Engine starter with a corrosion resistant bearing

An engine starter suitable to be used under severe corrosive conditions is disclosed, wherein the inner race of the ball bearing for supporting the pinion driving shaft is made of a martensitic stainless steel hardened by a heat treatment, which is effective in maintaining a good sliding contact between the inner race of the bearing and the pinion driving shaft. The balls of the bearing may be covered by a seal at both open sides thereof; further, the front open end of the pinion may be closed by a cap.

BACKGROUND OF THE INVENTION 
This invention relates to starters for internal combustion engines, and 
more particularly to the overhang type starters in which the pinion is 
positioned in front of (i.e., to the outside of) the bearing for rotatably 
supporting the pinion driving shaft carrying the pinion. 
The overhang type starters for internal combustion engines are particularly 
liable to develop rust on the bearing rotatably supporting the pinion 
driving shaft. In order to make clear the reason therefore, let us first 
desribe the organization of such a starter, referring to FIG. 1 of the 
drawings. 
FIG. 1 shows the structure of the portion around the bearing of such a 
starter in an axial cross section. In FIG. 1, an output shaft 1 is coupled 
via a planetary reduction gear device 2 to the rotational shaft 3 of the 
armature of the starter electric motor (not shown); on the rear outer 
circumferential surface of the output shaft 1 are formed helical splines 
1a to which an overrunning clutch 4 is engaged at its inner surface, to be 
slidable in the axial direction. A pinion driving shaft 5, formed of a 
hardened quenched steel and disposed slidably on the output shaft 1, 
carries a pinion 6 formed integrally therewith at its front end. The 
overruning clutch 4 and the pinion driving shaft 5 with its pinion 6 
constitute the pinion assembly supported axially slidably on the output 
shaft 1. A ball bearing 7, made of a case hardened steel, comprises: an 
annular inner race 7a in slidable contact with the pinion driving shaft 5; 
an annular outer race secured to a front bracket 8 of the starter; and a 
plurality of balls 7c rolling therebetween; thus, the bearing 7 supports 
rotatably and axially slidably the pinion driving shaft 5. Further, a pair 
of metallic sleeves 9 are disposed between the output shaft 1 and the 
pinion driving shaft 5 so as to allow rotational and axial sliding 
movements of the pinion driving shaft 5 with respect to the output shaft 
1. A stopper 10 is secured to the front end portion of the output shaft 1 
via a ring 11 to limit the forward (toward right in the figure) movement 
of the pinion 6 by abutting on the stepped portion 5aof the pinion driving 
shaft 5 formed on its interior side surface. An electromagnetic switch 12 
shifts the pinion assembly via a lever 13, which is pivoted at its middle 
and is coupled at its upper end to the armature or plunger 14 of the 
electromagnetic switch 12 and at its lower end to the rear side of the 
overrunning clutch 4. 
The operation of the starter of FIG. 1 is as follows. When an electric 
current is supplied to the electromagnetic switch 12 from a storage 
battery, etc., the plunger 1 is attracted by the resulting magnetic force 
toward left in the figure; thus, the lever 13 rotates counterclockwise to 
drive and shift forward the overrunning clutch 4 and the pinion driving 
shaft 5, so that the pinion 6 is brought into engagement with the ring 
gear (not shown) of the engine. Further, due to the action of the 
electromagnetic switch 12, the starter motor is supplied with an 
energization current to develop a torque; the resulting rotation of the 
motor is transmitted via the planetary reduction gear device 2 to the 
output shaft 1, and further, to the pinion driving shaft 5 via the 
overrunning clutch 4; thus, the resulting rotation of the pinion 6 starts 
the engine. 
As point out first, the above type of starters suffer from the development 
of rust on the bearing. Namely, when water containg mud or salt is 
splashed upon the starter, as often happens in the case of the starter 
attached, for example, to an automotive engine or an outboard engine of a 
small boat, this corrosive water enters from the front opening to the 
interior portion at which the bearing 7 is located. This eventually 
results in the development of rust on the bearing 7. As a result, the 
smooth sliding contact between the inner race of the bearing 7 and the 
pinion driving shaft 5 is impaired. 
SUMMARY OF THE INVENTION 
Thus, it is a primary object of this invention to provide an engine starter 
in which the smooth sliding contact between the pinion driving shaft 
carrying the pinion and the inner race of the ball bearing rotatably 
supporting it is maintained for a long period of time even under a severe 
operation condition where water containing mud or salt is often splashed 
on the starter. 
The above object is accomplished according to this invention by an engine 
starter in which at least the inner race of the ball bearing rotatably 
supporting the pinion driving shaft is made of a martensite stainless 
steel hardened by a heat treatment. 
