Starting device for an internal combustion engine, especially a chain saw engine

Disclosed is a starting device for an internal combustion engine having a stationary bearing axle attached to the engine, a pulley rotatably mounted on the axle and adapted for accepting a starting rope wrapped thereabout, a recessed coupling attached to the drive shaft of the engine, coaxially surrounding the rope pulley in its recess and having a plurality of inwardly facing ratchet teeth. The starting device comprises an elongated pawl pivotably mounted on one side surface of the pulley, the pivot point being spaced radially from the rotational axis of the pulley; a follower pin protruding from the pawl in the direction away from the pulley side surface at a point spaced from the pivot point; and a spring member elastically engaging the distal end of the bearing axle and comprising an elongated guide slot for receiving the follower pin, whereby the spring member retains the pulley on the bearing axle and swivels the pawl radially outwardly into engagement with the ratchet teeth in response to rotation of the pulley.

BACKGROUND OF THE INVENTION 
The invention pertains to a starting device for an internal combustion 
engine, and more especially to a starting device for an engine adapted for 
driving a portable motorized chain saw. The device is of the type having a 
rope pulley which rotates as a wound-up rope is pulled off and is 
rotatably arranged on a stationary bearing axle, to which it is secured by 
a retention spring which engages the bearing axle with the ends of its 
legs, whereby the frictional connection which prevails between the 
retention spring and the bearing axle is used to radially outwardly swivel 
a pawl around an axis which is parallel to the bearing axis when the rope 
pulley is rotated in the starting direction. The pawl is supported on the 
rope pulley and engages it with the inner teeth of a recessed coupling, 
which is connected with the crankshaft of the internal combustion engine 
and which is coaxial to the bearing axle. 
In a known starting device of this type, two pawls are provided which are 
arranged diametrically to the bearing axle. With cams arranged 
eccentrically to their swivel axes, the pawls engage in a dog plate, which 
is configured as a double arm lever and which is connected with the 
retention spring in form-locking relation. In other known starting 
devices, the cams which are provided for swivelling the pawl are arranged 
approximately in the middle between the end of the pawl and the swivel 
axis of the pawl, and engage in slits, which, in one of the known 
embodiments, are provided in the longitudinal direction of the dog plate, 
or are configured obliquely to its longitudinal direction. Because of the 
large number of components used in the known starting devices, there is a 
relatively large amount of play of these components in the assembled 
condition because of the unavoidable production tolerances. The 
consequence is a considerable wear of these components, necessitating an 
extensive inventory of spare parts. 
SUMMARY OF THE INVENTION 
One object of this invention is to provide an improved starting device of 
the above-described type. 
Another object of the invention is to provide such a starting device which 
is considerably simpler in its construction, which requires fewer 
individual parts, and which has a lesser susceptability to breakdowns. 
In accomplishing the foregoing objects, there has been provided in 
accordance with the present invention a starting device for an internal 
combustion engine having a stationary bearing axle attached to the engine, 
a pulley rotatably mounted on the axle and adapted for accepting a 
starting rope wrapped thereabout, a recessed coupling attached to the 
drive shaft of the engine, coaxially surrounding the rope pulley in its 
recess and having a plurality of inwardly facing ratchet teeth. The 
starting device comprises an elongated pawl pivotably mounted on one side 
surface of the pulley, the pivot point being spaced radially from the 
rotational axis of the pulley; a follower pin protruding from the pawl in 
the direction away from the pulley side surface at a point spaced from the 
pivot point; and a spring member elastically engaging the distal end of 
the bearing axle and comprising an elongated guide slot for receiving the 
follower pin, whereby the spring member retains the pulley on the bearing 
axle and swivels the pawl radially outwardly into engagement with the 
ratchet teeth in response to rotation of the pulley. 
In one embodiment of the present starting device, the spring member, 
preferably of spring wire, comprises essentially parallel legs connected 
together at their ends distant from the bearing axle, each leg being 
subdivided into an end section which engages the bearing axle and a guide 
section forming the edges of the guide slot. The two sections are 
preferably at an obtuse angle with respect to each other. 
In another embodiment, the spring member is stamped from a substantially 
planar plate of resilient material, such as spring steel, and comprises a 
pair of legs terminating in opposing semi-circular shaped ring sections 
adapted for engaging with the bearing axle, and an inwardly directed slot 
formed in the yoke position connecting the legs. 
Preferably, in the engagement position of the pawl, the tip of the pawl, 
the pivot axis of the pawl and the axis of rotation of the pulley lie on 
two planes which intersect along the pivot axis of the pawl at an angle of 
at least about 90.degree..

