Coaxial engine starter

Abstract: A coaxial engine starter comprises an electric motor having an armature winding (1) of a single turn and a hollow armature rotary shaft (3) for generating a rotational force for starting an engine. The starter also comprises an over-running clutch mechanism (17) disposed within the hollow armature rotary shaft for preventing the occurrence of an excessive-speed of the armature (1) and having a pinion (20) having a gear teeth number equal to or less than seven for engaging with a ring gear of an engine upon starting of the electric motor. A solenoid switch (24) is also disposed behind the electric motor for moving a pinion shaft (20,26) forward and supplying an electric power to the electric motor.

Description: BACKGROUND OF THE INVENTION This invention relates to a coaxial engine starter for use with automotive engines. Fig. 1 is a sectional view illustrating a conventional coaxial starter disclosed in Japanese Patent Laid-Open No. 63-192962, for example. In Fig. 1, the reference numeral 1 designates an armature of a d.c. electric motor, 2 an armature core, and 3 designates a hollow armature rotary shaft having formed inside thereof a wedge-shaped cam surface 3a for providing an over-running clutch function, and the armature core is press-fit onto the outer circumference of the armature rotary shaft 3. 4 designates a commutator of the face type mounted at the rear outer circumference of the rotary shaft 3, the surface against which brushes 5 contact and slide for commutation is defined by a surface perpendicular to the rotary shaft 3. The commutator 4 is connected to an armature coil 6 wound on the core 2. The brush 5 is urged forward by a spring 5a disposed at its rear side so that the tip of the brush 5 is brought into contact under pressure onto the sliding surface of the commutator 4. 7 indicates permanent magnets mounted at the inner circumference of the yoke 8 defining a magnetic circuit for generating a magnetic field in the armature 1. The rear end of the yoke 8 is fitted onto the rear bracket 9 and the front end of the yoke 8 is fitted onto the front bracket 10. 11 indicates a bearing fitted onto the rear end of the rotary shaft 3 and is supported by the rear bracket 9. The rear bracket 9 has formed in the outer circumferential flange portion of the recess for accomodating the bearing 11 thereof a plurality of openings corresponding in position and in number to the brushes 5. 12 designates a plastic brush holder which houses therein the brush 5 and the spring 5a and has stationary contacts 13 for connection to an unillustrated terminal insert-molded at its rear portion, the stationary contacts 13 having secured thereto, by a screw 15, a terminal 14 on which a lead wire 5b of the positive side brush 5 is welded. 16 designates rollers disposed on the cam 3a formed in the inner surface of the rotary shaft 3, providing an over-running function together with roller springs. 17 designates a clutch inner member of the over-running clutch mechanism having a bearing 18 mounted on the outer circumference of the middle portion thereof to support the front end of the rotary shaft 3. 19 indicates a bearing mounted within the front bracket 10 and supports the front end of the clutch inner member 17. 17a indicates helical splines formed in the inner surface of the clutch inner member 17, the helical splines 17a engaging the helical splines 20c formed in the outer circumference of the middle portion of a pinion shaft 20 having a pinion 20a at its front end and a flange 20b for dust and water resistance. 21 indicates a stopper mounted on the rear portion of the pinion shaft 20, and 22 indicates a bearing for supporting the rear portion of the pinion shaft 20 mounted in the inner surface of the clutch inner member 17, the bearing 22 supporting the front end of a return spring 23 of the pinion shaft 20. The pinion shaft 20 is moved forward along the axis while compressing the spring 23 by the stopper 21 until the stopper 21 abut against the rear end face 17b of the clutch inner member 17 at which the forward movement is completed. 24 indicates a solenoid switch attached to the rear bracket 9 by bolts 25, the solenoid switch has a function of forwardly moving the pinion shaft 20 and a switching function for turning on the contacts to allow the power supply from the battery to the electric motor upon the closure of the key switch. 26 indicates a movable assembly for pushing the pinion shaft 20 from the behind and having a movable contact 28 supported by insulators 27a and 27b. 26a indicates a plunger, 26b a rod, 26c a second holder, 26d a first holder secured between the plunger 26a and the rod 26b and having mounted thereon the movable contact 28 and the like. The rod 26b is secured to the plunger 26a by caulking its rear end on the rear surface of the plunger 26a. 29 indicates a spring for urging the pinioin shaft 20, the spring 29 being disposed at the outer circumference of the rod 26b between the first holder 26d and the second holder 26c. 30 indicates a third holder which urges the pinion shaft 20 by a compression spring 31. 