Recoil-type starter for internal combustion engine

A recoil-type starter for an internal combustion engine. The starter includes a drum with a starting wire wound around it. The drum is disposed to confront a driven member such as a fly-wheel which is in turn operably connected to the engine. A starting pawl is pivotally secured to a peripheral portion of the drum, and is adapted to be pivotally moved to project radially outwardly of the drum into engagement with a cooperative projection formed on the driven member as the drum is rotated by pulling the starting wire, thereby to impart a starting inertia to the engine through the driven member. A stop is unitarily formed on the drum for limiting the outward pivotal movement of the starting pawl. The stop is positioned to abut a portion of the starting pawl close to the outer end of the latter at which the cooperating projection of the driven member contacts from the radially outer side of the drum. The radial component of the reactional force exerted by the projection on the starting pawl is received and supported by the stop, so that the starting pawl is free of bending force. It can withstand extended use without fatigue breakage.

The present invention relates to a recoil starter for starting an engine by 
pulling a starting wire wound around a drum mechanically associated with 
the engine. 
Recoil starters have been well known and practically used for starting 
small-output internal combustion engines. These known recoil starters 
incorporate a drum around which is wound a starting wire, as will be 
detailed later. The drum pivotally carries a starting pawl adapted for 
engaging a projection formed on the periphery of a fly-wheel of the 
engine, so as to cause a rotation of the fly-wheel when the drum is 
rotated as the wire is pulled. Consequently, the starting pawl is 
subjected to a large bending force or moment around its pivot axis, in 
addition to the compression force which acts along its longitudinal axis. 
This large bending force is apt to break or damage the pawl, as a result 
of the fatique of the material constituting the pawl caused by the 
repeated use of the starter, and shortens the life of the starter. 
It is therefore an object of the invention to provide an improved starter 
for an engine in which the bending force applied to the starting pawl is 
sufficiently reduced to prevent the pawl from being broken by the fatique 
of the material, thereby to improve the durability of the starter. 
To this end, according to the invention, there is provided a recoil starter 
of the kind described, characterized by comprising a stop provided on the 
drum for limiting the pivotal movement of the starting pawl, when the 
latter engages at its outer end a cooperating projection on a driven 
member, the stop being adapted to abut the starting pawl at a portion of 
the latter close to the outer end thereof from the radially outer side of 
the drum.

