ENGINE STARTER

Abstract: An engine starter (10) is provided in which a pinion (25), which is engaged or disengaged with a ring gear of the engine to be started, is formed as an integral part of a drive shaft (15) at an end of the drive shaft which is movable in the axial direction thereof while being rotated an electric motor (11). The engine starter has no restriction as to the root thickness of the pinion or the number of teeth of the pinion, and has a large gear ratio to the ring gear.

Description: The present invention relates to an engine starter which is used in starting automotive engines, particularly to an engine starter equipped with a drive shaft which rotates upon receipt of driving force of an electric motor and, moves in the axial direction thereof. There have been engine starters equipped with drive shafts which move in the axial direction thereof while rotating due to the driving force of an electric motor, an example of which being that laid open in the Patent Application Laid-Open No.63-90665. In this and other engine starters of the prior art, a pinion which is engaged or disengaged with a ring gear of the engine to be started is fitted, by means of a straight spline or the like, on the periphery of the front end of the drive shaft which moves axially while rotating. Also installed at the front end of the drive shaft which protrudes beyond the end face of the pinion is a stopper which prevents the pinion from dropping off. The engine starter laid open in the publication mentioned above is a coaxial type engine starter, and is equipped with an electromagnetic switch which switches on the power to the electric motor disposed at the rear of the electric motor. Therefore, although the entire configuration is a thin cylinder and the construction is simple, its total length is greater than that of a 2-axis type engine starter. In order to make effective use of the space in the engine room of an automobile or to reduce the weight of an automobile, automotive parts are required to become smaller in size. Engine starters, either coaxial or 2-axis type, are strongly required to become smaller, particularly in length. DE-A-3809684 discloses an engine starter which comprises an electric motor, a drive shaft and an overrun clutch mechanism. The drive shaft is rotated by the electric motor, and is movable in the axial direction. The drive shaft has a pinion, engageable with a ring gear of the engine, and a stopper, which limits the axial travel of the drive shaft by contact with the clutch inner. Accordingly, the invention provides an engine starter, comprising: an electric motor; a drive shaft which is rotated by said electric motor and is movable in its own axial direction, an end of said drive shaft being formed into a pinion, said pinion being engageable with a ring gear of an engine, said engagement being dependent on the axial position of said pinion; a stopper fixed to said drive shaft; an overrun clutch mechanism equipped with a clutch inner, a first end of said clutch inner being engaged with said drive shaft, said clutch inner having a shoulder section within the range of movement of said stopper, characterized in that at all positions of the stopper, the stopper is within the clutch inner. The driving force of the electric motor is transmitted to the drive shaft, thereupon the pinion rotates. The drive shaft is thrusted forward so that the pinion comes in mesh with the ring gear of the engine. Because the pinion is incorporated into the drive shaft, the number of teeth of the pinion is not limited by the root thickness of the pinion or the strength of the drive shaft. One object of the present invention is to provide an engine starter where the ratio of the pinion gear to the ring gear can be increased because the number of pinion gear teeth is not limited. Another object of the present invention is to provide an engine starter where the electric motor is made compact and the total length is reduced. Further another object of the present invention is to provide an engine starter where a stopper which prevents the pinion from dropping off is not needed. The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. Fig. 1 is a partial cutaway drawing illustrative of an embodiment of the engine starter of the present invention, and Fig. 2 is a partial cutaway drawing illustrative of another embodiment of the engine starter of the present invention. Fig. 1 shows the engine starter 10 of an embodiment of the present invention. The engine starter of this embodiment is of coaxial type. In this drawing, 11 is a DC electric motor which has an armature