Starter for an engine

An engine starter includes an electric driving motor having a drive shaft; a transmission pinion coupled to the drive shaft; a starter pinion meshing with the transmission pinion; and a swiveling device mounted on the drive shaft for pivotal motion thereabout. The starter pinion is rotatably supported in the swiveling device. A friction clutch torque-transmittingly couples the drive shaft to the swiveling device for causing the swiveling device to pivot about the shaft for placing the starter pinion in a working position when the shaft is rotated in a driving direction. The engine starter further has an overrunning device for transmitting a driving torque between the drive shaft and the transmission pinion solely when the drive shaft rotates at least at the same speed as the transmission pinion.

BACKGROUND OF THE INVENTION 
The currently used starters for engines, in particular piston-type internal 
combustion engines, include an electric driving motor having an axially 
displaceable starter pinion, which can be made to engage in the starting 
gear toothing through axial displacement with the aid of an actuating 
means, for example an electric lifting magnet. Such a starter is, for 
example, described in DE-A-42 04 124. 
Starters of an older design have a transmission pinion that is fixed 
immovably to the drive shaft of the electric driving motor and meshes 
continuously with the starter pinion, wherein the starter pinion can be 
made to engage in the toothing for the engine starting gear by swiveling 
it around the axis of the drive shaft. Such starters are known, for 
example, from DE-PS 325 109; 390 160; 369 639 and 490 441. 
These designs are relatively complex because they always require an 
additional actuation means that must be activated to make the starter 
pinion mesh with the toothing for the starting gear. 
SUMMARY OF THE INVENTION 
It is the object of the invention to create a starter with a simplified 
structural design and, accordingly, fewer structural components. 
The invention solves this with a starter of the above-described type, 
having an electric driving motor, the drive shaft of which is operatively 
connected with a transmission pinion via an overrunning clutch that locks 
in the rotational drive direction. The transmission pinion itself meshes 
with a starter pinion, mounted in such a way that it rotates on a 
swiveling device, which is installed such that it swivels around the drive 
shaft axis and is operatively connected with the drive shaft via a 
friction clutch. Such a starter has the advantage that when the electric 
driving motor is activated, it swivels the swiveling device with the aid 
of the friction clutch, thereby causing the starter pinion to mesh with 
the toothing for the starting gear and to maintain this contact as long as 
the driving motor is operational. As soon as the engine is started, with 
the engine speed as a rule being higher even when idling than the speed of 
the electric driving motor for the starter by taking into account the gear 
ratio between starter gear and starter pinion. As a result, thereby the 
electric driving motor for the starter would be forced to also rotate with 
increased speed. The series-connected overrunning device, however, has the 
effect of allowing a free running of the starter pinion and transmission 
pinion, depending on the speed of the starting gear, without the 
transmission pinion exerting a forced torque on the rotor of the electric 
driving motor. As long as the electric driving motor for the starter is 
switched on, the starter pinion continues to mesh with the starting gear 
via the friction clutch that acts upon the swiveling device. As soon as 
the power supply for the electric driving motor is turned off, the 
swiveling device can be turned with the aid of corresponding restoring 
means, for example a spring or even the force of gravity, thus disengaging 
the starter pinion. Additional actuators for actuating the swiveling 
device are therefore not needed. 
In order to further simplify the design and reduce the structural 
components, it is possible to dispense with the restoring means if in a 
further improvement of the invention, the electric driving motor is 
designed such that it can reverse its rotational direction. This 
arrangement has the advantage that by way of a respective electric 
switchgear, the electric driving motor briefly reverses the rotational 
direction at the exact moment when the starter switch is turned to the 
zero position and the electric driving motor is without power, so that the 
swiveling device is turned back to the rest position with the aid of the 
friction clutch that acts upon the swiveling device. The swiveling device 
can then be kept in this rest position by the force of gravity, if 
necessary with the additional effect of a lightweight retaining spring or 
a spring catch. Expediently the swiveling device effectively as a 
swiveling arm, so that the weight of the rotatably mounted starter pinion 
at the free end of the swiveling arm is sufficient as the retaining force. 
Another embodiment of the invention provides that the transmission pinion 
and the overrunning device are arranged jointly on the drive shaft. 
Yet another advantageous embodiment of the invention provides that the 
swiveling device is arranged on the drive shaft such that it can be 
swiveled. This results in a further reduction of the structural components 
as well as the assembly work. 