Before turning to the description of the embodiments, the drawback of the 
conventional recoil starter will be fully explained with reference to FIG. 
1, for clarifying the technical subject to be achieved by the present 
invention. 
FIG. 1 shows a typical conventional recoil starter. The starter has a drum 
A around which a starting wire is wound. Drum A is provided with a 
starting pawl B pivotally secured thereto. Pawl B is adapted to be pivoted 
outwardly, at the time of starting, i.e. when the wire is pulled to rotate 
the drum A, into engagement with a projection D formed on the periphery of 
a fly-wheel of the engine, so as to impart a starting inertia to the 
latter. The outward pivotal movement of the starting pawl B is limited by 
a stop E which engages the base portion of the pawl B. 
In the recoil starter having above described construction, due to a radial 
misalignment of the pivot axis G of the pawl and the end of the pawl at 
which it contacts the projection D, the tangential reactional force F is 
decomposed into a compression force F1 which acts in the longitudinal 
direction of the pawl B toward the pivotal axis G and a component F2 
acting in the direction at right angle to the compression force. This 
component F2 is considerably large and causes a bending moment in the pawl 
B around the pivot axis G. 
Consequently, the pawl B is apt to be broken along a longitudinal or 
breadthwise line which passes the pivot axis G, due to fatigue of the 
material caused by the repeated use of the starter. 
This problem of poor durability of the starter is, however, fairly overcome 
by the present invention, in which the stress caused by the bending 
component F2 is conveniently reduced to prevent the pawl from being 
broken, as will be seen from the following description of the preferred 
embodiment. 
Referring to FIGS. 2 to 5 inclusive which show the preferred embodiment of 
the invention, a casing 1 of a starter embodying the invention has at its 
mid portion a stationary or fixed shaft 2 around which a drum 3 is 
rotatably fitted. Drum 3 has a peripheral groove 4 receiving turns of a 
starting wire 5, one end of which leads to the outside of the casing and 
is connected to a starter handle 6. Drum 3 is normally biased in the 
clockwise direction as viewed in FIG. 2, by means of a coiled spring 7, so 
as to retract the starting wire 5 around the drum 3. It will be seen that 
the drum 3 is rotated counter-clockwise as viewed in FIG. 2, as the wire 
is unwound by pulling the starter handle 6, at the time of starting. 
Casing 1 is secured to the engine (not shown), while drum 3 is disposed in 
the vicinity of a driven member connected to the crank shaft of the 
engine, e.g. a fly-wheel 8, coaxially and in side-by-side relation with 
the latter. A boss 9 is formed on the peripheral portion of the drum 3, at 
one side of the latter confronting the fly-wheel 8. A pivot shaft 10 is 
provided on the boss 9. A starting pawl 11 has a bore 12 which receives 
the pivot shaft 10. In other words, the starting pawl 11 is pivotably 
supported by the pivot shaft 10. 
The fixed shaft 2 has at one end a peripheral frictional groove 13 which 
slidably receives a substantially U-shaped friction wire 14 having both 
ends connected to respective ends of starting pawl 11 through links 15, 
15. Loops 16 are formed on both ends of the friction wire 14 and at 
intermediate portions of the links 15, 15, so as to exert resilient force 
to bias the friction wire deep into the friction groove 13, thereby to 
ensure a predetermined friction between the wire 14 and the surface of the 
groove 13. 
Starting pawl 11 is made of a plastic having a large impact strength, e.g. 
polyacetal and is stepped as at 17 to have a thickened portion projecting 
toward drum 3. 
Step 17 is formed to an arcuate shape, for fitting around the periphery of 
boss 9 formed on the drum 3. Preferably, step 17 is brought into close 
fitting to the periphery of boss 9, when the aforementioned bore 12 is put 
into close contact with pivot shaft 10 by a load applied to starting pawl 
11. 
However, as a matter of fact, it is quite difficult to obtain such a 
dimensional relationship mainly for the reason of precision of the 
processing. Therefore, practically, the arrangement is such that the gap 
between step 17 and the periphery of boss 9 is made smaller than that 
between bore 12 and pivot shaft 10, in order to ensure a close contact of 
the periphery of the boss 9 with the step 17 which has a sufficiently 
large pressure-receiving area. 
At the side of drum 3 confronting fly-wheel 8 and in the vicinity of boss 
9, a step is formed constituting a stop 18 for the starting pawl. Stop 18 
is so designed and positioned that it may abut a portion of the starting 
claw near the outer end of the latter from the radially outer side of the 
drum, when the starting pawl is pivoted to project radially outwardly, 
thereby to limit the pivotal movement of the starting pawl. 
Fly-wheel 8 has a projection 19 adapted to be engaged by starting pawl 11 
when the latter is pivoted radially outwardly, at the time of the 
starting. 
In operation, as the wire 5 is unwound by pulling the starting handle 6, 
the drum 3 is rotated counter-clockwise as viewed in FIG. 2, along with 
friction wire 14 connected to starting pawl 11. However, due to the 
frictional engagement between friction groove 13 and friction wire 14, the 
latter is displaced slightly in the circumferential direction relatively 
to drum 3, so as to cause a radially outward pivotal movement of the 
starting pawl through links 15,15. Consequently starting pawl 11 is 
brought into contact with projection 19 of fly-wheel 8, so as to transmit 
the torque to the latter, thereby to start the engine. 
At this moment, as will be seen from FIG. 5, a circumferential or 
tangential force F is exerted by projection 19 on the end of starting pawl 
11. This force F is decomposed into a compressive component F1 which acts 
along the longitudinal axis and a radial component F2 which acts to cause 
the rotation of starting pawl 11. However, the radial component F2 of the 
force F is conveniently carried by the stop 18 which projects from the 
radially outer side of drum 3 in the vicinity of the outer projecting end 
of starting pawl 11, so that only the compression force F1 and a small 
radial compression force at the extreme end are applied to starting pawl 
11. 
Consequently, no substantial bending stress is caused in starting pawl 11 
by the bending force F2, so that pawl 11 is freed from the problem of 
breakage attributable to the fatigue of the material, and is rendered 
highly durable. 
In addition, the concentration of stress around bore 12 is conveniently 
avoided, because the area of step 17 is large enough to receive the 
compression force F1, so as to further improve the durability of the 
starter as a whole. 
Since starting pawl 11 is made of a plastic, it exhibits a large impact 
strength and produces no noise when it hits projection 19. At the same 
time, the plastic starting pawl never causes a substantial problem, even 
when it is broken and jammed between operating members. 
After the engine has been started, drum 3 is rotated clockwise as viewed in 
FIG. 2, due to the biasing force of spring 7, so as to retract starting 
wire 5, as handle 6 is released. During this clockwise rotation of drum 3, 
the friction appearing between friction wire 14 and friction groove 13 
conveniently causes a reverse pivotal movement of starting pawl 11, so as 
to retract the latter to the inside of the drum 3. 
Having described the invention through a specific embodiment, it is to be 
submitted here that the described embodiment is not exclusive and various 
changes and modifications may be imparted thereto. 
For instance, the step of the starting pawl can be dispensed with. 
At the same time, the starting pawl need not always engage the cooperating 
projection formed on the fly-wheel but may cooperate with any other 
suitable member provided on a driven member connected to the crank shaft 
of the engine. 
The pivotal movement of the starting pawl may be caused by any other 
suitable mechanism than described. 
Further, the starting pawl may be made of any suitable material other than 
plastic. 
Still further changes and modifications are possible without departing from 
the spirit and scope of the invention which is delimited solely by the 
appended claims.