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a sectional view showing a coaxial starter according to one embodiment of the present invention, Fig. 2 is a sectional view showing the rear end of a DC motor used in the coaxial starter of Fig. 1 in the condition that the rear bracket has been removed; Fig. 3 is a fragmentary sectional view showing a bearing provided in the front end side of the armature shaft according to another embodiment of the present invention; Fig. 4 is a fragmentary sectional view showing the bearing according to a further embodiment of the present invention; Fig. 5 is a sectional view showing a conventional biaxial starter; and Fig. 6 is a sectional view showing the coaxial starter proposed by the inventors before the present invention was created. To avoid the aforementioned disadvantage with the conventional biaxial starter, it has been proposed by the inventors that the electromagnetic switching unit is arranged on one axial end of the DC motor to thereby simplify the form of the starter like a slender cylindrical matter, as shown in Fig. 6. The basic construction according to the proposal is as follows. An armature shaft 102 of a DC motor 100 is made hollow so that a force rod 104 of an electromagnetic switching unit 103 conventionally used for operating the shift lever is allowed to extend to the output shaft 105 through an inside path 102a of the armature shaft 102. Because the armature shaft 102 of the DC motor 100 and the 104 of the electromagnetic switching unit 103 are arranged coaxially, the starter according to the proposal is called "coaxial starter". Describing the specific arrangement of the coaxial starter more in detail, the output shaft 105 has a front end (right in Fig. 6) provided with a pinion 106 engaged with a ring gear of the engine and a rear end inserted into an inside path 102a of the armature shaft 102. The output shaft 105 is provided with an insertion shaft portion 105a which is supported by a sleeve bearing 107 fixedly fitted to an inner circumferential portion of the inside path 102a to permit the output shaft 105 to slide in the axial direction. A driving power transmission device 109 including an overrunning clutch (one-way clutch 108) serves as means for transmitting driving power from the armature shaft 102 of the DC motor 100 to the output shaft 105 slidable in the axial direction. The driving power transmission device 109 is constituted by a planetary reduction gear train 110 provided in the surroundings of the front end of the armature shaft 102 and including a sun gear 110a and planetary gears 110b, and the one-way clutch 108 having a clutch outer 108a to which a central supporting shaft 111 of the planetary gears 110b is fixed and a clutch inner 108b which is engaged with a helical spline 105c formed on the outer circumference of a large-diameter portion 105b of the output shaft 105. In the proposed coaxial starter, the rear end surface at the large-diameter portion 105b of the output shaft 105 is brought into direct contact with the front end surface of the DC motor 100 when the output shaft 105, having been slid forward by the force rod 104 of the electromagnetic switching unit 103, returns to its original position. Because the rotation force of the output shaft 105 in the coaxial starter is transmitted to the engine ring gear (not shown) through the pinion 106, the output shaft 105 is driven in the reverse direction by the engine at the time of engine start so that the output shaft 105 rotates at a high speed till the pinion 106 is disengaged from the ring gear. However, the reverse transmission is cut off by the one-way clutch 108 for the purpose of protecting the DC motor, so that the high-speed rotation of the output shaft 105 driven by the engine has no influence on the armature shaft 102. Consequently, a large rotational difference arises between the armature shaft 102 and the output shaft 105 rotating at high speed by inertia. For that reason, there is the possibility of occurrence of heavy abrasion in the aforementioned, contacting portion. Also, a movable contact 113 is arranged to touch a fixed contact 112 provided on the rear portion of the electromagnetic switching unit 103 so that electrical power is supplied to the DC motor 100, and a cover 114 is arranged to cover the fixed contact 112 and the movable contact 113. As a result, the overall longitudinal length increases greatly, which interferes with a part of the engine. The coaxial starter according to the present invention will be described in detail with respect to a preferred embodiment illustrated in the accompanying drawings. Fig. 1 shows an embodiment of the coaxial starter according to the present invention. In this embodiment, the coaxial starter 20 includes a DC motor 25 which comprises permanent magnets 22 arranged