Engine starter having planet reduction gear mechanism

A cylindrical yoke 3 of a d.c. motor of an engine starter having a planet reduction gear mechanism and a bracket 5 fitted on an extension of the yoke without relative rotation therebetween is formed integrally on an inner surface of the extension with internal gear teeth 4 of the planet reduction gear mechanism, which mesh with a solar gear 6 formed integrally on an armature shaft 2 of the motor through planet gears 7 supported by a flange 10 of an output shaft 11 of the starter. The motor is separated from the planet reduction gear mechanism by a flange 3b, 22 arranged therebetween and supporting a bearing 16 which supports the armature shaft.

BACKGROUND OF THE INVENTION 
The present invention relates to an engine starter and, particularly, to an 
improvement of such starter having a planet type reduction gear mechanism. 
FIG. 1 shows a typical example of a conventional engine starter having a 
planet type gear reduction mechanism. In FIG. 1, the engine starter 
comprises an electric d.c. motor having an armature 1 rotatably supported 
by a shaft 2 and a yoke 3 in the form of cylinder having a wall 31 and a 
front bracket 5 on an inner surface of which a component of a planet 
reduction gear mechanism is formed integrally. The component comprises an 
internal gear member in the form of a flange including an axial annular 
tooth portion extending toward the yoke 3 and having an inner surface 
formed integrally with gear teeth 4, and an annular projection 41 which is 
coaxial with the annular tooth portion in the opposite direction and 
defines a center hole. A solar gear 6 is formed on a front end portion of 
the armature shaft 2, with which planet gears 7 are meshed. The planet 
gears 7 are supported by bearings 8 which are, in turn, supported by 
support pins 9 implanted in a flange 10 of an output shaft 11. The output 
shaft 11 is supported by a sleeve bearing 12 which is supported by an 
inner periphery of the center hole of the annular projection 41 of the 
internal gear member. The front end portion of the armature shaft 2 is 
supported by a sleeve bearing 13 fixedly provided in an axial hole formed 
in an inner peripheral surface of a rear portion of the output shaft 11. A 
reference numeral 14 depicts a steel sphere arranged between ends of the 
armature shaft 2 and the output shaft 11 and functions to receive thrust 
load. A reference numeral 15 denotes a permanent magnet fastened on an 
inner peripheral surface of the yoke 3. The flange 31 functions to provide 
a thrust support for the planet gears and seals the planet reduction gear 
mechanism from the motor portion to thereby provide a dust-free structure. 
In operation, the armature 1 is energized by closing an engine key switch 
(not shown) and produces a rotational force under the influence of the 
magnetic field of the permanent magnet 15. The rotational force of the 
armature 1 is transmitted through the solar gear 6 on the shaft 2 to the 
planet gears 7 to rotate the latter to thereby rotate the output shaft 11 
at a reduced speed through the flange portion 10. The rotation of the 
output shaft 11 is transmitted to a ring gear of an internal combustion 
engine (not shown) through a pinion gear of an over running clutch (not 
shown) which is fitted on the output shaft 11 and housed in the front 
bracket 5. 
Since, in the conventional device, the internal gear member having 
internally projecting teeth which constitute a portion of the planet 
reduction gear mechanism is provided separately from the yoke and 
assembled thereto, the number of parts constituting the mechanism is 
relatively large, the structure thereof is relatively complicated and the 
assembly thereof is relatively difficult. 
Further, the partitioning effect of the flange portion of the yoke arranged 
between the motor and the planet reduction gear mechanism is not complete 
due to the existence of the center hole of the flange. It is thus 
difficult to assure a dust-proof structure for shielding one of them with 
respect to the other. 
A starter having a center bracket which is formed integrally with a yoke of 
a motor so that it covers the latter is disclosed in U.S. Pat. No. 
4,454,437. 
U.S. Pat. Nos. 4,488,073 and 4,520,285 disclose a starter in which an 
internal gear member is formed integrally with a center bracket. 
In any of these prior arts, it has been found that, although the number of 
parts is reduced, the rotational force of the armature shaft under shock 
load is transmitted to the yoke, causing the operational reliability of 
the starter to be degraded. Further, in order to provide a dust-proof 
structure, these prior arts propose the use of specially designed 
shielding member arranged between the motor and the planet reduction gear 
mechanism. 