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
It is provided in accordance with this invention that the two legs of the 
retention spring are at least approximately parallel to each other, and 
each of the legs is subdivided by a bend into an end section which lies 
against the bearing axle and into a guide section which forms an obtuse 
angle with the former, whereby a follower pin, which is arranged between 
the swivel axis, at a distance therefrom, and the top of the pawl and 
which projects from the pawl, engages in the two oblique guide sections 
which are connected with each other. The device in accordance with this 
invention can preferably be configured so that, in the engagement 
position, the top of the pawl, the swivel axis of the pawl and the axis of 
rotation of the rope pulley lie on two planes, which intersect along the 
swivel axis. The planes form an angle of at least about 90.degree., and 
therefore result in an optimum angle of engagement of 90.degree. during 
the transfer of force from the rope pulley to the recessed coupling. The 
retention spring in accordance with this invention assumes several 
functions, namely, the axial retention of the rope pulley, the override 
clutch, the retention of the pawl itself, and the function of the swivel 
means for the pawl. For each of these functions, a different component is 
required in the known starting devices. In addition, the spring can be 
prestressed against the pawl, in order to prevent a movement of the pawl 
as a result of vibration while in its rest position. 
Turning now to the drawings, the illustrated device serves for the manual 
starting of an internal combustion engine, which is not illustrated in the 
drawings and which is preferably provided as the drive for a protable 
motorized chain saw or the like, which is also not illustrated. The 
starting device comprises a rope pulley 1 having a groove cut into its 
circumferential surface, serving to accept a rope 2. At its outer end, the 
rope is connected with a handle, which is not illustrated, and, upon 
pulling of this handle, the rope unwinds from the rope pulley 1 in the 
direction of arrow 3, whereby the pulley rotates in a clockwise direction 
in the view according to FIG. 1. For this purpose, the rope pulley 1 is 
rotatably mounted on a bearing pin 5, which is attached to the ventilator 
housing 6 of the otherwise not illustrated motorized chain saw, in the 
manner which is illustrated in FIG. 4. The longitudinal axis of the 
bearing pin 5 thus forms, at the same time, the axis of rotation of the 
rope pulley 1. In the free end section of bearing pin 5, which extends 
beyond the rope pulley 1 when it is attached, a circular groove is 
machined. The base of the groove can be rounded in the longitudinal 
direction of the pin. 
On its reverse side, which faces the observer in the illustration in 
accordance with FIG. 1 and which faces away from the ventilator housing 6, 
the rope pulley 1 is provided with a projecting bearing hub 8 having a 
transition into a sickle-shaped bearing block 9, which is also cast onto 
the rope pulley and which contains a recess 10 which forms a part of a 
cylindrical sleeve. The bearing block 9 serves for receiving a pawl 11, 
which is illustrated in greater detail in FIGS. 5 and 6. This pawl can be 
made of a synthetic resinous material, for example, a polyamide such as is 
commericially available under the trademark Ultramid. The pawl manifests, 
for example, a thickened end section 13, which forms a cylindrical section 
on its outer surface 12. In the illustrated embodiment, the pawl 11 is 
inserted with this thickened end section into the recess of the bearing 
block so that it can be swivelled radially outwardly around the swivel 
axis which is indicated at B, when the rope pulley 1 is rotated in the 
starting direction, which is indicated with an arrow 14, as a result of 
longitudinal pulling exerted on the rope 2. The pawl 11 can also be 
configured as a rod, without the thickened end section. 
In its swivel motion, the pawl 11 engages via its pawl tip 15 with the 
inner teeth 16, indicated by broken lines, formed by shell 17 of a 
recessed coupling which is preferably integrally connected with a 
ventilator wheel 18 or the flywheel. This structure contains a machined 
recess 19 on the motor side, which serves for receiving a flange, which is 
not illustrated and which is connected with the crank shaft of the 
internal combustion engine, into which three fastening screws (also not 
illustrated) can be inserted. These pass through elongated holes 20 in the 
base 21 of the carrier recess. Of the numerous ventilator vanes 22 which 
are curved in the radial direction of the ventilator wheel 18, some are 
illustrated in FIG. 2 in an axial plan view. 
FIG. 1 shows the engagement position of the pawl 11, in which it engages 
via its pawl tip in a tooth base 24 of one of the teeth 25, which project 
radially toward the inside. The pawl thus carries along the recessed 
coupling 17 in the direction of the arrow 14. As soon as the internal 
combustion engine starts and the recessed coupling 17 overtakes the rope 
pulley 1 in the direction of the arrow 14, the pawl 11 is swivelled back 
radially toward the inside into its declutched position which is indicated 
by broken lines. 