at intervals on the inner circumferential surface of a yoke 21a which forms a magnetic circuit and an outer wall, an armature 23 rotatably arranged in the central portion of the yoke 21a, and a commutator 24 of a conventional type provided on the one-end side of the armature 23. The armature 23 in the DC motor 25 is constituted by a hollow armature shaft 26 and an armature core 27 attached to the outer circumference of the shaft 26. An output shaft 28 is arranged to the axially one end side of the DC motor 25, that is, to the front side (right side in Fig. 1) thereof so that rotation force is transmitted to the output shaft 28 by a driving power transmission device 29. The driving power transmission device 29 is constituted by a planetary reduction gear train 30, an overrunning clutch 31 and a helical spline 28b formed on the output shaft 28 to be engaged with a clutch inner 31a of the overrunning clutch 31. The output shaft 28 is arranged coaxially with respect to the armature shaft 26 of the DC motor 25. One end of the output shaft 28 is inserted into an inside path 26a of the armature shaft 26 so that the output shaft 28 is axially slidably supported by a bearing (sleeve bearing) 32 disposed between the output shaft 28 and the inner circumference of the armature shaft 26. The rotation force of the armature shaft 26 is transmitted to the output shaft 28 through the planetary reduction gear train 30 and the overrunning clutch 31. The planetary reduction gear train 30 is constituted by a sun gear 30a integrally formed on the outer circumference at one end of the armature shaft 26, an internal gear 30b formed at the inner surface of the yoke 21a of the motor with respect to the center of the sun gear 30a, and a plurality of planetary gears 30b engaged with the sun gear 30a and the internal gear 30b and rotatably supported by a central supporting shaft 30c fixed to a clutch outer 31b of the overrunning clutch 31. The clutch inner 31a of the overrunning clutch 31 is engaged with the helical spline 28b formed at the outer circumference of a radially outward projecting portion 28a of the output shaft 28, so that the output shaft 28 is axially slid while the rotation force is received form the clutch inner 31a. Accordingly, a pinion 33 attached to the front end of the output shaft 28 is projected from a front bracket 21b by the sliding of the output shaft 28 so that the pinion 33 is engaged with a ring gear (not shown) of the engine to rotate it. On a rear side of a rear bracket 21c fitted/attached to the rear end of the DC motor 25, there is provided an electromagnetic switching unit 34 to make the output shaft 28 slide, and to make the electric supply from a battery to the DC motor 25 possible through the closing of a key switch (not shown) of the vehicle. The electromagnetic switching unit 34 includes an excitation coil 37 wound on a plastic bobbin supported by front and rear cores 36a and 36b which form a magnetic path together with a casing 35, a plunger 38 slidably arranged to a central opening portion of the bobbin, a tubular rod 39 having one end attached to the plunger 38 and the other end extending into the inside path 26a from the rear end of the armature shaft 26, and a movable contact 41 held on the rod 39 through an insulator 40. A force rod 42 is slidably inserted into the inside of the tubular rod 39. The force rod 42 extends forward from the front-end opening portion of the tubular rod 39 so that the front end of the force rod 42 touches, through a steel ball 43, the innermost wall of a concavity formed at the end surface of the output shaft 28. The rear end of the tubular rod 39 is closed to form a block portion 39a. A coiled spring 44 is arranged within the rod 39 so that the ends of the coiled spring 44 are fixed respectively to an end surface of the block portion 39a and an end surface of the force rod 42. As the tubular rod 39 moves, the coiled spring 44 exerts pressing force to the force rod 42, so that the coiled spring 35 exerts urging force to the output shaft 28. Because the overall longitudinal length of the spring 44 can be established to be relatively long by arranging the coiled spring 44 within the tubular rod 39, a proper load can be obtained by proper spring stress. A coiled spring 48 is arranged to return the tubular rod 39 to its original position. A coiled spring 45 is also arranged to keep the steel ball 43 in a predetermined position. As shown in Fig. 1, the bearing (such as a sleeve bearing) 32 fixedly fitted to the inner circumference in the inside path 26a of the armature shaft 26 to support the output shaft 28 slidably with respect to the armature shaft 26 is constituted by a tubular bearing portion 32a to receive a radial load of the output shaft 28, and a flange-like bearing portion 32b extending radially outward at the