SUMMARY OF THE INVENTION 
The present invention was made in view of the drawbacks of the conventional 
device, and its object is to provide an engine starter whose number of 
parts is relatively small and an assembling operation thereof is 
relatively easy, while improving operational reliability of the starter 
and providing a dust-proof structure without using any special shielding 
member. 
The engine starter according to the present invention is featured by an 
internal gear member constituting a planet reduction gear mechanism formed 
integrally with an end portion of a yoke and a flange portion having a 
bearing for supporting a shaft of a motor formed integrally on an inner 
surface of an intermediate portion of the yoke, i.e., between the motor 
portion and the internal gear member. With such structure of the engine 
starter as mentioned above, it is not necessary to provide the internal 
gear member and a center bracket therefore, separately, resulting in a 
reduction of the number of parts. 
The bearing supported by the flange portion acts also as a dust-proof 
partition between the motor and the planet reduction gear mechanism. 
The rotational force of the armature shaft under shock load is absorbed by 
a bracket of the starter, which is fixedly fitted peripherally to the yoke 
and supports the output shaft through a bearing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The FIG. 2 embodiment includes a d.c. motor having an armature 1, a rotary 
shaft 2 supporting the armature 1 and a yoke 3. The yoke 3 has a 
cylindrical body 3a including an end portion on an inner surface of which 
internal teeth 4 are formed integrally and an intermedial portion having a 
radially inwardly extending flange 3b formed integrally therewith. The 
rotary shaft 2 is supported by a bearing 16 supported by the flange 3b. On 
a front end portion of the rotary shaft 2 is a solar gear 6 formed 
integrally therewith, which meshes with planet gears 7 which in turn mesh 
with the internal teeth 4. An end portion of the yoke 3a is fitted to a 
front bracket 5 which surrounds an output shaft 11 and houses an over 
running clutch (not shown) mounted on the shaft 11. The fitting of the 
yoke 3 to the front bracket 5 will be described later. 
In this embodiment, the internal teeth 4 are integral with the yoke and the 
axial length of the starter is reduced since the flange 3b acts as a 
support of the internal gear. Further, due to the existence of the bearing 
16, an effective partition is formed between the motor and the planet 
reduction gear mechanism. Other components of this embodiment than those 
mentioned above are substantially the same as those of the conventional 
device shown in FIG. 1 and therefore details thereof are omitted for 
avoidance of duplication. The operation of this embodiment is also the 
same as that of the conventional device. 
FIGS. 3 and 4 show another embodiment of the present invention, wherein the 
yoke 3 has a generally cylindrical portion 3a formed integrally with a 
center bracket or flange 22 and with internal gear teeth 4 which mesh with 
planet gears 7. The center flange 22 is formed with a center hole 24 by 
which a bearing 16' is supported to support an armature shaft 2. 
The fitting between the yoke 3 and the bracket 5 is in the form of faucet 
joint. As shown in FIG. 4, the outer surface of the end portion of the 
yoke 3 includes four arched planes 22b connected by four flat planes 22a, 
and an inner surface of an end portion of the bracket 25 includes 
corresponding four arched planes connected by four flat planes 25b so 
that, by inserting the end portion 3a of the yoke into the end portion of 
the bracket 25 until it abuts an end face 25a of the latter, a faucet 
fitting is established therebetween with no relative rotation 
therebetween. 
Therefore, rotational force of the armature shaft 2 which usually acts on 
the yoke 3 to cause rotation thereof is transmitted through the faucet 
joint to the bracket 25 and absorbed thereby. 
A distance between the fitting planes and the armature shaft is preferrably 
selected as being larger than that between an outer surface of the 
cylinder portion 3a of the yoke 3 and the armature shaft 2. 
FIG. 5 shows another embodiment of the present invention, which is similar 
to that shown in FIG. 2 and in which the production of the yoke is 
facilitated. In FIG. 5, the only difference thereof from FIG. 2 are that 
an end portion 3c of a yoke 3 is stepped to make its diameter than that of 
the cylinder portion 3a, and that a center bracket or flange 3b is 
prepared separately and assembled to the stepped portion 3c of the yoke 3 
as shown as a substitution for the flange 3b in FIG. 2. With the increased 
diameter of the end portion 3c of the yoke 3, the assembling of the center 
flange 3b is facilitated. A diameter of a front bracket 5 is increased 
compared with that in FIG. 2 correspondingly to the increased diameter of 
the end portion 3c of the yoke 3.