rotary shaft 12 of a cylindrical shape. Disposed at the rear of the electric motor 11 is an electromagnetic switch 13 composed of an electromagnetic solenoid. The electromagnetic switch 13 has a plunger rod 13a which passes through an internal passage 14 of the armature rotary shaft 12. At the front of the armature rotary shaft 12, a drive shaft 15 is disposed coaxially therewith. The rear end of the drive shaft 15 is inserted into the internal passage 14. The rear end face of the drive shaft 15 and the front end face of the plunger rod 13a face oppositely to each other. When the electromagnetic switch 13 is closed, the plunger rod 13a is thrusted forward so that the front end face of the plunger rod 13a comes into contact with the rear end face of the drive shaft 15, thereby thrusting the drive shaft 15 forward. Connected to the periphery of the front end of the armature rotary shaft 12 is a sun gear 16a. The sun gear 16a is in mesh with a plurality of planetary gears 16b. These planetary gears 16b mesh with an internal gear 16c which is provided on the internal surface of a frame 17. The planetary gears 16b are supported by a shaft 16d onto a carrier 16e. A planetary gear mechanism 16 which consists of the sun gear 16a, the planetary gears 16b, the internal gear 16c, the shaft 16d and the carrier 16e as described above reduces the revolution speed of the armature rotary shaft 12. Formed on the circumference of the intermediate section of the drive shaft 15 is a helical spline 19 which is coupled through spline linkage to a spline-shaped section 21 of a clutch inner 18b. A pinion 25 which is engaged or disengaged with a ring gear (not shown in the drawings) of an engine to be started is formed at the front end of the drive shaft 15. The pinion 25 is incorporated into the drive shaft 15. On the drive shaft 15, an overrun clutch mechanism 18 is movably fitted. The rear end of a clutch outer 18a of the clutch mechanism 18 is fitted to the front end of the carrier 16e. When an abnormal impact is applied to the clutch mechanism 18, the clutch outer 18a and the carrier 16e slip respective to each other to relieve the impact. At the front end (about one third of the total length) of the clutch inner 18b, a spline which meshes with the helical spline 19 is formed on the inner surface to form the spline-shaped section 21. Rotation of the armature rotary shaft 12 is transmitted via the planetary gear mechanism 16 to the clutch outer 18a of the clutch mechanism 18, then transmitted from rollers 18c via the clutch inner 18b and the helical spline 19 to the drive shaft 15. The rear end (about two thirds of the total length) of the clutch inner 18b is formed into an enlarged section 26, the inner diameter thereof is larger than the outer diameter of the helical spline 19. A space 20 is formed between the enlarged section 26 and the helical spline 19. A ring-shaped stopper 22 is disposed at the rear of the space 20. The stopper 22 is fixed on the drive shaft 15 by means of a ring 23. A spring 27 is laid down between the stopper 22 and the clutch inner 18b. When the drive shaft 15 is thrusted by the plunger rod 13a to move forward, the stopper 22 moves forward together therewith in the space 20. When the drive shaft 15 has moved to such a position that the pinion 25 is engaged with the ring gear of the engine, the front end 22a of the stopper 22 comes in contact with the shoulder (rear end face of the spline-shaped section 21) 24 between the spline-shaped section 21 and the enlarged section 26. Therefore, forward movement of the drive shaft 15 stops when the pinion 25 is engaged with the ring gear of the engine. When the electromagnetic switch is opened, the plunger rod 13a is returned rearward so that the drive shaft 15 with the stopper 22 is returned to the former position by the elastic force of the spring 27. According to the present invention, as described above, the pinion 25 and the drive shaft 15 are formed into an integral body. Consequently, number of the teeth of the pinion 25 can be reduced without consideration to the bottom thickness (root thickness) of teeth 25a of the pinion 25 or to the strength of the drive shaft 15, to increase the gear ratio of the pinion 25 to the ring gear. In an engine starter of the prior art, because a separate pinion is fitted on the circumference of the front end of a drive shaft, number of teeth of the pinion must be at least 8 in a module of 2.54 level, depending on the root thickness of the pinion or on the strength of the drive shaft. In the engine starter of the present invention, on the other hand, because the number of