front end portion of the tubular bearing portion 32a and interposed between the front end surface of the armature shaft 26 and the end surface of the large-diameter portion of the output shaft to receive mainly a thrust load through the large-diameter portion 28b of the output shaft. The rear end of the tubular bearing portion 32a in the bearing 32 terminates in the front of a position where the armature shaft 26 in the motor is attached to the armature core 27. This is because of the prevention of the following problems. If the bearing is extended to the mount position of the armature core, the shaft portion is often distorted when knurling is made at the central portion of the armature shaft 26 to mount the armature core thereto. There arise problems in that the pressure-receiving area of the bearing is reduced and in that the force insertion of the bearing cannot be made sufficiently. There has been well known that four brushing units 49 are arranged at equal intervals in the surroundings of the commutator 24 in the DC motor 25 as shown in Fig. 2. Further, according to the present invention, two terminal bolts 46 and 47 are arranged between the brushing units 49. The terminal bolts 46 and 47 are fixed to resin brackets 50 and 51 by molding and are positioned by attaching the resin brackets 50 and 51 into cuts formed at the circumferential surface of the rear bracket 21c, respectively. Inner ends 46a and 47a of the terminal bolts 46 and 47 held by the resin brackets 50 and 51 respectively extend, through the end surface of the rear bracket 21c, to a space where the movable contact of the electromagnetic switching unit 34 moves, thereby forming fixed contacts which can touch the movable contact 41 when the movable contact 41 comes to a predetermined position. A pair of washers 53 to each of which a wire 52 is connected are fixed to the head of one terminal bolt 46 by a nut. The wires 52 are respectively connected to brushes 49a of a pair of brushing units 49 which are opposite to each other. Brushes 49a of another pair of brushing units 49 are grounded to the corresponding base plates. A washer 55 to which a wire 54 is connected is fixed to the head of the other terminal bolt 47 by a nut. The wire 54 is connected to the positive terminal of the battery (not shown). In the following, the operation of the starter 20 will be described briefly. When a starter switch of a vehicle is closed, the electromagnetic switching unit 34 is energized to move the plunger 38 forward to thereby move the tubular rod 39. Then, the coiled spring 44 in its inside is compressed to give pressing force to the force rod 42 so that the output shaft 28 is moved forward. Accordingly, the pinion 33 is engaged with the engine ring gear and, at the same time, the movable contact 41 on the tubular rod 29 touches the fixed contacts 46a and 47a. Thus, the DC motor 25 can be powered on. As a result, the rotation force of the armature shaft 26 in the DC motor 25 is transmitted to the output shaft 28 through the planetary reduction gear train 30 and the overrunning clutch 31 so that the engine is driven by the rotation of the pinion 33. When the engine starts, the electric supply for the electromagnetic switching unit 34 is cut off. Then, the output shaft 28 is returned to its original position by the return spring arranged at a suitable place so that the pinion 33 is disengaged from the engine ring gear. However, the rotation force may be transmitted reversely from the engine during the short time required for disengaging the pinion 33 from the ring gear after the start of the engine, so that the output shaft 28 may be rotated at a high speed. The overrunning clutch 31 prevents the high-speed rotation of the output shaft 28 due to the reverse transmission from the engine from being transmitted to the DC motor 25. However, when the output shaft 28 returns to its original position, the rear end surface of the large-diameter portion 28b is brought into contact with the end surface of the flange-like bearing portion 32b of the bearing 32 while the output shaft 28 rotates at a high speed. Thus, the rear end surface of the large-diameter portion 28b of the output shaft 28 does not touch the front end surface of the armature shaft 26 directly, because the rear end surface is brought into contact with the thrust bearing portion 32b. Accordingly, abrasion of the armature shaft 26 and the output shaft 28 can be prevented. As the output shaft 28 returns, the tubular rod 39 also returns. As a result, the movable contact 41 is disconnected from the fixed contact 46 to thereby cut off the electric supply for the DC motor 25. Although the above-mentioned embodiment has shown the case where the bearing 32 is constituted by the tubular bearing portion 32a to receive a radial load and the flange-like bearing portion 