In order to make it possible to swivel the pawl 11 radially outwardly into 
the engagement position, which is illustrated by solid lines in FIG. 1, a 
retention spring 26 formed from round spring steel wire is provided, which 
is illustrated in greater detail in FIG. 7. The retention spring has two 
mutually parallel legs, of which each is divided by a bend, indicated by 
27 and 28, respectively, into an end section 30 and 31, respectively, 
which lies against the bearing axle, and into a guide section 32 and 33, 
respectively, each of which forms an obtuse angle with its respective end 
section. In their seating areas 34 and 35, at which the end sections 30 
and 31 engage at least partly in the groove 7 of the bearing pin 5, the 
legs are curved away from each other. The end regions 36 and 37 which are 
located subsequent to the seating areas 34 and 35 are spread away from 
each other and thus facilitate the insertion of the retention spring on 
bearing pin 5, so that the two legs of the retention spring are seated 
against the base of the groove with an elastic prestress and thus can 
produce a frictional closure which holds the retention spring in its 
particular position on the bearing pin. 
A cylindrical follower pin 40 which is preferably integral with the pawl 11 
engages between the two mutually parallel guide sections 32 and 33 of the 
retention spring, which are connected to each other through the common 
yoke region 38. When the rope drum 1 rotates in the drive direction 14, 
the follower pin 40 moves against the guide section 32 of the retention 
spring 26 and is then moved in the direction of the yoke 38 of the 
retention spring as a result of the oblique orientation of this guide 
section, which forms an angle of about 45.degree. with the radial plane 
41, indicated by a dot-dash line in FIG. 7 and positioned in the axis of 
rotation A, and thus forms, with its associated end section 30, an obtuse 
angle of about 135.degree.. In this manner, a radially outwardly directed 
swivel motion of the pawl 11 in the counter-clockwise direction around the 
swivel axis B results, so that, with further rotary motion of the rope 
pulley, the tip 15 of the pawl 11 comes into engagement with the recessed 
coupling in front of the next available tooth 25 and can carry it along in 
the direction of drive motion. Thus, when the tip of the pawl 15 transmits 
the moment at point C of FIG. 1 in the form of compressive force, 
particularly advantageous transmission conditions result, because this 
point C, the swivel axis B of pawl 11, and the axis of rotation A of rope 
pulley 1 lie on two planes which intersect along swivel axis B at an angle 
of 90.degree.. This results in a minimum of required compressive force 
which is to be absorbed by the pawl 11 and its bearing block 9, thus 
assuring a considerable lever arm for this compressive force. As a 
consequence, a very small amount of wear and tear results as well as 
correspondingly long maintenance-free operating periods for the present 
starting device. 
The modified embodiment of a retention spring which is illustrated in FIG. 
8 is particularly suitable for industrial mass production. This retention 
spring 50 is produced by stamping from an essentially flat spring steel 
plate of about 1.2 mm thickness. The legs 51 and 52, which correspond in 
their effect to the end sections 30 and 31, also run parallel to one 
another and terminate with two semi-circular rings 53 and 54 which, with 
their cylindrically shaped inner edge 55 and under the pressure of the 
spring-elastically widened legs 51, 52 lie against the base of the 
circular groove 7 (FIG. 4) in the bearing axle 5, and there transmit the 
necessary frictional connecting force when the retention spring 50 is 
inserted into this circular groove 7 in its operating position. 
In order to make possible this spring-elastic stress which produces the 
necessary frictional pressure, the two legs 51 and 52 are connected with a 
common yoke 60 through two narrow webs 58,59, which are produced by 
rounded recesses 56,57. The yoke extends beyond the two rounded recesses 
56 and 57 toward the two semi-circular rings 53 and 54 and thus makes it 
possible that the legs 51 and 52 possess a considerable bending 
elasticity. For the formation of two guide legs 61 and 62, which 
correspond to the guide sections 32 and 33 of the retention spring in 
accordance with FIG. 7, a cut 63 is provided in the yoke 60 directed 
toward the center or the axis A of the rope pulley and the support axle 5. 
In the assembled condition, the pin 40 which projects from pawl 11 then 
engages in this cut and swivels the pawl, in the manner described above in 
connection with FIGS. 1 to 7, for the purpose of engagement with the teeth 
16 during the starting operation. 
For purpose of obtaining an axial prestress, the edge zone 64 and 65 in the 
cut 63 can be bent from the plane of the drawing toward the pawl, in an 
inclined manner, so that they prevent the pawl from moving out of 
retention under the influence of the vibrations which occur during 
operation of the tool. 
As a variation of the embodiment of cut 63, which is indicated by solid 
lines in FIG. 8, it is possible to configure the cut in accordance with 
the broken lines 66, so that it points a little past the center of the 
semi-conductor rings 53 and 54 and thus results in an inclined guide for 
pin 40 of pawl 11, anaglogous to FIG. 7.