32 indicates a steel ball disposed between the front end of the third holder 30 and a recessed portion of the rear end of the pinion shaft 20 and having a function of supporting a thrust force. 33 indicates an excitation coil wound on the bobbin 33a of a plastic material for energizing the plunger 26a. 34a is a rear core and 34b is a front core, constituting together with a case 35 a magnetic circuit. 36 indicates a plate of a nonmagnetic material, which is a rear wall of the solenoid switch 24 serving as a stopper for the plunger 26a when it is rearwardly returned. 37 indicates a packing disposed between the case 35 and the plate 36 and having a water resisting function. 38 indicates a spring disposed between the plunger 26a and the front core 34b for returning the movable assembly 26 to its home position when the key switch is turned off. 39 is a through bolt connecting the rear bracket 9 and the front bracket 10. The operation will now be described. First, in the state in which key switch is off, the excitation coil 33 is not excited because it is in the non-conductive state, and since only the spring force of the spring 38 acts on the plunger 26a, the movable assembly 26 is positioned at the rear portion and the plunger 26a is brought into abutment with the plate 36. In this state, the stationary contact 13 and the movable contact 28 are in the separated state, so that the electric motor is stopped and the pinion shaft 20 is also located at the rear portion by the spring 23 and stand still with the rear surface of the flange 20b brought into abutment with the front surface of the clutch inner member 17. When key switch is turned on, the excitation coil 33 is energized to actuate the plunger 26a, causing the movable assembly 26 to move forward and the movable contact 28 to be brought into contact with the stationary contact 13. Therefore, the armature coil 6 is energized through the brush 5 and the commutator 4 thereby to start the electric motor. On the other hand, the pinion shaft 20 is pushed forward by the springs 29, 31 of the movable assembly 26, whereby the pinion 20a is brought into engagement with the ring gear formed around a fly wheel of an engine at the same time the d.c. motor is started. Immediately after the starting of the engine, the pinion shaft 20 and the clutch inner member 17 are moved together with the ring gear due to the uni-directional over-running function, idling relative to the armature 1. When the key switch is turned off when the starting has been completed, the electrical power is disconnected, the movable assembly 26 rearwardly returns due to the function of the spring 38 within the solenoid switch 24, and the pinion shaft 20 rearwardly returns by the function of the spring 23. Since the conventional coaxial starter is constructed as above described, the number of teeth of the pinion is eight at the smallest, and with such the starter, the armature winding 6 has generally two turns in order to obtain requisite torque as the d.c. motor, making unable to make the outer diameter of the rotary shaft 3 large, so that the assembly of the over-running clutch within the rotary shaft 3 is difficult and disadvantageous in performance because it is necessary to use small-diameter long rollers or a plurality of small-diameter rollers axially arranged in series. SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a coaxial engine starter free from the above-discussed problems. Another object of the present invention is to provide a coaxial engine starter in which the requisite d.c. motor torque is ensured. Another object of the present invention is to provide a coaxial engine starter in which the over-running clutch can be easily assembled and which has a superior performance. With the pinion according to the present invention, the number of the teeth of the pinion is made equal to or less than seven, thereby making the gear ratio between the engine ring gear and the pinion greater than that of pinion having the teeth number of eight which is the smallest number in the conventional design, a sufficient torque can be obtained even with a single turn armature winding, and by making the armature winding single-turn, the outer diameter of the rotary shaft can be made large, improving the easiness of assembly of the over-running clutch within the rotary shaft. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more readily apparent from the following detailed description of the preferred embodiment of the present invention taken in conjunction with the accompanying draings, in which Fig. 1 is a sectional view of the conventional coaxial engine starter; and Fig. 2 is a sectional view of the coaxial engine starter of one embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT In Fig. 2, the same reference numerals used in Fig. 1 designate the same components. 