A further advantageous embodiment of the invention provides that the 
friction clutch is formed by at least one spring-loaded clutch component, 
which is frictionally engaged at least with the swiveling arm. The 
arrangement here can be such that the clutch component, for example, is 
connected with the drive shaft to rotate therewith as a unit and is 
frictionally coupled to the swiveling arm. The reverse design is also 
possible. For the simplest embodiment, for example when using one or more 
disk spring elements that can be prestressed, it is also possible to have 
a corresponding friction-lock effect between the drive shaft as well as 
between the swiveling device. Design and assembly are further simplified 
by such an embodiment. 
In yet another advantageous embodiment of the invention, it is provided 
that the swiveling device has stops for limiting the swivel movement 
between a rest position and an operating position. In addition to locking 
the swiveling device in the rest position, mounting a stop for limiting 
the swiveling movement in the operating position has the advantage of 
resulting in exactly definable pressure forces between the starter pinion 
teeth and the starter gear toothing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows the starting gear 1 for a piston-type internal combustion 
engine, which serves simultaneously as a flywheel and is equipped with 
toothing on the outside. An electric driving motor 2 is mounted parallel 
to the axis of starting gear 1. The drive shaft of the driving motor is 
connected to a transmission pinion 3, which meshes with a starter pinion 
4. The starter pinion 4 is arranged such that it rotates freely at the 
free end of a swiveling device 5 that is designed as swiveling arm, 
wherein the swiveling device 5 itself is arranged such that it swivels on 
drive shaft 8 of driving motor 2. The swiveling movement of swiveling 
device 5 is limited in both directions by stops 9 and 10 on driving motor 
2. 
As can be seen in FIG. 2, the arm-shaped swiveling device 5 has a 
"clamshell-type" design and is arranged directly on drive shaft 8 of 
driving motor 2. At least one spring-loaded clutch component, functioning 
as a friction clutch 6, is installed between drive shaft 8 and swiveling 
device 5. For the exemplary embodiment shown here, the friction clutch 
consists of a disk-shaped spring, which is supported at its inside edge on 
a collar of drive shaft 8 and at its outside edge on a counter-surface of 
swiveling device 5. The transferable friction force is defined by a 
suitable prestressing of the disk-shaped spring. As soon as drive shaft 8 
turns upon the start-up of driving motor 2, swiveling device 5 is moved in 
a rotational direction by way of the friction forces of friction clutch 6 
until it strikes one of the stops 9 or 10. As long as the driving motor 2 
is activated, the swiveling device 5 is held against the respective stop 9 
or 10, depending on the rotational direction. 
Furthermore, transmission pinion 3 is arranged rotatably on and relative to 
the drive shaft 8, and an overrunning (free wheeling) device 7 is 
provided, which is designed such that it transmits a torque for the 
starter operation in the rotational drive direction, that is, upon 
activation of the starter, and that it runs freely if the drive shaft 
rotates in the opposite direction. This free run also occurs if the drive 
shaft 8 rotates slower than the transmission pinion 3 or if drive shaft 8 
is at a standstill. 
While FIG. 1 displays the arrangement in the rest position, FIG. 3 shows 
the arrangement in operational position, with swiveling device 5 partially 
broken off. The diagrammatic display of overrunning device 7 shows that 
for the rotational directions of drive shaft 8 and starting gear 1, which 
are given through arrows 11, it is also possible to obtain a free run 
while the engine is operational and no torque is transmitted from 
transmission pinion 3 to drive shaft 8. 
In the exemplary embodiment shown here, if the starter is to be turned off, 
then the rotational direction of driving motor 2 is reversed quickly by a 
simple electrical switch, which is not shown here in detail, so that with 
the aid of friction clutch 6, swiveling device 5 is swiveled back from the 
operational position shown in FIG. 3, that is from stop 10 against stop 9 
and to the rest position. If the driving motor 2 is associated with 
starting gear 1 in the manner shown in FIG. 3, the gravitational force 
acting upon the swiveling device 5 is sufficient to keep this device in 
the rest position at stop 9, if such a starter arrangement is, for 
example, used with a stationary motor. The holding in place in the rest 
position can also be ensured with a suitably arranged lightweight 
retaining spring 12, as shown diagrammatically in FIG. 1, or by a 
corresponding snap catch. Return spring 12 here simply functions to 
maintain the swiveling device 5 in the rest position since the required 
torque for swiveling from the operational position (FIG. 3) to the rest 
position (FIG. 1) is effected in the exemplary embodiment shown by a 
reversal of the rotational direction of driving motor 2, so that the 
friction coupling is not stressed additionally to a large degree by this 
spring.