32b arranged in the front end outer circumference of the tubular bearing portion 32a to receive a thrust load, it is a matter of course that the same effect can be attained by another embodiment as shown in Fig. 3 in which a large-diameter concavity 26b relatively long in the axial direction is formed in the front end side of the armature shaft 26 so that a tubular bearing 56 longer in the axial direction than the large-diameter concavity 26b is fixedly fitted into the large-diameter concavity 26b. Because the bearing 56 has its front end touching the rear end surface of the large-diameter portion 28b of the output shaft 28 and its rear end touching the inner end surface (surface perpendicular to the axial line) 26c of the large-diameter concavity 26b, the bearing 56 can receive both radial load and thrust load. The same effect can be attained by a further embodiment as shown in Fig. 4 in which a large-diameter concavity 26b having a slight length in the axial direction is formed on the inner circumference in the front end portion of the armature shaft 26 in order to interpose an annular bearing 57 between the front end surface of the armature shaft 26 and the rear end surface of the large-diameter portion of the output shaft 28 to receive only a thrust load so that the annular bearing 57 is fixedly fitted into the large-diameter concavity 26b. However, in this case, because another bearing 58 must be provided to receive a radial load, there arises a problem in that two parts are required. Although the embodiment has shown the case where a conventional commutator is used, it is a matter of course that the same effect can be attained in the case where a face type commutator is used. The resin brackets 50 and 51 to which the terminal bolts 46 and 47 are fixed by molding may be connected to each other to form a disk-like body. As described above, according to the coaxial starter of the present invention, when a part of the output shaft arranged coaxially with respect to the armature shaft tubularly provided in the motor is inserted into the inside path of the armature shaft and supported so as to be slidable in the axial direction, the front end surface of the armature shaft and the rear end surface of the large-diameter portion of the output shaft can be prevented from directly touching each other by the bearing disposed therebetween. Accordingly, abrasion due to the contact therebetween caused by the rotational difference can be prevented. Consequently, the invention can provide a coaxial starter which is excellent in durability and reliability. Also, according to the coaxial starter of the present invention, a space among the brushing units arranged in the surroundings of the commutator in the DC motor is utilized for the arrangement of the terminal bolts with the fixed contacts as constituent parts of the electromagnetic switching unit, as a result of which the overall longitudinal length of the starter is reduced. Further, according to the coaxial starter of the present invention, a rod attached to the plunger of the electromagnetic switching unit is shaped like a tube, a force rod is inserted into the tubular rod, and a coiled spring is arranged within the tubular rod so as to exert pressing force to the force rod so that the force rod receiving the pressing force exerts urging force to the output shaft. As a result, a relatively long coiled spring can be used for pressing the force rod without the increase of the overall longitudinal length of the starter. Accordingly, a proper load can be obtained by proper spring stress so that the excellent coaxial starter can be prepared. As described in the foregoing, when the electromagnetic switching unit is energized, the plunger moves. As the plunger moves, the tubular rod moves to compress the coiled spring arranged within the inside thereof to thereby give pressing force to the force rod. As a result, the output shaft is moved in the axial direction by the pressure of the force rod, so that the pinion engages with the engine ring gear and so that the movable contact provided in the tubular rod touches the fixed contact. Thus, the motor is powered on. As a result, the rotation force of the armature shaft is transmitted to the pinion through the one-way clutch to drive the engine. After the engine starts, the power supply for the electromagnetic switching unit is cut off so that the tubular rod returns to its original position as the plunger returns. Also, the output shaft returns to its original position. At this time, the end surface of the large-diameter portion of the output shaft is brought into contact with the end surface of the armature shaft through the bearing. The electric supply for the motor is also cut off while the pinion is disengaged from the engine ring gear by the return of the output shaft.