teeth of the pinion 25 can be freely set, an engine starter equipped with a pinion of 7 or less teeth can be made. Moreover, as the gear ratio of the pinon to the ring gear increases, the electric motor can be made compact and the total length of the engine starter can be reduced. When the number of teeth of the pinion 25 is reduced, inertia moment of the engine starter 10 viewed from the engine side increases. However, because the stopper 22 is disposed inside the clutch inner 18b, the diameter of the clutch mechanism 18 increases thereby the clutch capacity increases in view of the contact stress among the clutch outer 18a, the rollers 18c and the clutch inner 18b to improve the durability, and therefore no problem arises. Fig. 2 shows an engine starter 10 of another embodiment of the present invention. In Fig. 2, those which are assigned the same numbers as those in Fig. 1 are parts identical with or equivalent to those in Fig. 1. In this embodiment, a projecting section 31 which protrudes in the axial direction is formed at the rear end of a clutch inner 18b of an overrun clutch mechanism 30. This projecting section 31 is fitted with a minute clearance to the front end of a carrier 16e which is linked to the clutch outer 16a by fitting. When the gear ratio of the pinion to the ring gear is increased by reducing the number of teeth of the pinion 25, the pinion 25 makes larger number of revolutions in case the clutch mechanism 30 overruns, resulting in increased centrifugal force. In this situation, unbalanced weight in the direction of circumference in the clutch inner 18b causes eccentric rotations. In this embodiment, however, because the projecting section 31 of the clutch inner 18b is fitted to the inside of the front end of the carrier 16e with a minute clearance, such an eccentric rotation can be prevented. The projecting section 31 may also be fitted to the rear end of the clutch outer 18a with a minute clearance, or may be received by a bearing. Otherwise a part of the carrier 16e may be extended and fitted to the inside of the clutch inner 18b with a minute clearance. While an engine starter of such a constitution that the electromagnetic switch 13 is disposed at the rear is described in the previous embodiment, the present invention is by no means restricted to such a constitution, but can be applied to such a type as the drive shaft is thrusted by a shift lever to spring out forward.

Claims: An engine starter (10), comprising: an electric motor (11); a drive shaft (15) which is rotated by said electric motor (11) and is movable in its own axial direction, an end of said drive shaft (15) being formed into a pinion (25), said pinion (25) being engageable with a ring gear of an engine, said engagement being dependent on the axial position of said pinion (25); a stopper (22) fixed to said drive shaft (15); an overrun clutch mechanism (18) equipped with a clutch inner (18b), a first end of said clutch inner (18b) being engaged with said drive shaft (15), said clutch inner (18b) having a shoulder section (24) within the range of movement of said stopper (22), characterized in that at all positions of the stopper (22), the stopper (22) is within the clutch inner (18b). An engine starter as claimed in claim 1, wherein said stopper (22) comes into contact with said shoulder section (24) when said pinion (25) is engaged with said ring gear of the engine. An engine starter as claimed in claim 1 or 2, wherein said first end of the clutch inner (18b) is engaged with the drive shaft (15) by spline engagement. An engine starter as claimed in any preceding claim, wherein said electric motor (11) has an armature rotary shaft (12). An engine starter as claimed in claim 4, further comprising a gear mechanism (16) which is connected to said armature rotary shaft (12) and reduces the revolution speed of said armature rotary shaft (12). An engine starter as claimed in claim 5, wherein the rotation of said armature rotary shaft (12) is transmitted, via said gear mechanism (16) and said overrun clutch mechanism (18), to said drive shaft (15). An engine starter as claimed in any preceding claim further comprising; a plunger (13a) which thrusts said drive shaft (15) so as to move said drive shaft (15) in the axial direction thereof. An engine starter as claimed in claim 7, further comprising an electromagnetic switch (13) which controls the movement of said plunger (13a) and switches on the power to said electric motor (11).

Inventors: ISOZUMI, SHUZOU, ISOZUMI, SHUZOU, C/O HIMEJI SEISAKUSHO
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: F02N15
IPC codes: F02N15