1 designates an armature of a d.c. electric motor, 2 an armature core, and 3 designates a hollow armature rotary shaft having formed inside thereof a wedge-shaped cam surface 3a for providing a function of an over-running clutch 7, and the armature core 2 is press-fit onto the outer circumference of the armature rotary shaft 3. 4 designates a commutator of the face type mounted at the rear outer circumference of the rotary shaft 3, the surface against which brushes 5 contact and slide for commutation is defined by a surface perpendicular to the rotary shaft 3. The commutator 4 is connected to an armature coil 6a wound on the core 2. According to the present invention, the armature coil 6a is a single turn coil. The brush 5 is urged forward by a spring 5a disposed at its rear side so that the tip of the brush 5 is brought into contact under pressure onto the sliding surface of the commutator 4. 7 indicates permanent magnets mounted at the inner circumference of the yoke 8 defining a magnetic circuit for generating a magnetic field in the armature 1. The rear end of the yoke 8 is fitted onto the rear bracket 9 and the front end of the yoke 8 is fitted onto the front bracket 10. 11 indicates a bearing fitted onto the rear end of the rotary shaft 3 and is supported by the rear bracket 9. The rear bracket 9 has formed in the outer circumferential flange portion of the recess for accomodating the bearing 11 thereof a plurality of openings corresponding in position and in number to the brushes 5. 12 designates a plastic brush holder which houses therein the brush 5 and the spring 5a and has stationary contacts 13 for connection to an unillustrated terminal insert-molded at its rear portion, the stationary contacts 13 having secured thereto, by a screw 15, a terminal 14 on which a lead wire 5b of the positive side brush 5 is welded. 16 designates rollers disposed on the cam 3a formed in the inner surface of the rotary shaft 3, providing an over-running function together with roller springs. 17 designates a clutch inner member of the over-running clutch mechanism having a bearing 18 mounted on the outer circumference of the middle portion thereof to support the front end of the rotary shaft 3. 19 indicates a bearing mounted within the front bracket 10 and supports the front end of the clutch inner member 17. 17a indicates helical splines formed in the inner surface of the clutch inner member 17, the helical splines 17a engaging the helical splines 20c formed in the outer circumference of the middle portion of a pinion shaft 20 having a pinion 20d at its front end and a flange 20b for dust and water resistance. According to the present invention, the number of gear teeth of the pinion 20d is equal to or less than seven. 21 indicates a stopper mounted on the rear portion of the pinion shaft 20, and 22 indicates a bearing for supporting the rear portion of the pinion shaft 20 mounted in the inner surface of the clutch inner member 17, the bearing 22 supporting the front end of a return spring 23 of the pinion shaft 20. The pinion shaft 20 is moved forward along the axis while compressing the spring 23 by the stopper 21 until the stopper 21 abut against the rear end face 17b of the clutch inner member 17 at which the forward movement is completed. 24 indicates a solenoid switch attached to the rear bracket 9 by bolts 25, the solenoid switch has a function of forwardly moving the pinion shaft 20 and a switching function for turning on the contacts to allow the power supply from the battery to the electric motor upon the closure of the key switch. 26 indicates a movable assembly for pushing the pinion shaft 20 from the behind and having a movable contact 28 supported by insulators 27a and 27b. 26a indicates a plunger, 26b a rod, 26c a second holder, 26d a first holder secured between the plunger 26a and the rod 26b and having mounted thereon the movable contact 28 and the like. The rod 26b is secured to the plunger 26a by caulking its rear end on the rear surface of the plunger 26a. 29 indicates a spring for urging the pinioin shaft 20, the spring 29 being disposed at the outer circumference of the rod 26b between the first holder 26d and the second holder 26c. 30 indicates a third holder which urges the pinion shaft 20 by a compression spring 31. 32 indicates a steel ball disposed between the front end of the third holder 30 and a recessed portion of the rear end of the pinion shaft 20 and having a function of supporting a thrust force. 33 indicates an excitation coil wound on the bobbin 33a of a plastic material for energizing the plunger 26a. 34a is a rear core and 34b is a front core, constituting together with a case 35 a magnetic circuit. 36 indicates a plate of a nonmagnetic material, which is a rear wall of the solenoid switch 24 serving as a stopper for the plunger 26a when it is rearwardly returned. 37 indicates a packing disposed between the case 35 and the plate 36 and having a water resisting function. 