Claims: A coaxial starter, comprising: a motor (25) including a tubular armature rotary shaft (26) to which an armature (23) having an armature core (27) is attached; an output rotary shaft (28) having one end provided on one end of said motor in an axial direction thereof, to which the rotation of said motor (25) is transmittable through a one-directional clutch device (31), the other end of said output rotary shaft (28) being slidable in the axial direction thereof within said tubular armature shaft (26); a bearing (32) arranged to hold a front end surface of said armature shaft (26) away from a rear end surface of a large diameter portion of said output shaft (28); a pinion (33) provided on said one end of said output rotary shaft (28); an electromagnetic switching device (34) provided on the other end of said motor (25) in said axial direction thereof, said electromagnetic switching device (34) having a rod (39) which extends in an inner passage formed in said armature rotary shaft (26) for allowing a sliding force to be applied to said output rotary shaft (28), a movable contact (41) being attached to said rod (39) via an insulator (40); a commutator (24) attached to said rotary armature shaft; and a pair of fixed contacts (46a,47a) connected respectively to said commutator (24) and to a terminal bolt (47), said movable contact (41) being movable into contact with said fixed contacts (46a,47a) to effect an electrical connection between said terminal bolt (47) to said commutator (24), characterized in that: said terminal bolt (47) and a further motor-connected terminal bolt (46) are attached to a frame for said motor (25) between a plurality of brush devices (49) arranged around said commutator (24) located at the other end of said motor (25) in the axial direction. A coaxial starter according to claim 1 wherein: said armature (23) is attached to said tubular armature shaft (26), said tubular armature shaft (26) being provided with an inner passage thereof and a front end surface thereof perpendicular to the axial direction thereof; said pinion (33) is disengageably engagable with a ring gear of an engine and the other end of said output shaft is insertable into said inner passage of said tubular armature shaft (26) so as to be axially slidable; and a bearing (32) is provided between said front end surface of said armature shaft (26) and a rear end surface of said large-diameter portion of said output shaft (28). A coaxial starter as claimed in claim 2, wherein said tubular armature shaft (26) is provided with a large-diameter concavity formed on an inner circumferential portion at the front end side of said armature shaft (26) and said bearing is formed by a tubular member (32) which is inserted into said large-diameter concavity and longer in the axial direction than said large-diameter concavity so as to project from the front end surface of said tubular armature shaft. A coaxial starter as claimed in claim 2, wherein said bearing comprises a first bearing portion (32a) of a tubular shape for receiving a radial load, which is interposed between the inner circumferential surface of said armature shaft (26) and the outer circumferential surface of said output shaft (28), and a second bearing portion (32b) of a flange shape for receiving a thrust load, which extends radially outward on a front end side of said first bearing portion and is interposed between said front end surface of said armature shaft (26) and said rear end surface of said large-diameter portion of said output shaft (28). A coaxial starter as claimed in claim 3, wherein the rear end of said bearing terminates in front of a position where said armature core (27) of said motor (25) is attached to said armature shaft (26). A coaxial starter as claimed in claim 4, wherein the rear end of said first bearing portion (32a) terminates in front of a position where said armature core (27) of said motor is attached to said armature shaft (26). A coaxial starter as claimed in any preceding claim, wherein said electromagnetic switching device (34) is provided with a plunger (38) which is moved in the axial direction of said armature shaft when said electromagnetic switching unit is excited, said rod having one end thereof fixed to said plunger (38) and the other end thereof extending through said inside path of said armature shaft (26) so as to be in contact with an end surface of said output shaft, and a coiled spring (44) arranged within said rod (39) to urge said force rod (42) in the axial direction. A coaxial starter as claimed in claim 7, wherein said rod (39) is made of non-magnetic stainless steel.

Inventors: ISOZUMI, SHUZOO
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1988
Main classification: F02N15
IPC codes: F02N15