The martensite stainless steel hardened by a heat treatment is not only 
resistant to the development of corrosion, but also exhibits enough 
mechanical strength required for a material of the bearing. Thus, the ball 
bearing of the starter according to this invention is enhanced in 
durability and is resisitant to the development of rust, being capable of 
maintaining good sliding contact with the pinion driving shaft even after 
a repeated exposure to water containing mud or salt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Let us now describe preferred embodiments according to this invention by 
reference to attached drawings. 
The starter according to a first embodiment of this invention is 
structurally similar to that shown in FIG. 1 and described above; thus, 
let us refer again to FIG. 1. The difference between the above described 
starter and the starter according to the first embodiment of this 
invention lies in the material of the inner race 7a of the ball bearing 7; 
namely, the inner race 7a of the ball bearing 7 according to this 
invention is made of a martensitic stainless steel subjected to a 
hardening heat treatment. Otherwise, the starter according to the first 
embodiment is similar to that described above in its structure and 
operation. 
Martensite stainless steels, which typically contains carbon (C) in the 
range of from 0.15 to 0.65%, chromium (Cr) from 16 to 25%, nickel (Ni) 
from 1 to 3%, and silicon (Si) and manganese (Mn) under 1%, are not only 
resistant to the development of corrosion but are capable of being 
hardened by a heat treatment. The effect of utilizing a martensitic 
stainless steel as the material of the inner race 7a of the ball bearing 7 
on the operation of the starter is as follows. The inner race 7a of the 
ball bearing 7 in slidable contact with the pinion driving shaft 5 is made 
resistant to the development of rust. Thus, even when water containing mud 
or salt enters into the interior of the starter, the sliding inner surface 
of inner race 7a of the ball bearing 7 develops hardly any rust, and thus 
the smooth sliding contact between the pinion driving shaft 5 and the 
inner race 7a of the ball bearing 7 is maintained. In addition, since the 
martensitic stainless steel of which the inner race 7a is made is hardened 
by a heat treatment, the bearing 7 is capable of supporting a large load 
and enduring a high speed rotation. As a result, even after a long period 
of operation under severe conditions, the smooth siding contact and the 
durabililty of the bearing 7 is maintained; thus, the reliability of the 
starter is enhanced. 
FIG. 2 shows a starter according to a second embodiment of this invention. 
In the case of this starter, the ball bearing 7, whose inner race 7a is 
made of a martensite stainless steel hardenedd by heat treatment as in the 
above case, comprises a seal 7d covering the balls 7c at both front and 
rear open sides thereof; further, a cap 15 attached to the front end of 
the pinion 6 closes the opening at the front end thereof. Furthermore, the 
outer circumferential surface of the pinion driving shaft 5 in sliding 
contact with the inner race 7a of the ball bearing 7 is plated with 
chromium. Otherwise, the starter of FIG. 2 is similar to that according to 
the first embodiment. 
The starter of FIG. 2 has following additional advantages: Since the front 
opening of the pinion 6 is covered by the cap 15, the annular gap between 
the pinion driving shaft 5 and the output shaft 1 is protected from the 
intrusion of water and dust; further, since the ball bearing 7 is provided 
with a seal 7d, the rolling portion thereof is effectively protected from 
the intrusion of water or dust. Furthermore, since the sliding surface of 
the pinion driving shaft 5 is plated with chromium, the deterioration of 
the sliding contact between the inner race 7a of the ball bearing 7 and 
the pinion driving shaft 5 proceeds still more slowly. Thus, the starter 
according to the second embodiment is especially suited to be used under 
severe conditions where, as when attached to an outboard internal 
combustion engine of a small vessel, the starter is attached in a position 
and attitude in which the pinion 6 points upward and a large amount of see 
water is splashed frequently thereupon. 
The starter of FIG. 2 is capable of being modified: Although the front 
opening of the pinion 6 is covered by a cap 15 in the case of the starter 
of FIG. 2, the pinion 6 may comprises in its stead an integrally formed 
front end wall closing the interior thereof. Further, for the purpose of 
enhancing the water-and dust-proof structure as described above, drain 
holes for leading out the intruding water may be formed in the front 
bractet 8 at a position in front (i.e., to the right side in the figure) 
of the ball bearing 7. 
In the case of the above embodiments, only the inner race 7a of the ball 
bearing 7 is made of a matensite stainless steel; however, the outer race 
7b and the balls 7c of the ball bearing 7 may also be formed of a 
martensite stainless steel. Further, although the pinion 6 is formed 
integrally with the pinion driving shaft 5 in the above embodiments, the 
present invention is applicable to the case where a separately formed 
pinion 6 is secured to the front end of the pinion driving shaft 5. 
Furthermore, for the purpose of enhancing and maintaining the smooth 
sliding contact between the inner race 7a of the ball bearing 7 and the 
pinion driving shaft 5, grooves for holding and retaining lubricating 
grease may be formed on the inner circumferential surface of the inner 
race 7a. Still further, although the above embodiments comprises a 
planetary reduction gear mechanism, the present invention is applicable to 
the starters in which the reduction gear is of a different kind, or even 
is omitted.