38 indicates a spring disposed between the plunge 26a and the front core 34b for returning the movable assembly 26 to its home position when the key switch is turned off. 39 is a through bolt connecting the rear bracket 9 and the front bracket 10. The operation will now be described. First, in the state in which key switch is off, the excitation coil 33 is not excited because it is in the non-conductive state, and since only the spring force of the spring 38 acts on the plunger 26a, the movable assembly 26 is positioned at the rear portion and the plunger 26a is brought into abutment with the plate 36. In this state, the stationary contact 13 and the movable contact 28 are in the separated state, so that the electric motor is stopped and the pinion shaft 20 is also located at the rear portion by the spring 23 and stand still with the rear surface of the flange 20b brought into abutment with the front surface of the clutch inner member 17. When the key switch is turned on, the excitation coil 33 is energized to actuated the plunger 26a, causing the movable assembly 26 to move forward until the movable contact 28 engages the stationary contact 13. Therefore, the armature coil 6 is energized through the brush 5 and the commutator 4 thereby to start the electric motor. On the other hand, the pinion shaft 20 is pushed forward by the springs 29, 31 of the movable assembly 26, whereby the pinion 20d is brought into engagement with the ring gear formed around a fly wheel of an engine at the same time the d.c. motor is started. Immediately after the starting of the engine, the pinion shaft 20 and the clutch inner member 17 are moved together with the ring gear due to the uni-directional over-running function, idling relative to the armature 1. When the key switch is turned off when the starting has been completed, the electrical power is disconnected, the movable assembly 26 rearwardly returns due to the function of the spring 38 within the solenoid switch 24, and the pinion shaft 20 rearwardly returns by the function of the spring 23. While the face-type commutator is employed as the commutator 4 in the above embodiment, a commutator of another type may equally be used. Also, while the permanent magnet 7 is used for generating a motor magnetic field, this may be replaced with a magnetic pole with a coil wound on it. Also, although the pinion shaft 20 and the pinion 20d are made integral, the pinion 20d may be spline-engaged with the pinion shaft 20 and mounted by a stopper. Further, while the above embodiment has been described as having the pinion shaft including pinion gear teeth in the inside of the clutch inner member of the over-running clutch, the pinion gear teeth and the shaft may be separate members, and any arrangement for transmiting power between the pinion and the clutch inner member of the over-running clutch can be employed. Moreover, in the above description, although the size of the teeth of the pinion or the module is not discussed, the smaller module is preferred from the view point of overall engine arrangement because the engine ring gear needs not be made large-sized, and the present invention is effective when applied to the pinion having a module of equal to or less than 2.75. Also, the greater pressure angle of the gear is preferred because the number of teeth can be made as small as possible, the preferable pressure angle being equal to or larger than 14.5°and the more preferred pressure angle being equal to or larger than 20°.

Claims: A coaxial engine starter comprising an electric motor having armature windings (6a) provided in an armature core (2) which is mounted on a hollow armature rotary shaft (3) for generating a rotational force for starting an engine; an over-running clutch mechanism (17) disposed within said hollow armature rotary shaft for preventing the occurrence of an excessive-speed of said armature and having a pinion (20) having gear teeth for engaging with a ring gear of an engine upon starting of said electric motor; and a solenoid switch (24) disposed behind said electric motor for moving a pinion shaft (20, 26) forward and supplying electric power to said electric motor, characterised in that the number of gear teeth of the pinion (20) is equal to or less than seven; the armature windings (6a) are single turn coils thereby reducing the armature core (2) thickness; and the outer and inner diameter of the rotary shaft is resultingly relatively large, thereby to enable the clutch mechanism (17) to be relatively large. A coaxial engine starter according to claim 1, wherein the pinion has a module of 2.75 or less and a pressure angle equal to or larger than 14.5°.

Inventors: ISOZUMI SHUZOO C O HIMEJI SEIS, MORISHITA AKIRA C O HIMEJI SEI, SHIROYAMA SHIGERU C O HIMEJI S, ISOZUMI, SHUZOO, C/O HIMEJI SEISAKUSHO OF, MORISHITA, AKIRA, C/O HIMEJI SEISAKUSHO OF, SHIROYAMA, SHIGERU, C/O HIMEJI SEISAKUSHO OF
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: F02N15
IPC codes: F02N11, F02N15